US1727112A - Truing device - Google Patents

Description

sept. 3, 192.9.`

H. D. MAUNDAY TRUI NG DEVICE A Filed May 18, 1928 '7 Sheets-Sheet l l ATTORNEY Sept. 3, 1929. H. D. MUNDAY TRUING DEVICE '7 Sheets-Sheet 2 Filed May 18, 1928 INVENTOR. oracelJ/ldzy BY l ATTORNEY Sept. 3, 1929.

H. D. MUNDAY TRUING DEVICE Filed May 18, 1928 7 Sheets-Sheet 3 4^.; ATTORNEY- Sept. 3, 1929.\ H15. MUNDAY 1,727,112'

' TRUING DEVICE Filed May 18, 1928 7 Sheets-*Sheet 4 'UIMM IN V EN TOR.

LA ATTORNEY.

Sept. 3, 1929.

H. D. MUNDAY TRUING DEVICE Filed May 18, 1928 7 Sheets-Sheet 5 INVENTOR. Efface Mlm@ mi ATTORNEY,

Sept. 3,1929;- H. D. MUNDAY 1,727,112*

TRUING' DEVICE I Filed May 18, 1928 7 SheetS-Sheet 6 w in E l L; l

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Mg ATT'ORNEY Sept. 3, 1929. H, D, MUNDAY 1,727,112

TRUING DEVICE Filed May 18, 1928 7 Sheets-Sheet 1.7

m ATTO'RNEY,

Patented Sept. 3, 1929.

UNITED STATES HORACE D. MUNDAY, OF SCHENECTADY, NEW YORK.

TRUING DEVICE.

Application filed May 18, 1928.

This invention relates to a method and means of making true and keeping true the commutators and collector rings of electric machines, and in its preferred form has particular relation to a method and means of doing this while the machine is carrying its normal load, and of doing it automatically or with only nominal or casual attention.

From one cause or another the commutators and collector rings of many electric machines sooner or later get out of round. In the case of small machines the armature is usually taken out of the frame of the machines and the commutator turned in a lathe. The comf mutators of large machines are ground or turned with the armature in place. The apparatus now in general use for grinding such commutators comprises a base having thereon guides or ways, the base being set up on blocks on the floor or attached to some stationary part of the machine with the ways parallel to the commutator. On the base is mounted a carriage which, by means of a lead screw is moved parallel to the commutator. On the carriage is mounted a cross-feed slide which, by means of guides and screw is moved at right angles to the base of the apparatus, or in a radial direction to and from the commutator. On the cross-feed slide is mounted a small motor and grinding wheel, the small f f lathe tool.

In operation of this grinding apparatus now in use, the small motor driving the grinding wheel is started. The cross-feed slide is then advanced by means of its screw till the revolving grinding wheel rjust touches the rotating commutator. The lead screw in the base of the apparatus is then turned, drawing the grinding wheel along the length of the commutator. The cross-feed slide is then advanced a thousandth of an inch or so towards the commutator, and the grinding wheel again moved along the length of the commutator. The operation is repeated till all the flat spots an d ruts have been ground out of the commutator. Instead of the lead screw being turned by hand, often the lead 'screw is turned by another motor belted up to the pulley or handwheel of the lead screw, a switch thrown by hand being used to reverse this motor at each end of the commutator.

Serial No. 278,747.

In the operation of the grinding device just described it is evident that the operator must be present throughout the entire operation which may consume from several hours to a day. It is generally necessary partly to dismantle the machine to enable the operator to position the grinding apparatus in proper operative relation to the commutator and it is also generally necessary to take ofi all or some of the useful load from the machine.

In employing the apparatus constructed in accordance with the present invent-ion, I overcome the disadvantages just noted. In operation my improved apparatus is automatic and when initially adjusted and started it will continue the operation of grinding without further attention and will automatically stop after predetermined movement. In using the preferred form of my invention the apparatus may be applied to the commutator without dismantling or removing any of the parts of the machine and the machine may be kept in o eration under fullloadduringthe entire grin ing operation.

Numerous other advantages and objects of my invention will appear from the following description and explanation of the operation of my improved apparatus and method of grinding.

In a preferred embodiment, the invention comprises the abrasive mounted in some form of tool p ost or holder, means of advancing the abrasive toward the commutator or along the commutator, means for creating the force of some kind, which may be the spring, or weight or motor for causing the movement of the abrasive and means for hindering the motion for the abrasive, that is, a means which tends to retard or prevent motion of the abrasive toward or away from the commutator.

One effect of a hindering means employed by me is to prevent the abrasive advancing quickly into a low spot of the commutator as the low spot passes under the abrasive and to confine the rubbing of the abrasive to the high spots of the commutator. Or in case the abrasive does enter the low spot of the commutator the hindering means will offer a. high resistance to the backward or retrograde motion of the abrasive as the abrasive is being pushed back by the commutator surface onto the high spot. In either of these cases the abrasive will bear more lightly on the low spots of the commutator than on other portion of the commutator surface, with the ref sult that ultimately the commutator will be :light amount by the forcing backward of the abrasive by the 'high'ispot ofi the commutator. Y The weightV of the grinding apparatus may contribute materially to this effect and if desiredthe apparatus may beV :veighted to increase its inertia.l

The means of hinderingthe motion of-lthe abrasive forms an-important feature ofthe invention, together. with the fact that the force for movingthe abrasive is such that 5 ghe advancement of the abrasive, radially at least, is-harmlessly haltable on Contact with the commutator.

With al viscous substance interposed to hinder the advancement of the abrasive towards the commutator, permitting the abrasive to move forward only slowly towards the commutator, the abrasive will slowly advance till it strikes-the high parts of the revolving commutator. Since the speed of the commutator isfso greatin comparison with the slow speed of the abrasive that the abrasive is not ableI to f'eed forward into the low spots of the `commutator while the commutator is making one revolution, it is evident that the low spots of the commutator will not be touched till-all the'high spots have been worn down. v Consequently the commutator must necessarily become true.

In the use offriction hindering means for ftruingup a commutator there is the difference that in the case of friction-both the high partand the low part of the commutator are worn down at the same time-the high part being worn down heavily and the low part lightly. In the case of the viscous substancehindering means, as hasl been seen, the low part of the commutator is not touched at all`till7the high part has been worn down completely. How friction can be used 'to true upacommutator can be seen from the fact that the net force causing the advancement of the abrasive is only the excessoffthe spring or weight over the friction hindering means. On the other hand the total force necessary toecause a retrograde movement of the abrasive is equal to the sum of the friction and theforce of the spring or weight. Consequently the reaction pressure of the commutator on the abrasive will be much greater when the abrasive is being shoved backward from the commutator than when the abrasive is merely stopped in its advancement towards the commutator. After the high level part of the commutator comes under the abrasive and the abrasive necessarily ceases any further retrograde movement, the slight spring in the apparatus and its supports as a whole may be made to cause the abrasive to continue to exert the maximum pressure on the level high part of the commutator. Consequently, since the abrasive exerts a heavy pressure on the high part of the commutator and a light pressure on the low part of the commutator, the commutator will finally become true.

Some of the metals or alloys have the property of yielding or bending slowly when subjected to a certain pressure. Lead is such a metal; solder is another. This property can be used in a number of Ways to give a slow motion. For instance, a belt of lead or solder on pulleys will permit only a slow motion of the pulleys when the proper driving force is applied.

While in a preferred form of the invention the means used for hindering the motion of the abrasive are friction hindering means and viscous substance hindering means, sluggishly yielding metal and in certain cases relief springs, structural yield, inertia clock mechanism and an oil or other fluid pump.

In a. preferred form of this invention for certain purposes, the present grinding apparatus in the general form just described is taken and adapted to automatic operation.

To make for simplicity the small motor driving the grinding wheel is eliminated. To make it unnecessary to remove the brushholder arms, a long overhanging shaft or arm journalled in the cross-feed slide, carries at its extremity the abrasive or grinding member, and is preferably of a length to carry the abrasive completely across the commutator. The extremity of the arm is insulated from the main part of the arm which is surrounded by a libre sleeve to avoid increasing the chance of a ground, or a flash-over between adjacent brush-holder sets.

The motor driving the lead screw is preferably retained. But to avoid the necessity of reversing this motor at .short intervals at each end of the commutator, only one or a few traversing cuts are taken across the commutator, one cut at least however, being preferably of substantial depth. When the gruding device is in action the abrasive should preferably move from the inside end of the commutator to the outside end, and not the reverse. At the outer end of the commutator the abrasive should automatically stop and without the necessity of prompt attention by the operator. To increase the chance that the motor driving the lead screw of the device will stop when the abrasive reaches the outer end of the cominutator, a direct-current motor is used in what might be called a stallable manner. Some current-limiting means, such as a rheostat in the armature circuit, is used to prevent any dangerous amount of current in the armature, though the motor may be indefinitely stalled or stopped with the current still in the armature.

Several devices are used to make sure that the abrasive will not be carried beyond the end of the commutator, or beyond the shrink ring in the middle of the eommutator, if the inner half of a cominutator having a shrink ring is being trued. One device of this kind is a push button mounted so as to be operated by the saddle or carriage oi' the truing apparatus and throw out the circuit breaker. Another device is a. conical-ended nut clamped to the lead screw in the proper position to open up the split nut attached to the saddle and throw it out of engagement with the lead screw when the abrasive has reached the desired limit of its travel. A third device is a clamp attached to the ways of the base of the apparatus in position to block the travel of the saddle or carriage beyond the clamp.

To get a slow travel of the abrasive across the commutator some form of hindering means is used to hinder the motion of the .lead-screw. This hindering means should be of the delay type or at least include a hindering means of the delay type. rIhe lead-screw may be thrown out of action (by opening up the split nut attached to the carriage) and the saddle moved along the base by a direct pull; in this case friction hindering means could be used jointly with delay hindering means, but should preferably not be used alone.

Instead of using a hindering means of the delay type to hinder the motion of the leadscrew, a train of worm gears and Worms could be used between the small driving motor and the lead-screw, for the purpose of getting a very slow motion of the lead-screw as compared to the motor speed.

To get the radial advancement of the abrasive towards the coinmutator as the abrasive travels along` the length of the commutator from the inside end to the outside end of the commutator, the means for advancing the abrasive radially towards the commutator may be operatively connected to the means for advancing the abrasive ayially along the commutator, to the end that the radial advancement of the abrasive is proportional to the axial advancement of the abrasive; or, if not eXactly proportional, increasing as the axial advancement increases.

In certain cases the abrasive may be ad-' cipally, but also relief spring hindering means, the hindering means due to a sluggishly yielding or sluggishly distortable metal, such as lead or solder, as well as the hindering means due to the natural, structural yielding of the apparatus as a whole and its inertia. The weight to increase inertia may be embodied in the balance wheel of clock mechanism. Means are also provided to utilize a liquid to furnish hindering means of the delay type for use in certain cases. It will of course be understood that for certain purposes any of these hindering means may be used alone.

The advancement of the abrasive which may be an abrasive block or an abrasive wheel, radially towards the cominutator may be brought about either by the rotation of the abrasive-carrying arm journalled in the cross-feed slide, or by the radial movement of the cross feed slide itself, or bythe base of the apparatus being slightly out of parallelism with the commutator. In this latter case the axial movement of the carriage will necessarily cause a proportional radial movement of the carriage and ab asive towards the commutator.

The cross-feed slide may be operated by a screw mounted in bearing blocks attached to the carriage and in engagement with a twopart nut attached to the cross-feed slide. This screw and nut have a line thread and a coarse thread, the line thread being used when the cross-feed slide is to be advanced positively, and the coarse thread when the cross-feed slide is to be advanced non-positively.

Provision is made in the apparatus for advancing the abrasive radially without at the same time advancing it axially. In this way a local fiat spot in the commutator can be trued up, or a. neck7 cut in the inner end of the commutator or the outer end of the commutator cut down. If an abrasive wheel is used in this case means are provided so that the wheel can be rotated by the leadscrew, the split nut attached to the carriage being thrown out of engagement with the lead screw so that no axial movement will be given to the abrasive wheel. Specific forms of my apparatus wherein a rotary abrasive wheel is employed or other forms of abrasive, wherein theabrasive material is fed to the ceinmutator in a direction, tangential thereto,` forni the .subject mattei' of a copending application tiled by me.

Then asphalt is employed as a hindering means, for the radial motion of the abrasive, it may be applied hot to the apparatus by smearing it on the surface of some part which normally rubs against the surface of some other part; thus .it may be applied to the surface of the cross-feed slide that normally slides along the carriage. lVhen the asphalt is cool, the cross-feed slide can still phalt. Vhile the asphalt is preferably applied hot it may be applied in the form of an asphalt paint, the solvent then being allowed to evaporate.

The asphalt may be so viscous at room temperature that it may require hours or days for the part to move a fraction of aninch; or, on the other' hand, in certain cases, it may be so soft that the eye can see the motion of the part. The principle'of operation is that the radial advancement of the abrasive will be so slow in comparison with the speed of rotation of the commutator that the abrasive will not have time to follow up into the low part of the commutator in the short time that is required for succeeding high partv of the commutator to go under the abrasive.

lt will thus be Vseen that in the operation of my improved method of grinding, there is a certain relation between the rate of advancement of the abrasive and the speed of rotation "i of the commutator.

Aing hindered by the asphalt or other hindering means, so that, for example, the crossfeed slide may be manipulated by hand so as quickly-to bring the abrasive into contact y with or near to the commutator, preliminary to automatic action.

It has been shown how a simple application of delay hindering means of the viscous substance type to the apparatus for moving the abrasive, will enable such apparatus to operate automatically in truing a commutator. It has also been shown how the application of friction to such apparatus will enable this apparatus to operate automatically. In certain cases it is desirable to employ both the friction hindering means and the viscous substance hindering means at the same time. It is to be noted that in the use of the particular friction means above described, the low spot of the commutator is always ground, through lightly, as well as the high spot and in certain cases where it is desired to true up a commutator with a minimum of copper loss, the use of such hindering means alone might at times be objectionable. In using delay hindering means merely of the viscous substance type non-positively, there is nothing to withstand the reaction thrust of the high part of the commutator against the abrasive except the resistance due to the viscosity of the asphaltso that with soft asphalt or other soft viscous material there may be a slight `yielding of the cross-feed slide or other movable partwhen the high part of the commutator comes under the abrasive. If however we employ in the apparatus, both the viscous substance hindering means and friction' hinderingmeans, it isclear the apparatus will-not grind the flatl spots ofthe commutator and consequently not cause unnecessary wearing o'f the commutator and at the same time such apparatus, due to the viscosity of the asphalt and the friction will' strongly resist the reaction thrust ofthe high parts of the commutatoras they come under theabrasive so that'the high spots `will be quickly andfeffectivelygrounddown.

Numerous other advantages and objectsl of`v my invention will appearfro'mthe following description taken in connection with the accompanying drawing wherein:

Figure l, is a perspectivey view, partly in section und partly broken away, of oneV form of apparatus constructed in'a'ccordance with my invention and showing the same appliedto'thek commutator of an electric machine;

Figure 2, is a side elevation, partly'in'section, of the structure shown in Figure '1, totogether with-the means for firmly securing such structure in position in proper relation to thei commutator Figure 3, is a top plan view ofthe structure shown in Figure l;

Figure l, is a sectionalviewtaken on the line lf-4 of'Figure 3';

Figure 5, is a sectional View taken on the line 5-5 of Figure 3;

Figures 6 and 7 are top and end elevations respectively, of the two-part nut employed as part of the feeding means;

Figure 8, is va sectional viewtaken onthe line 8 8 ofFigure 3 and showingin-elevation the abrasive block` and its holden;-

Figure 9, is a diagrammatic view of'a circuit control for a feeding motor;

Figure 10, isv` a diagrammatic View o'f a circuit control foran electrical heating means used to regulate the viscosity ofasphaltemployed for hindering motion of the abrasive;

Figure 1l is aV detail view, of a modified abrasive member and 'its holder;

Figure l2 is aside elevationofa -modiiied form of commutator truing apparatus applied to a dynamo electric machine commutator; i

Figure 13 is a top plan view of another modified form of truing apparatus applied to a commutator.

Referring to the drawings, Figures l-ll show a preferred form of the invention. On a longitudinal base 51 having ways or guides in the sides 52 of a dovetail tongue 53, is slidably mounted a carriage 54C, with a complementary dovetail groove in its face litting over the dovetail tongue 53 of the base. A lead screw 55 with suitable bearings in lugs 56a and 561? laterally projecting from eitherv endof the base, and in'v engagement with the split nut 57 formed of parts 57@1 and 57" serves as the positive mean'sof moving the carriage along the base 51; that is, parallel or generally parallel to the commutator when the apparatus is set up for grinding commutatore.

The carriage fl has on its upper face a dovetail tongue 58 at right angles to the base. Slidably mounted on the carriage 54 is the cross-feed slide 59; a complementary dovetail groove in its lower face fitting over the dovetail tongue 58 of the carriage. The crossfeed slide is moved along the carriage by a feed screw 61 mounted in bearing blocks 62 and 63 attached to the carriage. There are two threads of different pitches on the feedscrew and in the open-sided, two-part nut 64 with which it cooperates to move the crossfeed slide. This two-part nut, shown in detail in Figures 6 and 7, is reversibly attached to the cross-feed slide, so that either thread may at will be brought into threaded engagement with the feed screw 61; the liner thread 65 when a positive or non-reversible motion of the cross-feed slide is desired and the coarser thread 66 when a non-positive or reversible motion is desired. In attaching this two-part nut to the side of the cross-feed slide there is secured by the screw 66a between the cross feed slide and the two-part nut, a spacing member 67 with a complementary but threadless semi-circular bore 68 facing and closing with a little clearance the open side of the open-sided two-part nut 64, the said nut being slidably secured to the cross-feed slide by the cap screws 69 through elongated holes 69a. Beyond the bearing block 62 extends for some distance a portion of the feed screw 61 threadless but of unreduced diameter, to the grooved hand-wheel 70, to which it is slidably secured by the key 70. Surrounding the outer part of the feed screw between the bearing block 62 and the handwheel 70 is a pair of concentric tubes 71 and 72. the inner tube 71 being secured by the cap screws 7 3 through its flange 74 to the bearing block 62. The outer tube 72 is optionally secured by the clamp 75 to the hub 76 of the hand-wheel 70. The hand-wheel rotated by means of the solder wire or ribbon 77 wrapped around the hand-wheel, 70 and a weight 78 attached to the free end of the wire 77. Between the inner and outer tubes is a coating of asphalt 79 or other` viscous substance to hinder the rotary motion of the outer tube on the inner tube. One reason for using the sluggishly yielding solder wire 77 as a hindering means in addition to the hindering means of the asphalt 79 is to provide additional hindering means if the asphalt should become too soft-as by overheating by the thermal controlling meansto function efliciently in a hindering way. 1f for instance the abrasive is being advanced towards the commutator by means of the cross-feed slide 59 actuated non-positively by the coarse thread 66 of the feed-screw 61,

and without cooperating frictional hindering means, it is possible that very soft asphalt might permit a slight to-and-fro movement of the carriage that might prevent to some extent the most efficient truing of the commutator. On the other hand the coating of asphalt might be shattered by a sudden blow, the asphalt hindering effect being thus destroyed. l/Vith a slight rotary to-and-fro movement of the outer tube 72 due to the alternate coming under the abrasive of the low part and of the high part of the commutator, the shattered particles of asphalt might lack the quietness that is conducive to their proper knitting or coalescing. The use of the solder wire 77 will give the shattered particles of asphalt a better chance to knit, so that the asphalt soon can begin to function efficiently as a hindering means. The shattering of the asphalt might be due in part to a temperature too low for that particular grade of asphalt. The solder or lead wire however is not likely to be injured much in a hindering way by the ordinary changes of temperature.

Provision is made for a slight relief movement of the cross-feed slide 59 independent of the movement of the two-part nut 64 by the compression of one or the other of the relief springs 80. The screws 81 secure, slightly swivelly, the inverted L-shaped plate 82 to the spacing block 67. Stiff spiral springs are mounted on cap-screws 83 passing freely through plain holes in the plates 82 into threaded anchorage in the spacing block r67. The spiral springs are compressed to any predetermined initial stress by adjustment of the nuts 84. For the purpose of avoiding all lost motion between the plates 82 and the two-part nut 6/1 there are four adjustment cap-screws 85, secured by the jam-nuts 86. By entirely compressing the springs 80 by screwing up the nuts 84 the relief action of the device is annulled, the plates 82 then being fixedly held against the spacing block 67.

Attached vto the bearing block 62 by the flexible support 98 is the electric lamp 99 in circuit with the current-controlling rheostat 100 and thermostat 1002*. The lamp 99 is used to heat the asphalt 79 between the concentric tubes 71 and 72, thus controlling the viscosity of the asphalt 79 between the tubes 71 and 72, and consequently controlling the motion ofv one tube relative to the other. Without the thermostat 100a being in use, the heat received by the asphalt will depend on the dista-nce of the lamp 99 from the tubes 71 and 72, and on the current in the lamp as modified by the rheostat 100, and by the degree of interposition of the movable reflector 101 which may be rotated around the lamp socket 102 to partially or completely screen the tubes 71 and 72 from the lamp 99. Not all of these means Ot control need be used at one time.

llO

,Further control of the movable tube 72 may be secured through varying the number of 4sections of. the actuating weight 78 in use.

cap and bottoming on the lower half ofthe y bearing are used to adjust the bearing, as-by prevent-ing any possi-ble spring in the bea-ring cap 1from gripping the arm 112 tooclosely. A strip of felt 133 in the slotted opening in the bearing prevents the entrance of abrasive powder and copper chips to thebea'ring. Surrounding the outer part of the'arm112, is a pair of telescopic tubes 116 and 117, which, with the coating of asphalt 118 betweeny them constitutes one lof the means of-hindering the rotation of the arm 112. -The inner tube 116 by means of the cap screws 119 through holes in the tube flange 121 is attached to the lower half of the bearing block 111. The `outer-tube 117 is optionally clamped bythe clamp 122 to the collar 123, which is adjustably :secured to the arm 112 bythe set screw 124 setup against a copper disc to prevent the marring of the arm 112. The hindering effect of the asphalt coating is modified by controlling its viscosity, which is in turn controlled by the heat received fromA the electric larnp 125, this heat depending on the position of the lamp by flexure of the adjustable support, or by the adjustable interposition of the shade rotatable around the lamp socket to act as a screen between the lamp 125 and the tubes 116 and 117, or by controlling the current in the lamp by means of a rheostat or thermostat.

On the opposite end of the bearing block 111 is a friction hindering means. On the arm 112 between the end of the bearing block 111 and the worm gear 141 is a grooved and loosely litting collar 142. This collar lits somewhat loosely ony the' key 143, which also serves together with the set screw 144, to secure the worm wheel 141 tothe arm :112. This set screw k144 with its inner end imbedded in a depression in thelkey-143 serves also to keepfthe-key 143 assembled with the worm-wheel l141 whenever the arm 112 is moved 'axially to another position inthe bearing block 111. lThere is no keywayin the arm 112. The length of the key beyond the face of the worm-gearand towards the bearing' block 111 is slightly longer than the thickness ofthe collar-142, thus serving as a convenient spacing member whenever the arm'112 moved axially inthe bearing; block, the end ofthe keybeing `broughtup against the end of thebearingblock 111. Thecolla-r 142 may conveniently .have` `a few thousandths of an vinch or more clearance both in the bore and .in its keyway.

Partly surrounding the collar 142 and positioned in the groove thereof is the clamp 146, the two members of which 147 and 148 are clamped together by the cap-bolt 149. The clamp member 147 has threaded in its upper end the stud 150 to which is swivelly secured, by the thumb-screw 151 the bracket 152, to which is adj ustably attached the bar, 153 bearing the weight 154 of one or more sections 154a and 154", and which are slidably adjustableon said beam, to which they are secured by the set-screws 155. The beam has a right- ;angled end member 155a on which it may rotate being then secured by the set-screw 1551. This end member 155@ may be used for securing the beam 153 to the bracket 152' when it is necessary to clear some obstruction, such as avbearing; in which case bolts 156 and 157 areused t0 secure the right-angle end member 155. 1n each of the two clamp members l147 and 148is a threaded hole 158 and 159 of a size to receive the threaded end of the stud 150. By this means the stud I150 can always be positioned in al vertical or generally vertical direction regardless of whether the apparatus is set up with one side or the other at the bottom, as may be desirable in some cases. lGauge 160 aids in determining the angular position of the arm 15.3.

The object of having the beam 153 swivelly adjustable on stud 150 is to divide the pressure effect of the weight 154 into two cemponents, one component tending to rotate the arm 112 and the other component tending to prevent the rotation ofthe arm by causing friction between the collar 142 (loosely keyed to the arm 112) and the adjacent end of 'the bearing block 111. rlfhis can be seen more clearly if the two eXtreme positions of the beam 153 be considered. 1f the beam is in a position at right angles to the arm 112, it is evident that there will be no tipping of the collar 142 and c-onsequentlyno friction between the collar 142 and the end of the bearing block 111. Hence, in this position, all the effect of the weight will be spent in rotating the arm 112 and none in vhindering the rotation of said arm. The other extreme position of the beam 153 is thatparallel to the arm 112.l In this extremeposition it is evident that therefwillbe no tendency of the weight 154 to produce rotation of the arm 112, the only eect of the weight being to tip the collar 142, cause friction between the collar 142 and the end of the bearing block 111, and thus hinder, or rather prevent, the rotation of the arm 112. Between these two extreme positions, on the one hand of all rotary effect and no hindering effect, and on the other hand of all hindering elfect and no rotary eliect. there must be some middle position where the rotary effect will just overcome the hindering effect. This position, or one somewhat nearer that of maximum rotary effort, will generally be the more desirable position in which to keep the beam 153. This position can be easily found, if not marked on the apparatus, by loosening the clamp 122 on the tube 117 to eliminate the viscous substance hindering effect, and then slowly swinging around the weighted beam 153, from an initial position parallel to the arm 112, till the arm begins to move. If the bearing cap is not set up tight enough to give a clamping effect, the position so found will be independent of the weight 154 or its position on the beam 153. Under these conditions the rotary effect of the weight 154 on the arm 112 and the friction hindering effect on the arm 112 will increase or decrease together, the latter being a certain percentage of the former. This percentage can be changed by moving the beam 153 to a new position.

From what has been said it is evident that by loosening the clamp 122 the arm 112 may be rotated against a friction hindering effect only; or by tightening up on the clamp 122 and keeping the beam 153 at right angles to the arm 112 the arm'112 may be rotated against a viscous substance hindering effect only; or with the beam in an intermediate position, both the friction hindering effect and a viscous substance hindering effect will be in operation together. It may be noted that by tightening up the cap screws 131 to grip the arm 112 a little another friction hindering effect is available; this friction effect does not vary with the angular position of the beam 153.

In the methods that have been described for advancing the abrasive member either by the advancement of the cross-feed slide 59 or by the rotation of the arm 112, the means of advancement of the abrasive member have been independent of the movement of the carriage. Means are provided however for advancing the abrasive proportional, or substantially proportional, to the movement (axial) of the carriage 54. Attached to the lug 56a laterally projecting from the base 51 of the apparatus, by the cap screws 171, is the strap 172, swivelly securing by the cap screw 173 one end of the round bar guide 174, the other end of which is vertically adjustable and securable by the thumb-screw 175 slidable in the slot 176 of the strap 177 swivelly secured by the cap screw 178 to the lug 56b projecting laterally from the base of the device. Gauges 178a and 178b aid in securing the proper slope of the round bar guide 174. Sliding on the round bar guide 174 is the slotted shoe 179 adjustable as to clearance b the screws 180. Integral with the shoe 179 is the vertical stud 181, which forms a pivotal support for the block 182 with a capped bore 183 that slidingly receives the rod 184 threaded into the member 148 of the clamp 146.

' abrasive.

The reason for having this round'bar guide 174, slightly adjustable vertically (thus throwing it slightly out of parallelism with the arm 112 and the base 51 of the apparatus) is to advance the abrasive member 115 enough, as it is carried along the length of the commntator 113, to make up for the wear on the This guide is intended for use with an abrasive block rather than with an abrasive wheel. The guide can be thrown out of action to a limited extent by loosening the thumb-screw 175; or it may be thrown completely out of action by unscrewing the outer half of the rod 184 from the coupling nut 184% or by releasing the rod 184 from the block 182 by taking out the screws 185 and removing the cap 186.

A still simpler way to advance the abrasive is to set up the apparatus with the base 51 slightly out of parallelism with the axis of the commutator 113, the body of the abrasive coming progressively nearer the commutator as it travels along the length of the commutator, the endeavor being to advance the body of the abrasive to the approximate extent that will result in a cylindrical commutator rather than in one slightly tapering.

Provision is made for another means of advancing the abrasive proportional to the movement of the carriage along the length of the commutator. This means consists in an operative geared connection between the worm gear 141 and the lead screw 55, the latter being the driving member, and forming, through the coarse thread 187, in reality a long spiral gear meshing with the spiral gear 188 secured by the set screw 189 and the key 190 to shaft 191 driving the gear unit 192 and 193 secured thereto by the set screw 194, one gear 192 of said gear unit optionally meshing with the gear 195 of the shftable gear unit 195-196, which is securable and slidably adjustable by a set screw and key on the shaft 199. Shaft 199 has suitable bearings in the sides 200 and 202 of the gear housing 200-201-202, (201 being the base supporting the sides) and is flexibly 'coupled by the coupling 203204 to the shaft 205 driving the worm 206 slidably secured thereto by the lieyway 207, said worm 206 meshing with the worm gear y141 attached to the arm 112 carrying the abrasive member. Preferably the thread and teeth of the worm 206 and worm gear 141 are of such a pitch that the worm gear 141 can not act as a driver to drive the worm 206. The shaft 205 has suitable bearings in the bearing lugs 208 and 209 projecting from the base or plate 210, the latter being secured to the side of the cross-feed slide by the screws 211. By removal of the bearing caps 213 by unscrewing the screws 214, and by taking out the coupling screws 215, the shaft 205 and worm 206 may be easily removed from the apparatus. The worm 206, by means of a short key in the worm, is

splined on the shaft 205. The purpose of re- -moving the worm 206 is to make it possible to drive the arm 112 independently of the worm 206, using instead of the worm a motor to drive the pulley 216. However, if the thread and teeth of the worm 206 and worm gear 141 are of such a pitch that the worm gear will drive the worm, then it will not be necessary to remove the'worm 206 when the arm is rotated by means of a motor and the pulley 216. In this latter case the spiral gear 188 should be shifted on the shaft 191 till it is out of engagement with the lead screw 55. Another means of rotating the arm 112 independently of the lead screw 55 is by using a motor to drive the shaft 191. The operative connection between the driving motor and the shaft v191 may preferably take the form of a telescopic shaft, with a universal coupling at either end of this telescopic shaft to make connection to the shaft 191 and to the motor shaft. When the shaft 191 is driven in this way, the spiral gear 188 will be shifted out of engagement with the lead screw 55. rlhe gear housing 200-202 is attached by the screws 216a through the base 201 to the lug 216b proj ecting from the end of the carriage 54.

As said before, the gear unit 195-196 is shiftable, and when shifted from the position as seen in Figure 4 to the right as far as possible, the gear 195 is taken out of mesh with gear 192, and gear 196 comes into mesh with the intermediate gear 217 which is always in mesh with the gear 193 of the gear unit 192-193- This sifting of the gear unit 195-196 serves to reverse the direction of rotation of the arm 112. The intermediate gear 217 rotates on the stud 219 anchored by a set screw in the gear housing side 200.

As said before, the lead screw 55 has suitable bearings inthe lugs 56a and 56b laterally projecting from the ends of the base 51. The reduced end 220 bearing in the lug 56a, together with the collar 221 secures the lead screw 55 against axial motion. The other and outer end ofthe lead screw 55 projects for `some distance beyond the outer lug 56";`

the extremity of said lead screw having mounted thereon the grooved hand-wheel 222 securable and slidably adjustable on said shaft bythe set screw 223 and soft metal disc, said hand-wheel being grooved to receive a belt 225 from the driving motor 226, or cord from a driving weight. The hand-wheel 222 has on the innerside a notched hub 227 adapted to engage the notched outer end 228 of the outer one of a pair of concentric tubes 229 and 230 surrounding that part of the lead screw coming between the lug 56b and the handwheel 222, the inner tube 229 being secured by its flange 231 and the screws 232 to the side of the bearing lug 56h. Between the two tubes 229 and 230 is a coating of asphalt 233, which serves to hinder the motion of one tube relative Vto the other. The amount of lthis hindering depends on the viscosity of the asphalt, and the viscosity of the asphalt depends on its temperature, which in turn depends on the amount of heat received from the electric lamp 234, the amount of heat received depending on the nearness of the lamp or adjustment of its flexible support, or by the degree of interposition of the shade rotatable on the lamp socket, or by the current in the lamp 234 as modified by a rheostat;

The lead screw has two threads 187 and 239, the coarser thread 187, as said before, making of the lead screw practically a long spiral pinion and being operatively connected to the`wormgear 141 to drive the arm 112, carrying the abrasive 115. The finer thread 239 of the lead screw is, through engagement with the split nut 57, used to move the carriage along the base 51. The two halves of the split nut 57 are in the form of U-shaped members 57a and 57", which are swivelly secured by the pins 240 through the extremities of the U limbs to the lug 241 projecting from the end of the carriage 54. rlhe two halves 57"L and 57b of the split nut 57 are kept in threaded engagement with the lead screw 55 by means of the spiral spring 242 hooked over the two screws 243, a screw being in each half on the split nut 57. To throw the split nut 57 out of engagement with the lead screw 55 there is provided the conical knurled nut 244 threaded onto the cap screw 245, the latter being fixedly threaded into the lug 241; entrance thereto for the cap screw 245 being secured through the hole 246 made up of the juxtaposition of two semicircular grooves in the near limbs of the U-shaped members 57a and 57h. By turning the conical knurled nut 244 to the right it is evident that it will advance into the hole and separate the two halves of the split nut 57 and throw them out of engagement with the lead screw 55.

On the lead screw 55 there is provided a. similar conical nut or conical bushing 247 for the purpose of automatically throwing the split nut 57 out of engagement with the lead screw 55. A short portion of the thread in the near side of the split nut is bored out and the corner of the hole slightly enlarged to furnish easy entrance to the point of the conical nut 247. rlhe nut is secured by the thumbscrew 249. This conical nut servesas an automatic stop to limit the motion of the carriage 54. By securing the conical nut 247, in any desired position on the lead screw the carriage 54, will automatically stop when the split nut- 57 comes into engagement with the conical nut 247 although the lead screw itself continues to turn.

Provision. is made for a non-positive advancement of the carriage by means of a stranded wire cord 261, one end being secured by the screw 262 to the carriage 54, the cord extending therefrom through the hole in the block 263 around the pulley 264 pivoted in the slotted end of the block 263, thence at es to its former direction right around the l ibe the end of the cord being to the t Y Ilhe screv 265. By pulley into notched engagelh the ube 230, and with the split ement with the lead screw pulley 222 by the motor the cord 261 and move to the eommutator. the split nut 5T out K cut vith 'the lea'l screw 55, the set screw 2113 in the hub o'l the hand-Wheel may oe backed oli and the hand-Wheel allowed to re ve on the end ot the lead screw as a ndle, The movement oit the carriage may be hindered the asphalt alone, as in the ivay given, or by the oil pump alone or by lvoth together. lith the use of a stranded ivii'e Cord 'to give a direct pull to he carriage the viscosity ot the asphalt can generally be made low enough. to give much speed to the carriage as is desired. 'It the is set up while tee hub 227 set-screw 22o is still in notched engagement with the tube 230 tho hindering effect ot the oil pump is added to that ot the asphalt to any amount desired by properly regulating the discharge to restrict the discharge of the oil. lbf it is desire(v to out out th asphalt hindering means when the carriage is moved by a di* rect pull, the screws 282 may be removed, thus allowing the inner tube 22) to rotate with the outer tube.

To support the lead screw there is y." mvo-d step 267, an extension of the block 268, the latter being attached by the screws y underside of the lug` 216" projectom the end oit the carriage This intended to keep the lead screw i om sorineing out et mosh With the gear he split nut 57 is not in engagehe lead screw and consequently forming incidental support to i the abrasive member there e hollow stud 272 forming a n 112 but insulated from the ed bore in the main part oi 1in the bore the split met-al hin the metal tube 1s the 1n` r l cemented thereto. lVithin :l 7* ube 274` is the tlrn split metal insulating Washer is the proi L sions in the split tube 2.73.

The part ot the stud 272 extending beyond the end of the main part of arm 112 has a square external thread 280. @n tais threaded part is an accurately fitting bushing 281 slidably keyed to the stud 272 by hey 282. The bushing 281 has a square external thread, but no internal thread. Threaded on the extremo end ot the stud 272 is the nut 283 circmnt'erentially grooved at 284 to receive one end of the spiral spring 285, the other end ot the spring 285 abutting on the end 01' the bushing 281. Between the other end of bushing 281 and the main part ot arm 112 is the spring 285. The purpose o1 the bushing and springs is to give a slight axial movement ot relief to the abrasive when a commutator having both deep ruts and end play is being trued up, thus prevent-ing the abrasive member .trom being caught in a rut and broken er having the active end saeared olf by the ani al movement of' the commutator. Generally there is no necessity to take precautions against end play, so that a split bushing may be used instead of the sliding bushing` 281; or the clamp 28G-288L or abrasive wheel 287 may be secured directly to the stud 272. By screwing up the lmurled nut 83 till it abuts against the end of the bushing 281 and entirely compresses spring 285fL the axial movement of the bushing 28' and therefore of the abrasive member 115 or 287, relative to the main part ot' arm 112 may be prevented. Betere assemblage these springs 285 and 285a should preferably be put into a state of partialcompression, the tivo Washers and the attaching chains serving to keep the spring partially compressed, but offering no hindrance to further compression by the abrasive when a combination of an engaging rut and end play of 'the armature give an axial movement to the abrasive independent of the rest of the apparatus.

The bushing 281 is provided also with an externa-l keyway 288, Figure 8, which, together with the thread 288, made use of when, instead of an abrasive block, an abrasive wheel 287 is used as the abrasive member. T his keyivay 288, an engaging key and a complementary leyivay in the collar 291 (as seen in Figure 11) serve to prevent the collar 291 from rotating on the bushing 281, and therefore diminish the possibility of the abrasive Wheel 287 getting loose and rotating on the bushing 281 after the said abrasive Wheel has been tightly clamped against the face of the collar 291 by the nuts 292.

Surrounding the main part of the arm 112, that overhangs the commutator when in operation, is a plurality of telescopic insulating sleeves 2193"*295b made of such material as libre or Herkolite. The object of the insulating sleeves is to diminish the possibility ot the arm 112 being the cause et a ground or short circuit on the commutator, Il' holes are drilled in the er d of the insulating sleeve 293aN for the purpose of inserting the counter sunk set screws 27 9 or for inserting a wrench, then a short section of insulating sleeve 293c is used to cover up the holes to prevent the possibility ofV current getting into the arm through these openings. The insulating washer 295 insulates the end ot the main part ot arm 112.

When the abrasive member is in form of an abrasive block a double member clamp 286- 286a as shown in Figure 8, is used to secure the abrasive block 115, to the stud 272. One end of the clamp member 286 is circular and is clamped by the cap screws 297 around the slidable bushing 281 or around av substituted split bushing or varound the stud 272, the latter two arrangements somewhat diminishing the chance ot vibration or chattering et the abrasive member. The other clamp member 286a is U-shaped, and, by -the cap screws 298 is clamped around the abrasive block 115. Strips of ibrous material 299 cemented to the extreme ends of the limbs oi the ael-shaped clamping member 286, serve to soften and distribute the gripping stress of the clamping member on the abrasive member 115, and at the same time to bring the gripping contact line as near as possible to the active end of the abrasive member 115. insulating sheets 300 and 300a of ibre or Herkolite protect to a considerable extent the accidental Contact of the clamp with a charged part ot the electric machine. @ver the head of the cap screw 298 is an insulating cap 301 with a threaded stem 302 integral with the cap and screwed into the threaded hole in the head of the cap screw. The cap 3011 is threaded onto the opposite end of the cap screw 298.

In Figures 1, 2 and 3 are shown means 'tor stopping the motion of the carriage after a predetermined travel. frs lshown in Figure 3 a clamp 332 is attached to the dovetail Vtongue 53 of the base 51; the clamp 332 being adjustable to di'llerent positions along the base 51 and being adapted to be secured in any position by means of the cap screw 332% At the upper side of the clamp 332 is a push button 333 in position to be struck and operated by the carriage or some partv attachee thereto or prominently projecting therefrom, such as the bearing block 62. Operation ot' the push button 333 breaks the current in the holding magnet coil 333 trips the circuit breaker 3331 and cuts ott current from the motor 226 driving the `pulley 222. 1n case the push button 333 should fail to function the bearing block 62 after a very small. additional movement strikes the clamp 332 bringing` the carriage 54 to a halt. Although in this case the current may not be cut ol from the' motor, the resistance in the rheostat 333C is so large that the. motor 226 can be stalled indefinitely without harm.

To limit the movement of the cross-feed slide, there is provided an offset bracket 361,

the lower end 362 thereof being attached by the cap screws 363 to the tace ot the carriage 54 and the other end 364 apertured to slidingly receive the body oi the cap screw 366 tixedly threaded into the cross-feed slide 59. The limit of the movement in either direction of the cross-feed slide will be determined by adjustment of the knurled nuts 367 in relation to the bracket end 364.

Means of limiting the rotation of the arm 112 include a stud 371 with its lower end threaded into the cross-feed slide 59. Splined on the said stud is the split clamping block 372, adjustable and securable on said stud by the knurled thumb-screw 373. @ne end of the block 372 overhangs the rod 184, and in this end is the knurled-headed temper screw 374 positioned vertically over the center of the rod 184. 1t is evident that when the rod strikes the temper screw 374 it will come to a stop, and consequently also the clamp 146 and the arm 112 to which the clamp 146 is secured. Adjustment of the clamp 146 on the arm 112 with reference to the distance ot the rod 184 from the temper screw 374 will permit a greater range to the rotation of the arm 112 Another means of limiting the rotation of the arm 112 is provided by the limit bar 375 secured to the top of the bearing block 111 by the screws 376 and 377, on `the latter ot which the said bar may swivel slightly. When the set screw 124 in the collar 123 strikes the limit bar 375, the rotation of the arm 112 is halted. By adjusting the position of the collar rotatively any degree of rotation of the arm 112 not greater than one complete revolution can be secured.

Current for the motor 226 is supplied from mains 334 and 335, through switch 336 and fuses 337. From one pole of the switch, say the positive, the current passes by the wire 338 to the circuit breaker 333". From the circuit brea rer 333b three' wires lead. Current passes by one of these wires to the rheostat thence by wire 342 to the reversing switch 343, thence by wire 344 or 344a to the motor armature 345. From the circuit breaker 333b a second wire 346 leads to one terminal 347 of the motor ield 348. A third part of the current passes through the retaining magnet coil 33a thence by wire 350 to the pushl botton lrom the negative pole ot the switch 336 three wires lead. Current passes by one of these wires 351 to the reversing switch 343, thence by either wire 344a or wire 344 to the motor armature 345. A second wire 353 leads to the terminal 354 of the motor tield 348. A third wire 355 leads to the push but-ton 333.

The asphalt between the tubes 116 and 117 used to hinder the motion of the arm 112 may lose its eilect either from a high temperature or from a low temperature and excessive strain. This has been explained at length in the case of the asphalt used to hinder the inotion of the feed-screw of the cross-feed slide. To take care of this contingency in the case of the arm 112 there is provided a simple clock mechanism 37 7d with its driving wheel 377 geared to the worm-gear 141 that drives the arm 112. From the clock escapement there extends vertically the rod 37 7i to which is attached the horizontal arm 377 g bearing the adjustable weights 377], the distance of which from the rod 37 7f determines the rate of movement of the clock mechanism and therefore of the rate of rotation of the arm 112 and therefore of the rate of movement of the abrasive 115 towards the commutator. The clock escapement is preferably of the kind that will function when the driving wheel rotates in either direction.

If the clock escapement is the kind that will opera te only in a forward direction and locks in the other direction, then we would have positive hindered (delayed) advancement of the abrasive.

To provide for the possibility that the asphalt hindering the motion of the leadscrew 55 may lose its hindering eect there is a small oil pump 377 operatively connected to the lead-screw 55 at its inner end, with a valve 3371 to regulate the rate of discharge of the oil and therefore the rate of rotation of the lead-screw and therefore of the carriage 541 and therefore the axial movement of the abrasive 115. Where a positive movement of the carriage with comparatively high speed is desired, thus necessitating the use of the .tine thread of the lead-screw with comparatively high rate of rotation of the lead-screw, the loil pump may be used as a hindering means in preference to comparatively soft aS- phalt, which might be more or less erratic in its hindering effect when very soft.

In view of the foregoing the operation of the truing device is readily understood. As explained before, the apparatus, in preparation for grinding a commutator, is mounted on an offset fiat bar beam secured by studs in the bearing box of the electric machine. The base of the apparatus is secured to the lower step of said offset flat bar beam. Further security is attained against vibration by the use of jack-screws supporting the base of the apparatus and the flat bar beam, and by turn-buckle guy rods or chains running from the flat bar beam and the base of the apparatus to the base of the pillow-block. The base of the apparatus is mounted parallel to the axis of the commutator except in the case where it is desired to advance the abrasive towards the commutator by having the base of the apparatus slightly out of parallelism with the axis of the commutator.

The lead screw 55 is then turned by hand or by a motor until the abrasive member reaches the inner edge of the commutator. A clamp l1111 is then clamped across the ways of the base and against the inner end of the carriage to serve as an automatic stop thereafter to limit the inward movement of the carriage.

The lead screw is then turned in the other direction until the abrasive member reaches the outer limit of its travel.. If there is a shrink ring in the middle of the commutator' this will determine the outer limit of travel while the inner half of the con'nnutator is being trued up. The several safety devices to limit they outer 'travel of the carriage are now adjusted; these include the clamp 332, the push but-ton 333 attached thereto, and the conical bushing 2117 for throwing the split nut 57 out of engagement with the lead screw 55. The endeavor should be to so regulate the push button by adjustin its ptmition on the clamp that it will function to thro w out the circuit breaker slightly before the carriage is compelled` to stop by the clamp or conical bushing 217.

By loosening up the clamp 122, the arm 112 can be rotated rvithout the interference of the asphalt hindering means.

The carriage is then run toward the inner end of the commutator again till it strikes the clamp 441 and stops. During these toand-i'ro movements of the carriage. the

rlieostat 333c should be manipulated a bit and the position of the rheostat handle noted that will give a few pounds of pull on the pulley 222.

Clamps 122 and 75 are loosened, freeing respectively the arm 112 and the feed screw G1 from the effects of the asphalt hindering means. By rotation of the arm 112 or movenient of the cross-feed slide the abrasive member is brought into contact with the commutator. If the abrasive member is an abrasive block the endeavor should be to have the abrasife make contact with the commutator, not in a radial line, but at a substantial angle to a radial line, say 450 with a radial line, as there will be less chance of the abrasive chattering in this latter case. The abrasive block should preferably be in a trailing position; that is, the commutator should leave from the acute angle of the abrasive l'ileek. If the electric machine runs in both directions a still larger' angle is desirable.

For a time the abrasive may be fed towards the commutator without any axial movement, of the abrasive. rfhis feeding or advancement of the abrasive towards the commutator may be made by the rotation of the arm 112 by means of the beam 153 and weight 154-. The clamp 122 is tightened up, thus clamping the tube 117 to the collar 123 on the arm 112. The lamp 125 is now brought into use if necessary to soften up or lower the viscosity of the asphalt 11S between the tubes 116 and 117, thus permitting a slow rotation of the arm 112. How fast the arm 112 will rotate ant advance the abrasive towards the commutator will depend on the magnitude of the actuating Weight 154, its leverage on the beam 153 as Well as on the viscosity of the asphalt; also on the grade of the abrasive block, the area of contact with the'commutator and the condition of the contact end. TW here there is little reason for speed in finishing the job, the abrasive block may be advanced towards the commutator no more than 1/64 of an inch an hour. By advancing the abrasive very slowly it is used much more eiiciently than in ordinary grinding practice, say two to five times more efciently-referring to the weight of copper ground olf for each unit of weight of abrasive material consumed. It is generally advisable, at least at first, to use only the softer grades of abrasive-say grades F, G, and lvl, acco 'ding to the grading system used by ino-st manufacturers of abrasives. A soft abrasive is not so liable to pick up copper, and then cease to cut-particularly when the force advancing the abrasive is small. And a small. advancing force is desirable not only for economy of abrasive material, as has been said, but also for lessening the chance of vibration in the apparatusparticularly when the foundation for the grinding apparatus is not as firm as it might be. Generally the abrasive bloclr should be as short as possible so that the active end of the abrasive block will be as close as possible to the arm 112, so as to lessen the chance of vibration.

In the operation of the apparatus as just eX- plained both friction hindering` means and viscous substance hindering means are inl operation to hinder the motion of the arm 112. r1`he beam 153 bearing the weight 154 has been in a position other than at right angles to the arm 112, so that there is considerable friction of collar 142 on the end of the bearing block to hinder the rotation of the arm 112.

To operate with asphalt hindering` means alone, all that is necessary to do is to swing the beam 153 around till it is at right angles to the arm 112, thus eliminatingl the tipping of the collar 142 against the end of the bearing block 111 and consequently the friction of the collar against the end of the bearing block.

To operate with a friction hindering effect only the clamp 122 is loosened, thus eliminating the asphalt hindering edect. To find the best position for the beam 153 the beam is swung around from an initial position parallel to the arm 112 till the arm 112 begins to move, the angular position of the beam with reference to the arm 112 being' noted on the gauge 160. A few degrees beyond this will generally be the most desirable position for the beam 153, rThe amount of the weight 154 or its leverage will not alter the relation between the rotary effort and the friction hindering elfect if this angle is not changed and if the arm 112 turns freely in the bearing block 111. There will be a slight to-and-fro y rotary movementl to the arm 112 because the abrasive bloclr will follow up the flat spots in the commutator. lf the commutator is in bad shapeas with flat spots blackened up from hiO'h mica-and immediate improvement is wanted, then friction hindering means should be used alone to advance the abrasive block radially. After allowing the abrasive to act for a time at the inner end of the commutator the aXial travel of the abrasive block may start, using the stranded wire cord 261 instead of the lead screw to move the carriage. Non-positive means of advancing the carriage are somewhat more desirable in this case, with ridges and ruts assumed to be in the connnutator, than the positive means through the use of the lead screw. 1f the edge of the abrasive should be in contact with the side of a ridge a sudden starting of end play might break off the abrasive block unless a retrograde movement of the carriage is possible as is the case with a non-positive means such as the cord 261. While the slidable bushing 231 and the springs 285 and 2850L are intended to take care of end play, the possibility of a backward movement of the carriage gives additional securitythat no harm will be done by end play.

Descriptions of other methods of operating the device follow. l/Vhere there is the necessity for the arm 112 to clear a shrink ring in the middle of the commutator or a commutator fan guard on the outer end of the commutator, the active end of the abrasive block may have to be from four to six inches from the center of the arm 112. Abrasive wheels should be small as possible in diameter to minimize chance of vibration, Thin and narrow abrasive blocks may be used to avoid vibrationV when the foundation of the apparatus is not very secure.

To limit the advancement of the abrasive block the temper screw 374 is adjusted, allowing the abrasive block to adva ice, say 1/3 of an inch before the rotation of the arm 112, is brought to a halt.

During this process the rod 184 is out of operative engagement with the round bar guide 174,'and the worm 206 out of engagement with the worm wheel 141.

Having now cut a shallow groove in the inner end of the commutator, the next strip is to carry a traversing cut across the commutator. Preliminary to this the rod 184 is put into operative engagement with the round bar guide 17 4, the grooved hand-wheel 222 belted to the motor, into notched engagement with the tube 230 and the split nut 57 into engagement with the lead screw 55, and the stranded wire cord 261 removed from operative connection between the carriage 54 and the outer tube 230. If necessary the lamp 234 is used to modify the viscosity of the asphalt between the tubes 229 and 230. rllhe round bar guide is then given sufficient inclination by adjustment of its outer end by means of the thumb-screw 175 to cause the abrasive to wear away, say 1/2 inch, while it is making the traversing, or axial cut, along the length of the commutator. lVhen adjusting the end of the round bar guide, reference may be had to the two gauges 1781L andv 178b adjacent to the slot 176 in the strap 177. The gauge on the right 178 indicates the number of degrees of rotation of the arm 112 for one footof travel of the carriage 54. The gauge on the left 178b indicates the number of inches of wear of the abrasive block for one foot of travel of the carriage. In marking this latter gauge the average length of the abrasive block and its clamp from the center of the arm 112 to the active end of the abrasive is assumed to be five inches; and the average inclination of the abrasive block with a radius is assumed to be 450. IVhen the length of the abrasive block and its clamp, and the angle it makes with a radius vary from these assumed conditions, allowances can be made accordingly.

In getting rid of the copper chips and abrasive dust an exhaust fan may be made use of (if such a fan is available) the suction hose being connected to the outer end of the hol low arm 112, the suction intake being through thehollowstud 272. To facilitate the entrance of the grinding dbris into the hollow stud 272, a sheet of asbestos cloth may be folded around the abrasive block 115 and the stud 272 to form a common hood to confine the dbris therein as well as form a passageway to the hollow stud. If there is no exhaust fan at hand a gentle stream of air from the compressed air system may be allowed to play upon the abrasive block as near as possible to the inner end of the commutator, in order to drive the debris outward and keep it out of the eominutator risers. The compressed air hose may be attached to the hollow arm 112, the air striking defiectors as it leaves the hollow stud 272 which throw it against the abrasive block and drive the abrasive and copper dust away from the armature winding.

A simple compressed air ejector may be made out of a short piece of old rubber hose. Through a hole or slot near the middle of the short piece of rubber hose is inserted the nozef the compressed air hose, the nozzle ei;- tending` some inches up one branch of the short piece of rubber hose. f

How fast the carriage 54 will travel will depend partly on the viscosity of the asphalt betweenithe tubes 229 and 230 as modified b y the heat from the lamp 231i, partly on the torque of the motor 226 as regulated by the rheoetat 333, partly on the inclination of the round bar guide 17 t, as well as on the size and grade of the abrasive block itself and the condition of the commutator. If there are no .high ridges in the commutator the abrasive :may advance axially 1,/4 inet; te an inch er more an hour; if there are high ridges that have to be ground away from their sides to a considerable extent, and if it is desired to use the abrasive block as efficiently as possible, then the abrasive block may be advanced axially considerably less than 1/4 of an inch an hour. Generally when there are high ridges on a commutator a second cut will have to be taken7 so the first cut, or roughing cut, can be taken regardless of the possibility of vibration of the apparatus. In this case a hard abrasive block can be used and a greater torque put on the motor 226 by adjusting the rheostat 333C.

In the operation just described it was assumed that the brush-holder sets were far enough apart to permit the entrance between them of the abrasive block inclined at a suitable angle to a radius. However the brushholder sets may be so close together that the abrasive block has to be positioned on a radial line. In this case we are prohibited from rotating the arm to advance the abrasive block, being limited to either the use of the cross-feed slide or to setting up the apparatus with the base out of parallelism with the axis of the cemmutator; the former means being applicable to advancement of the abrasive radially with or without a coexisting axial travel ofthe aln'asive,wliile the latter mean sthe base of the apparatus out of parallelism with the axis of the commutator-is applicable to a radialadvanceme'nt of the abrasive only in coexistence with an axial advancement of the abrasive. It is possible of Course to use the cross-feed slide with the hose out of parallelism with the axis of the commutator.

With the abrasive block at the inner end of the commutator, we mayi lirst advance the abrasive radially without any axial Inovement, using for this purpose the cross-feed slide. To turn the feed-screw 61, the weight 78 with several turns of solder wire 77 around the hand-wheel is employed, utilizing if necessary the lamp 99 to lessen the viscosity of the asphalt 79 between tubes 71 and 72. The clamp 7 5 is tightened up, thus clamping the hub of hand-wheel 70 to the outer tube 72. Ono of the knurled nuts 367 is adjusted to set a li mit. say of 1/8 of an inch, to the advancement of the abrasive. During the operation just described the motor 226 is not in use. The motor 226, together with the other accessory means as previously described is now put into operation to drive the lead screw To permit the radial advancement of the abrasive while it is making its axial movement along the commutator, we may back ed' the knurled nut 367 that stopped the movement of the cross-feed slide, to the amount of, say one inch. Judgment is new usesL as to the proper weight to be applied to the hand wheel 7 G and the proper viscosity of the as pbalt 79 between tbe tubes 7l and, 72 to adf-

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