US2535997A - Cross-feed mechanism for grinding machines - Google Patents

Description

Dec. 26, 1950 I ETAL 2,535,997

CROSS-FEE OR GRINDING MACHINES Filed Dec. 5, 1946 1O Sheets-Sheet 1 10 Sheets-Sheet 2 H. ARTER ET AL CROSS-FEED MECHANISM FOR GRINDING MACHINES Dec. 26, 1950 Filed Dec. 5, 1946 Z Dec. 26, 1950 H. ARTER ETAL 2,535,997

CROSS-FEED MECHANISM FOR GRINDING MACHINES Filed D80. -5, 1946 1.0 Sheets-Sheet 5 F1 9. Cb.

Dec. 26, 1950 H. ARTER ETAL CROSS-FEED MECHANISM FOR GRINDING MACHINES 1O Sheets-Sheet 4 Filed Dec. 5; 1946 Dec. 26, 1950 H. ARTER ETAL CROSS-FEED MECHANISM FOR GRINDING MACHINES Filed Dec. 5, 1946 10 Sheets-Sheet 5 H. ARTER ETAL CROSS-FEED MECHANISM FOR GRINDING MACHINES Dec. 26, 1950 10 Sheets-Sheet 6 Filed Dec. 5, 1946 mm m m Dec. 26, 1950 H. ARTER ETAL 2,535,997

CROSS-FEED MECHANISM FOR GRINDING MACHINES Filed Dec. .5, 194a 1o Shets-Sheet "r Fig Dec. 26, 1950 H. ARTER m 2,535,997

CROSS-FEED MECHANISM FOR GRINDING MACHINES Filed Dec. 5, 1946 1o Sheets-Sheet a Dec. 26, 1950 H. ARTER EI'AL CROSS-FEED MECHANISM FOR GRINDING MACHINES Filed Deb. 5, 1946 10 Sheets-Sheet 9 CONSTANT SPEED 5 PHASE A-O MOTOR EQ U l PPED wifh BUlLT IN BRAKE and SOLENOID RELEASE 44- FAST 5 LOW De c. 26, 19 50 H. ARTER ETAL 2,535,997

CROSS-FEED MECHANISM FOR GRINDING MACHINES Filed Dec. 5, 1946 l0 Sheets-Sheet 10 E 115. THYMOTROL UNIT 5 6 6 67 fi x f P P' W 71 R R x v EN IN OUT OUT 5T 5 SLOW FA 7R WHEEL c2055 FEED PUSH Fave m FEED H/u. FOR our 5650 51.0w FAST Patented Dec. 26, 1950 UNITED STATES PATENT OFFICE CROSS-FEED MECHANISM FOR GRINDING MACHINES Application December 5, 1946, Serial No. 714,168

17 Claims. 1

In machines for grinding cylindrical surfaces on articles of work, the relative approaching and receding movements of the grinding wheel and the work piece are usually produced by the operation of a so-called cross-feed mechanism. Such a mechanism includes a hand wheel which is connected through suitable gearing to the wheel head or the work support so that rotation of said hand wheel relatively adjusts the wheel head and the work support toward or from each other. Usually the hand wheel, or a drum rotatable with it, is graduated to indicate the extent of these approaching and receding movements. Such graduations, however, are difficult to read, and in order to obtain a high degree of accuracy in the work produced, it is necessary to depend more upon micrometer measurements. of the work than on the hand wheel graduations.

Additional objections to mechanisms of this type are the fact that they are slow to operate, so that considerable time is required in making large changes in adjustment, and back-lash and torsional strains in the gearing and transmission mechanism also are potential sources of error.

The present invention aims to devise a crossfeed mechanism in which these objectionable features will be eliminated; which will be less laborious and more convenient for the workmen to operate, and in which a high degree of accuracy in the work produced can be easily and quickly achieved.

The nature of the invention will be readily understood from the following description when read in connection with the accompanying drawings, and the novel features will be particularl pointed out in the appended claims.

In the drawings,

Fig. l is an end view of a grinding machine embodying features of this invention;

Fig. 2 is a side elevation of parts of the adjusting mechanism provided by this invention, with the motor removed;

Fig. 3 is a vertical, sectional view taken approximately on the line 3-3, Fig. 2;

Fig. 4 is a. horizontal, sectional view through the casing of the indicator, the section being taken on the line 4- 1, Fig. 5;

Fig. 5 is a vertical, sectional view through the indicator casing, taken o the line 55, Fig. 4;

Fig. 6 is a plan view, with some parts in section showing the base on which the wheel head slides;

Fig. 7 is a vertical, sectional view through the wheel head and its supporting devices;

Fig. 8 is a vertical, sectional view taken substantially on the line 88, Fig. 10, showing a modified form of adjusting mechanism for the wheel head;

Fig. 9 is a sectional view on the line 99, Fig. 8;

Fig. 10 is a view, partly in side elevation and partly in section, on the line lO-l 9, Fig. 8;

Fig. 11 is a partial section of the controlling mechanism for the clutch;

Figs. 12 and 13 are wiring diagrams showing control circuits for the motors which supply power for producing the cross feeding movements of the wheel head;

Fig. 14 is a front elevation of a portion of the switch panel; and

Fig. 15 is a horizontal, sectional view showing those members which support the work for the grinding operation.

Referrin first to Fig. 1, the machine there shown is organized on similar lines to that illustrated in Patent No. 1,736,967 issued to one of the present applicants. That is, it comprises a grinding wheel 2 mounted in a wheel head 3 for rapid rotation around its own axis, and such rotation is produced by an electric motor 4 belted to the wheel shaft 5. The work pieces on which the wheel operates are held between work holders, at least one of which work holders is mounted to revolve around the axis of the shaft 6 and is driven as by the motor "I. In the foregoing respects the machine is similar to those common in the grinding machine industry.

In the normal operation of the machine the wheel head and the work holders must have some provision for relative movement toward andfrom each other, and this is most conveniently accomplished by moving the wheel head rather than the work holders. For this reason the head 3 is mounted on a base 8 which is adjustably bolted to a bed'H, the base being provided with guides Iii-Ill, Figs. 6 and 7, on which the wheel head is slidably mounted. A wear-piece H and gibs I2l2 cooperate with the guides 10 to support the wheel head in its operative position.

Provision is also made for adjusting the base 8 angularly in a horizontal plane about the pivot 53, Fig. 6, which is fixed in the bed piece 9. For this reason the top of the bed is machined accurately, and the adjusting movement is produced by pivoting a link l4, Figs. 1 and 6, to an arm integral with the base, and extending the threaded end of the link through a bracket l5 which is secured rigidly to a part of the machine frame or bed. Nuts iii-46 are threaded on this end portion of the link it so that by properly manipulating them the angular position of the base 8 may be adjusted at right angles to the axis of the work holders, or in some other de- 5 sired angularrela'tionship tothem; Several bolts ll extending tln'ougharcuate slots in ears, projecting from the margin of the base 8, as best shown in Fig. 6, serve to secure the base in its adjusted position on the bed 9. V 7 v 10 In this machine, as in that shown in the patent above mentioned, the grinding wheel 2 is mounted on an eccentric sleeve or quill which'is supported in bearings so that by oscillatin the quill, the wheel may be moved bodily while the wheel head remains stationary, and this arrangement is employed to move'the wheel into engagement with the work; hold it there for the desired length of time; and then to withdraw it While the work piece previouslyoperated upon is moved out" of grinding positionand another is indexeddnto position to 'be gr oi'lnd. And' this cycle of'bperationsis repeated on each work piece until some change in the character ofthese articlesof work makes" it necessary to change the relationship of the parts in someway. However, in initially'adjus' tingthe machine to a new" articlegf work, it is usually necessaryto move the "wheelhead 3 forward or backward in order to position the grinding wheel properly for 'eperatio'nbn thenewworkpiece. d

Important features of this inventionreside ina novel mechanism for producing this adjusting movement, bypower, but under close contro1 of the workrnanfi'Also; in anindicatingmeohanis operatively associated with thi adjusting-m eansfl to give ea ny readineasurements of the move ments of the'whee'l'hea'd and its wheel? d For this purpose a screw or screwthreaded shaft l8 is secured at one end in the baseil as shownjfcrexampl'e, in Figs. 6 and' l, and projectsrearwardly' f'or a substantial distance be yond the end of the main body of the base. Threaded'on it is a nut 20, Figi'fi; having an'ex tended' bearing in a braclgetll, Figs. 1; 2 and 3, which is bolted securely to the rear end of the wheel head and, to all intents and purposes, 'ex cept'for convenienoeof manufacture, forms a partof said head. The nut can revolve freely on the stationaryscr'ew 18' but is held'a'gainst axial movement relatively to the'wheelhead Conse quently,' rotationof thisjnut willoperateon the screw I8 to move the entire w'heu eaaasse bly toward and from the work supporting mem bers. v v

Such rotation prejferablyis"produced by power as, forexa'mple',"b'y the electric motor 22 whichisboltdi'to one' side' of the bracket 2 i. In the em bodim'entpi theiriven'tion*illustrated-in Figs. 2 and- 3, the m'otoris of the direct current, reto versibl'e, variable Speedtype, arranged to be controlled entirely from alswitchpanelatthe front of the machine"tl miug'h push buttonsQor other easily operable switches, as will later be 'de" scribed; 1

This motor is connected with then'utiil by a reductiongearingl'which, as shown in" Figs' 2 and 3, comprisesa worm 23 fastio n the motor shaft 2 and meshing w-ith a'worm' wheel 25 fast'on another w0rnisha'ft26 ori'which a worln'i'? is rigidly securedor is made integral therewithi The nut 29 has the'form'of a 'wormf g'ear; or includes a sectibnwhich' consists of a worm gear, meshing with the worm 2i. Consequently, the motor 22, when energized, *drive'sthe n'utat a speed Very much slower than that of the motor shaft, the ratio of the speed reduction being determined by design. A suitable ratio is in the neighborhood of forty to one, so that one revolution of the worm moves the wheel head .005 inch. A

The worm shaft 255 is mounted in antifriction bearingswhich' support it against end thrust, as well as radially, and an important advantage of this speed-reducing arrangement is the fact that it lends itself readily to the dual function of adjusting the wheel head and also of operating an indicator. For this purpose a dial casing having'a'long tubular stem 28 and a head 30 is secured to'the top o'fthe bracket 2! and extends upward therefrom. Mounted in this casing is a vertical shaft 3! which is connected to the shaft 26 by a collar 26' fast onthe upper end of the shaft 26, another collar 3| fast on, or forming an enlargement of, the lower end of the shaft 3!, and a pin 32 fast in one of these collars but projecting into a'hole' 'in the'other j An extension 26''; Fig; 5, of the shaft'zii projects into a hole in the col-' lar 3i and centers the two shafts 26 and 3| with each other. "Withthisarrangement, therefore, any rotative ixiovernentbf the shaft 23 is trans-" mitted accuratel to the indicator 'shaft3 r.

Keyed to the'shaft 31 is a disk 33, the peripheral surface'o'f which is suitably graduated-in this= casein tenths of thousandths ofan inch. "Part of the pe'riphery of this dial, facing toward the front of the machine, is'exposed througha window 34, Figs.3 and'4. I

Immediately a'bove"th'e dial 33 is another dial and the two: are connectedtogether through a reductiongearing' having "a ratiojinthis particu lar case, 'oftento onefThat is, a pinion'iifi, Figs. 4. and 5; on thau'pper endbf the dial shaft 3i,

meshes'with, and'drives' 'a'gear 31 revolving on a stub shaft 38, and another pinion w revolving with the gear 31 meshes with a gear M which is pressed'on tothe upper end 'of a bushing 42 with whichthedialj'fifi also has a pressed fit. The peripheral face of this dial 35 is graduated in thousandths of an inch;

In using this mechanism, and assuming, for

instance, thata workmanis operating the rnachine "to produce a ground surfaceof a given diameter on a certain pieceof work, and he finds, upon'measuring a'sample piece, that it is three ten-thousandths of an inch'toolarga he "can make'the required change in the position of his grinding wheel merely by pushing the proper button 'to start up theadjusting'mechanism and stopping the motor again when the desired c'ormotion has been made. And he can read the d greeof adjustment, while so produced, very easily and accurately on the dial33fi' In fact, he can ven split a ten -thousandth of an inch with this j mechanism, and he can do 'so with little effort because all he has to do is to operate" one or two push {buttons and read the results on the dial. This'arrangement, therefore, enables the operator to make his adjustments of the grinding wheel without a great deal of labor.

While the quill above re'ferred to is highly usei ful inmovingfthe grinding-wheel toward and' from the work between fixed limits, the cross-feed is valuable in moving'the whole head assembly, both for the purpose of correcting the position of the Wheel in its relation to the work, and also in 7 making the initial adjustments required in set ting up for a different work piece.

If the over-all movement of the wheel head required in making any adjustment is large, say several inches, the operator can adjust the speed of the motor 22 to its maximum, or thereabouts, until the greater part of the adjusting movement has been produced, and then slow it down to a very low speed while he brings the wheel to ex actly the position desired.

The reduction gearing is enclosed in a casing, parts of which are integral with the bracket 21, and it holds ample lubricating material for the gears. This material may be supplied through the oil cup 43, Fig. 2.

Figs. 8, 9 and 10 illustrate a modification of the mechanism for driving the nut 20 which differs primarily from the arrangement above described in that it employs a constant speed electric motor and the mechanism for transmitting motion from this motor to the nut includes a twospeed gearing. Referring first to Fig. 8, the shaft l8, nut 20, and the driving worm 2] for the nut, are the same as in the construction earlier described. The motor 44 is suppported vertically on a bracket 2! which takes the place of the bracket 2|, shown in Fig. 1. Fast on the shaft 45 of this motor is a worm 46, Fig. 10, driving a worm wheel 41 which revolves freely around the shaft 48. At the right-hand end, Fig. 8, of this shaft it carries a worm 49 driving a worm wheel 50 fast on the lower end of the worm shaft 25, Fig. 8. Consequently, one chain of driving connections between the motor and the worm 27 come through the shaft 48 in this way.

Another chain of driving mechanism includes a spur gear 5|, Figs. 8 and 10, fast on the motor shaft and driving a pinion 52 on a vertical shaft 53. A spiral gear 54, Fig. 9, fast on this shaft drives a cooperating gear 55 mounted to revolve around the shaft 48. Consequently, when the latter gear is connected with the shaft 48 to drive it, it also operates through the connections above described to revolve the nut 20.

Between these two gears 41 and 55, mounted to revolve around the shaft 48, is a clutch 56 slidable on said shaft but splined to it, and operable to connect these gears selectively to the shaft. Preferably this clutch is arranged to be operated by a lever 59 fast on the rock shaft 58 and another lever 51 also secured on said rock shaft and pivoted to the plunger of a solenoid 60, Figs. 10 and 11, the solenoid serving to shift the clutch in one direction While the spring 6! moves it in the opposite direction.

With this arrangement, therefore, the motor may be made to drive the wheel head either at high or low speed, as desired. Control of the motor is accomplished through a push button arrangement, as in the construction above described, and by using a reversing switch, the mechanism may be arranged to drive the wheelhead in either direction. For example, if an 1800 R. P. M. motor is used, the comiections with the switch controlling it should be so arranged that the solenoid for the high speed gearing will be connected in parallel with the switch and will shift the clutch to bring the high speed gearing into action simultaneously with de-energizing the solenoid. When the slow speed button is pushed, the solenoid then will not be in circuit, and the clutch will be shifted back to its low speed condition by the spring 65. The low speed gearing drive may, in a typical instance, have a rate of approximately two thousand to one, while the high speed drive may be in the neighborhood of forty to one.

Fig. 12 is a wiring diagram of a control system for use with the driving mechanism just described, the mechanical parts, as well as the wiring, being shown diagrammatically. As there illustrated, the motor 44 is of the three-phase constant speed type equipped with a built-in brake which is automatically released by a solenoid when power is on the motor. It is connected with the power supply lines 62 through two switches or contactors indicated at A and B, respectively. They are arranged to be electromagnetically operated by coils or solenoid C and D, respectively, but springs connected to the plungers of these solenoids normally hold the switches opened. These switches A and B are, in turn, controlled by push buttons, or pull and push switches, indicated at E and F, and these preferably, also, are spring-controlled so that when either switch is not held in its in or out position it will be returned automatically to a neutral position. In the latter position both coils C and D are de-energized, the switches A and B consequently open, and the motor is de-energized. Preferably, also, these manually operated push buttons or switches E and F are so interlocked, in ways well understood in this art, that it is impossible for both switches A and B to be closed at the same time.

Assumin that the operator wishes to move the grinding wheel 2 toward the work W at a fast rate, he will push the switch F to its in position, where the switch cross-bar will connect the contacts a, b and 0 together. This, as will readily be observed, connects both the coil C and the solenoid 60 across one phase of the supply line. Consequently, the motor is started up and simultaneously the clutch is shifted into the position shown in Fig. 12 where it connects the driving shaft of the motor through the gears 5i and pinion G corresponding, in a general way, to the high speed drive above described, to the shaft H and the gear I fast on it, to the feed screw nut 20. This moves the feed screw is and, hence, the entire wheel head assembly inwardly toward the work piece W.

When it is desired to withdraw the wheel head at a high rate of speed, the fast switch F is pulled out, which has the effect of de-energizing the coil C, energizing the opposite coil D, and maintaining the solenoid 68 energized. Thus the direction of rotation of the motor is reversed, due to the fact that the switch A is opened and the switch B is closed. The wheel head will continue to be withdrawn until the fast switch F is moved to its neutral position.

When it is desired to use the slow-motion feed, the switch F remains in neutral and the slow switch E is operated. It will be observed that the contacts of this switch are cross-connected with those of the fast switch so that when it is pushed in, the motor is started up exactly as be-- fore. However, there are no connections between the slow switch E and the solenoid 68 so that at this time the spring 5! holds the clutch 55 in engagement with the pinion 46 loose on the motor shaft. This pinion meshes with the large pinion I and thus revolves the feed nut 20 at a very slow speed. In other respects the action of the whel headfiin or outzimavbe produced" at eithera highfor low-speed;boththese'speeds, however,'being fixed" and predetermined. *This is a 'disadvanta-gein many cases and it is preferableg there'fore; to use a direct -current motor because its speed of operation can be controlled by variations in the voltage applied to it; "A J practical difficulty in accomplishingthis result,

however, is the'fact that direct'current is rarely available in a manu'facturingplant. Accordingly,

in order to make it convenient for a customer to use the machine equipped as shown in Figs. 1 to 6,

inclusive, it has been necessary to devise a special control system to satisfy the-practical conditions as theyexist in almost'any machine shop.

Fig. 13 illustrates such a system provided by this inventionl As there shown diagrammatically'; the-motor 22 is connected to the nut and the feed screw shaftlB in a manner to function'as illustratedi'n Fig. 3. Alternating current supplied by the line 64 is ledinto'a rectifying unit 'of'the electronictype' shown at 65; The par ticular unit there illustrated is that known cornmercia-lly as the -Thymotrol rectifier manufactured and sold by the General Electric Company; It delivers direct current to the terminals 66 told, inclusive.

The first two of these terminals are connected by condu'ctorsto the shuntfield H of the motor 22, butthe speed of this'motor is controlled by varying the voltage across the motor brushes,

while its direction of rotationis controlled by the reversingswitch R-R. Conductors connect this switch 1 with the motor armature 22, and an interpole fieldlZ and a seriesfieldlS are connected' in series in the armature circuit. -While the re'versing'switch is connected directly to the terminals 59 and 19, the voltage maintained across these terminals is controlled by the vari-' ablev'olt'age applied'at the terminal-68. This voltageissupplied by either of two potentiometers P and P, connected'in parallel across the line fed by the terminals '65 and El and they include pivoted contact arms M and M, respectively; so

that the position of these arms determines the value of the voltage at the terminal 63 which,

will be slow,"b"ut because the motor is compound- Wound," its to que Will beample to perform 'the duty' required of it, with the result that it will operate through the reduction gearingshown in Fig. 3 to move thewheel head inwardly at a very slow rate. 7

Both the-switches "l4 and'l5 preferably are spring-controlled, as above explained in connec tion with the'switches E and F, so that they return to their neutral or open positions as soon as released. Consequently, when the switch 14 is released, the'motor stops and the'grinding wheel remains in the position to which it has been adjusted, the opening of the switch '14 also deenergi'zing'the coil 76 of the reverse switch and causing it to return to its normally' open position, as'in" the systempreviously described.

If, now, the-slow switch 14 is pulled out, it will close a' circuit through thecoil ll for the reversing l the motor runs at "a correspondingly higher speed.

Either the slow'or the fast speed of the motor may be adjusted up or down from" the values above assumed by moving the potentiometer arms M or M, and in this way' a wide variation in the rate of movement of the wheel head toward or i from the work maybe produced at any time.

This extraordinary flexibility is very valuable in a machine shop'handlinga great variety of work, i

and it is obtainablewiththe construction shown by apparatus which is very reliable, relatively simple, and not liable to get out of order. For

' these reasonsthiS' direct current drive is much as just stated, "controls'the' 'voltage across the terminals 69 and H1. The application to the motor of either of the voltages so' produced at any instant is controlled by twd'push and pull switches l6 and 55, respectively, operating in conjunction withthe reversingswitch RR;

Assuming,'for example, that there is a constant voltage of 240 across the terminals 66 and 6?, the

voltage of the former being zerofand that'the arms M and M are so adjusted that the voltage delivered at the pivotal point of the arm M is 40,

' eithermotor preferably are mounted on a switch whilethat at the corresponding point of the arm M is 200; these two control voltagesmay-be con ducted "selectively-to the Thymotrol terminal E58 by tl'ieoperation of the'slowor fast switch i4 or 15, as desired.

Assuming that theoperator desires to move the wheel head 3 toward the work W at a slow speed, he pushes the-slow speed push switch or button M in so that its upper cross-bar completes a circuit from the switcharm M to the Thymotrol terminal-68. At the same time the lower cross-bar of the switch M closes a circuit throughthe actu ating solenoid i6, thusclosing the section R of the reversing switch. This startsthe motor 22 in operation at a rateof speed determined by the low voltage of delivered across the terminals 69 and 10. Assuming that the motor 22 is built for a normal voltage of 240; the-speed necessarily preferred to the alternating current system'above described."

The motor 22 when driven by a Thymotrol unit'provides a regenerative braking. That is,

when the current is cut'ofi, the momentum tendsto keep the motor running, but the rotation of the armature then changes the motor into a generator which quickly brings it to a stop. No other type of brake is necessary with this arrangement.

The switches for controlling the operation of panel which also contains switches, levers, -or other elements for'controlling other functions of the machine. A portion of such a panel is illustrated at an in Fig; 14, and the knobs or handles of the switches it and T5 are there shown,in their normal positions; on the panel. Also mounted on this p'aneLbut preferably not so readily acces-' sible, are the adjustable arms for the potentiometers P and P, and all ofthe contros are located in some position such that the operator can reach them alleasily, although such positions may be relatively remote from the respective motors or other instrumentalitieswhich they control. particular, the panel should be so positioned that the operator can readily see-the indicator dials while he manipulates the control switches.

The means above referred to forsupporting the work for the grinding operationmay be of any suitable character. illustratedi-n Fig. 15 wherethe revolving centering devices 78-48 carried by the respectiveshafts -A typical arrangement is G--6 are mounted for relative movement toward and from each other to release the work piece while another is placed in position to be operated upon. These operations usually are performed automatically.

In this connection it should be pointed out that the power for driving the indicator is taken from the reduction gearing at the point of lowest speed of this mechanism, namely, the shaft 26. Con

sequently, any error due to back-lash is substan- 1 tially eliminated. Moreover, because no work is required of this shaft 26, except to move the indicator dials, it is free from torsional deflection and the indication of measurement, therefore, is exceptionally accurate. In the mechanisms above described the relative approaching and receding movements of the grinding wheel and the work are produced by movements of the wheel or the wheel-head. It is obvious, however, that this same result might be produced by moving the work holder. Also, that in producing these movements of the wheel-head either the nut 26 or the screw [8 can be revolved while the other member remains stationary. It has here been considered more conven ent to revolve the nut. Both of the modifications just described are equivalents of the constructions shown and that the claims are intended to be interpreted accordingly.

While we have herein shown and described preferred embodiments of our invention, it will be evident that the invention is susceptible of embodiment in other forms without departing from the spirit or scope thereof.

Having thus described our invention, what we desire to claim as new is:

1. A grinding machine including a work holding device, a grinding wheel, a wheel head in which said wheel is mounted for rotation, and means supporting said wheel head and the work holding device for relative approaching and receding movements; mechanism for producing said movements comprising a screw-threaded shaft, a nut threaded on said shaft, said nut and said shaft being so associated with said wheel head and with said supporting means that rotation of the nut moves the wheel head toward and from the work, a motor, a speed reduction mechanism through which power is transmitted from said motor to said nut to revolve it, and an indicator driven by said speed reduction mechanism and constantly showing measurements of said relative approachin and receding movements.

2. In a grinding machine according to preceding claim 1, a construction in which said nut is in the form of a worm wheel, and said speed reducing mechanism includes a worm meshing with said nut to revolve it.

3. In a grinding machine according to preceding claim 1, a construction in which said indicator is mounted on and moves with, the wheel head,

and said screw-threaded shaft connects said wheel head with said supporting means on which the wheel head is mounted.

4. In a grinding machine according to preceding claim 1, a construction in which said indicatin mechanism is driven by the element of said speed reduction mechanism which engages and revolves said nut.

5. In a grinding machine according to preceding claim 1, a construction in which said speedreducing mechanism comprises a worm located substantially at the slow speed end of the speed reduction mechanism, and the driving element for said indicator is connected with said worm to be revolved in unison with it.

6. In a grinding machine including a grinding wheel, a Wheel head in which said wheel is mounted for rotation, devices for supporting the work for the operation thereon of said grindin wheel, and means supporting said wheel head and said work supporting devices for relative approaching and receding movements; mechanism for producing said movements comprising a screw-threaded shaft, a nut threaded on said shaft, said nut and said shaft being so associated with said wheel head and with said supporting means that rotation of the nut moves the wheel head toward and from the work, a drive shaft, a speed reduction mechanism connecting said drive shaft with said nut to revolve the latter, and an indicator driven from the low speed end of said speed reduction mechanism and calibrated to show constantly measurements of said relative approaching and receding movements.

'7. In a grinding machine according to preceding claim 6, a construction in which said indicator is mounted on the wheel head for movement toward and from the work with said head, and comprises a large dial positioned at a considerable elevation above the body portion of the wheel head.

8. In a grinding machine according to preceding claim 6, a construction in which said indicator comprises a vertical shaft connected with the lowest speed shaft of said speed reduction mechanism to be driven by the latter, a graduated dial on the upper end of said shaft, and a casing substantially enclosing said shaft and said dial.

9. In a grinding machine according to preceding claim 6, a construction in which said indicator comprises a vertical shaft connected with the lowest speed shaft of said speed reduction mechanism to be driven by the latter shaft, a graduated dial on the upper end of said shaft, a second graduated dial mounted to revolve around the axis of said shaft, gear connections between said shaft and the second dial for driving the latter in a predetermined speed ratio to the former, and a casing substantially enclosing said indicating mechanism.

10. In a grinding machin according to preceding claim 1, a construction in which said motor is of the variable speed reversible direct current type, whereby the variation in the rate of adjustment of the said relative approaching and receding movements can be produced by adjustment of the motor speed.

11. In a grinding machine according to preceding claim 1, a construction in which said motor is of the variable speed direct current type, whereby the adjustment of speed of the nut is obtainable directly by adjustment of the motor speed, and controlling apparatus for said motor, positioned remotely from it, but so connected with it and so organized as to control the starting,

stopping, reversing and the change of speed of the motor.

12. In a grinding machine according to preceding claim 1, a construction in which said speed reduction mechanism includes a changeable speed gearing.

13. In a grinding machine including a grinding wheel, a wheel head in which said wheel is mounted for rotation, and means supporting said wheel head and the work for relative approaching and receding movements; mechanism for producing said movements comprising a screwthreaded shaft, a nut threaded on said shaft, said nut and said shaft being so associated with said wheel head and with said supporting means that rotation of the nut. moves the wheel head toward and from the work, a motor, mechanism through which power is transmitted from said motor to said-nut to revolve it, and an indicator driven by the latter mechanism ,and constantly showing ,measurements vofsaid relative approaching and receding movements.

14. In a grinding machine according to preceding claim 6, a construction in which said indi" cator comprises-a vertical shaft connected with the-lowest speed-shaft of said speed reduction mechanism to be driven by the latter, and a of; the. nut moves; the wheel head toward and m h w rk, a m or, :6 D QdIQ QUiQILmW ',n sm. t roushswh ch powe is ,transmittedefr 'asaid, m r toisaid nuttmrevolre it, and an indicator driven by said speed reduction mechanism ,and constantly showing,measurementgofsaid approaching and receding movements.

17. In aerindin rmachine 1udinaa-gr n i e wheel, a; wheel head in which isaid; awheel is i mounted for rotation, and means supporting said r; wheel hea andhe :WDlk for rela ive: pproachins and. reced movemen s; mech nism for graduated dial mounted on the upper end of said vertical shaft and driven by said lowest speed shaft.

15. In a grinding machine including a-grinding mounted for rotation, means supporting said wheel head and the work for relative approaching and receding movements; mechanism for producing said movements comprising a screwthreaded shaft, arnut threaded on said shaft, said nut and said shaft being so associated with said wheel head and with said supporting means that rotation of the nut moves the wheel head toward and from the work, a variable speed reversible electric motor, mechanism-through which .power is transmitted fromsaid motor to-said nut to revolve it, and control apparatus for said motor comprising switches operable to start, stop and reverse it, the motor being equipped with anautomatic brake for stopping it instantly when the power supply to, it is cut oil, and'said controlling apparatus including an electronic rectifier system and means operatively connected, with it and adjustable to vary the voltage impressed on said motor so that'the speed ofrelative approaching and receding movements of,the wheel head-may .be adjusted by varying said-voltage.

16. A grinding machine of the class described, including a work holdingdevice, a 'wheel head, a grinding ,wheel mounted for rotation in the wheel head, said grinding wheel being adjustable in the wheel head toward andaway from the work holding device, means supporting said wheeLhead and 1, the work holding device for relative approaching and receding movements, in combination .with

mechanism for producingisaid approaching 1 and receding movements independently; ofadjustment of the grinding'wheel in the:whee1 head, said mechanism comprising a screwrthreaded-sshaft, a nut threaded on said shaft said-nut andsaid wheel, a wheel vhead in which said wheel is p odu ng; said mQYB G L SJ-CO HD iSing; a: screwthreadedshaft, anutgthreaded onsaid shait,;said

nut and saidgshaft being so associated ,Withsaid wheelhead :and with saidsupporting means-that I rotation of the nutmoves the wheel head toward H and from theework a motor, mechanism through which power is transmitted-from said; motor to said nut to revolve it, apparatus-remote fromsaid motor :but connectemwith it and organized to control the, operation ofqsaid motor, saidqmotor 3 being of the constant speed; type and said power transmitting meohanism,;in cluding changeable speed gearing; comprising a;- clutch operable to shift iromone speed ,toanothenswitches, remote from said motor ,butgconnected with it-to conshaft being so associated with said wheel head and with said work holding devic that rotation trol its operation, ,and electromagneticimeans for operating said clutch connectedwithpneof said switches tobe operated thereby.

HARRY ARTER. .tJWARREN F-EBASER.

, BEFERENCES, :CITED The following references are of record in the file of this patent:

UNI STA E P TENTS OTHER' REFERENCES Ser. No. 420,313, Fouquet A. P, ;C-;),;,:;pub1ished June 15, 1943.

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