US2188947A - Grinding or abrading machine - Google Patents

Description

Feb. 6, 1940.

GRINDING Filed July 9, 193

S. A. HORSTMANN 0R ABRADING MACHINE l0 Sheets-Sheet 1 133 INVENTOE Swine: Adolph Horsimann ATT'L Feb. 6, 1940.

S. A. HORSTMANN GRINDING on ABRADING MACHINE Filed Jul 9, 1938 10 Sheets-Sheet 2 s. A. HORSTMANN 2,188,947

GRINDING OR ABRADING MACHINE I Fiied July 9, 193a 10 Sheets-Sheet s Feb. 6, 1940.

EY/ II/ arl/l \NVE NTOK Swine Adolph Horsi'mqhn.

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'I IIIIIIIIIIIIIIIIIII Feb. 6, 1940. s. A. HORSTMANN GRINDING OR ABRADING MACHINE 'Filed July 9, 1938 10 Sheets-Sheet 4 v INVENTO? Sidne Adolph flnrsl'mqnn- Feb. 6, 1940.

S. A. HORSTMANN GRINDING 0R ABRADING MACHINE Filed July 9, 1938 10 Sheets-Sheet 5 N YE NTOCQ.

W L I; ATTY' Feb. 1940- I s. A. HORSTMANN 2,188,947

'GRINDING 0R ABRADING MACHINE Filed July 9, 1958 10 Sheets-Sheet 6 I/ I 1y M V 9 20% id! w/ W I I my {9.9

Sam 5 Add k Hovsl'mq an Feb. 6, 1940.

s. A. HORSTMANN 2,188,947

GRINDING on ABRADING momma Filed July 9, 1938 10 Sheets-Sheet 8 N VENTOIE.

Feb. 6, 1940.

s. A. HORSTMA'NN GRINDING 0R ABRADING MACHINE Filed July 9, 1938 10 Sheets-Sheet 9 15/ 214 o o u o 0. Q

Qd n 2 Ad Mph orflmum @Q W MA H.

Feb. 6, 1940. s. A. HORSTMANN 8,

GRINDING 0R ABRADING MACHINE I Filed July 9, 1938 v 10 Sheets-Sheet 10 6., GIRWML I R H.

Patented Feb. 6, i940 2 1 3 947 UNITED STATES PATENTV'OFYFICE Application July 9, 1938, Serial No. 218,285

In Great Britain July 10, 1937 14 Claims. (Cl. 51-95) This invention relates to improvements inas above described it is possible to employ a grinding machines such as are used, for example, reversible liquid motor and to provide a valve to produce screw threads on gauges, taps and for reversing the flow of liquid to the motor, other threaded articles by means of the action of th reby reversing the direction of rotation of r, a suitably formed grinding wheel on the Work the work piece. Such an arrangement is'quite piece; The chief object of the present invensatisfactory but it is a further object of the tion is to provide a generally improved and simpresent invention to provide an improved method plified thread grinding machine in which all backof reversing the direction of rotation of the Work lash is avoided and in which the work head caread Wh W l ave e ad t t t rying the work piece to be ground is rotated reversal can be effected Without in any Way altero in a very simple and efficient manner. n the sett ng of the liqu d ot a ly dr v- Now-it will be readily appreciated that in the ing the Work head. production of screw threads by grinding it is According to this feature of the present inne-cessary to provide means whereby the speed vention, a separate motor is provided for re- 15' at which the work head of the machine is driven versin'g' the work 'piece, this additional motor 15 may be varied from time to time, for example, and also theliquid motor normally driving the to suit the various diameters of the work being Work head bein adapted o drive e d S GW produced. Heretofore such speed variation has through a common differential gear, the cage been obtained by the use of variable speed elec- Of w h s Op V y Connected t e d tric motors, variable speed belt drives and/or screw. a

changes of gearing. All such means are not only The liquid motor" which is employed to drive cumbersome and to a certain extent inefficient the lead screw in the forward direction drives but, in addition, they serve only the individual one of the side wheels of the differential gear function in question and do not readily adapt in one direction whilst the separate reversing themselves to the simplified carrying out of the motor (which may-conveniently be an electric other functions of the machine. It is, therefore, motor and is hereinafter termed the .electric an object of the present invention to provide motor) is adapted to rotate the other side wheel simple and efficient means of driving the work of the differential gear in the opposite direction.

head of a grinding machine at the desired speed, Normally the electric motor is switched off, in

which means also lend themselves readily to the Whichcase the lead screw is rotated in the for- 30 carrying out of certain other desirable or even ward direction fromthe cage but, when itis necessary operations of the machine. desired to reverse the travel of the work piece, According to the principal feature of the presthe electric motor is-switched on to rotate its ent invention, a liquid motor, preferably ofthe side wheel of the differential gear at a speed rotary type, is employed to drive the work head, greater than that at which the other side wheel 35 said liquid motor being supplied with liquidunis driven and'in the reverse direction; The reder pressure from a liquid supply such as a pump sult is that the cage, and hence the lead screw, which is appropriately driven from the main drive is driven in'the reverse direction at a speed which of the machine or by means of a separate drive is dependent upon the difference in speed of 40 as desired. the two side wheels of the difierential gear. As 40 One or more suitable valves is or are provided the speed at which the'electric motor drives its to control the amount of liquid supplied to the side of the differential gear may be quite high liquid motor and hence to control the rate at without any ill effects (sincea out is not taken which the work piece is rotated. on this traverse) it follows that the'work piece 5 i In a thread grinding machine since it is inmay be quickly returned-to its initial position advisable to disengage the lead screw nut from ready for the" next" out provided the grinding the lead screw when traversing the work piece Wheel and the work piece have been separated back, it is most desirable to provide means whereprior to the electric motor coming into operaby the direction of rotation of the work head tion. Furthermore; since the reversal is depend- 0 and consequently the axial movement of the cut only on the difference of speed ofthe two 504d work piece may be reversed in order to bring motors, it will be obvious thatthe liquid motor the work piece back to its initial position after may be left running in the normal way during it has been traversed across the edge of the the reversal and thatas soon asth-eelectric mogrinding'wheel. v tor is switched o'ffi'the liquid motor will imme- With a liquid motor drive to the work head diately take over the drive-and will advance the work piece at the predetermined speed. All need of re-setting the liquid motor after each reversal is thereby rendered unnecessary and, furthermore, it is unnecessary that the liquid motor should be of a type which is capable of being reversed.

It is convenient to include in the circuit of the electric'motor a make and break switch which is only closed when the grinding wheelhas been fully retracted from the operative position. By this means all chance of the work piece being reversed whilst still in engagement with the grinding wheel will'be avoided.

The electric motormay be started and stopped by means of a manually operable switch or by means of appropriate make and break switches adapted to be operated by pre-set stops carried by the work head or any other suitable part at,

the ends of the traverse.

The liquid employed for the liquid motor is preferably oil and, according to a further feature of the present invention the oil pressure obtained from the pump driving the liquid motor is also used to; operate the work slide and to keep a constant pressure against the lead screw.

According to a still further feature of the present invention, this oil pressure is employed notv only to damp the grinding wheel slide but also to cause operation of the same as hereinafter described.

This oil damping of the parts not only eifectively prevents backlash but also provides adequate lubrication of the parts.

Several other novel and advantageous features are provided by the present invention, these being fully described hereinafter and claimed in the appended claims.

In order that this invention may be-the more clearly understood and readily carried into effect, I will proceed to describe the same with reference to the accompanying drawings, which illustrate by way of example and not of limitation one convenient embodiment of the present invention, and in which: I

Figure l is a front elevation of the complete machine, and l Figure 2 is an end elevation of the same;

Figure 3 is a plan View of the machine.

Figure 4 is a front elevation on an enlarged scale of the lead screw and head stock' portion of the machine, and v Figure 5 is a section on line 5-5 of Figure 4.

Figure 6 is a central vertical section through the lead screw andgear box assembly, and

Figure 7 is a central vertical section through the gear box.

Figure 8 is a section on line 8-8 of Figure 6 illustrating the construction of the sine-bar compensator.

Figure 9 is an end elevation of the head stock.

, Figure 10 is a part sectionalv plan view of the preferred form of reversing gear for reversing the direction of rotation of the work piece at the end of its traverse across the grinding wheel.

Figure 11 is a section on line ll--H of Figure 10 showing the electric motor drive to the differential gear, and

Figure 12 is a section on line l2-l2 of Figure l0 showing the liquid motor drive to the differential gear.

Figure 13 is a front elevation of the tail stock device. Figure 14 is a plan view of the same, and Figure 15 is a section online' l5-l5 of Figure 13.1 1..

Figure 16 is a part sectional view showing the grinding wheel shaft arrangement.

Figure 17 is an end elevation of the grinding wheel quadrant and torque reaction assembly.

Figure 18 is a central vertical section through the grinding wheel slide bar assembly.

Figure 19 is a View showing the mounting of grinding wheel housing.

Figure 20 is a front elevation of the mechanism for setting the grinding wheel for different helix angles, and I Figure 21 is a plan View of this mechanism.

Figure 22 is a view similar to Figure 20 showing the grinding wheel set for a widely diiierent helix angle.

Figure 23 is a somewhat diagrammatic front elevation of part of the machine showing oneform of automatic stop and reverse mechanism in one position, and

Figure 24 is a similar view showing the said mechanism in its other position.

Figure 25 is a section through the preferred form of hydraulic reverse valve for controlling the movement of the grinding wheel slide, and

Figure 26 is a similar view showing the plunger of the valve in the other position.

Figure 27 is a front elevation of the head stock 7 illustrating a device for relieving taps, and.

. Figure 28 is a somewhat diagrammatic plarr View illustrating the setting of the machine for grinding taper threads.

I Figure 29 is a diagram illustrating the fluid sys- I tern of the machine, and

Figure 30 shows the circuit of the electric connections.

Referring now to the drawings and more particularly to Figures lto 3 thereof, the'thread grindingmachine comprises a base we on top of which is mounted a bed lfil, the base and bed being of substantial thickness and weightto avoid any vibration whilst themachine is running. In

order still further to isolate the bed it from any vibrations which may be transmitted thereto from the base Iiiil, rubber'or otherresilient pads may be inserted between the bed and thebase so that Y i there is no metal to metal contact between the.

parts. On one side of the base vlflilis mounted the electric motor I02 which is adapted to drive a I fluid pump m3 mounted .on the opposite side, of the base. ply the fluid; preferablyrlubricating oil, under pressure for the operation of the, machine. order to maintain a constant oil pressure the pump M3 is provided with a suitable bye-pass valve 5 83a, (Figure 29)- which may be incorporated This fluid pump m3 is adapted to supin. the casing of the pump and which is adapted when necessary to bye-pass the oil backto the main supply tank )4. Oil under, pressure is-lfed from the pump ms tothe rotary-fluid motor I05 which is used to drive the lead screw and to rotate the work piece as will now be described.

Lead screw and -work piece rotating means (Figures 4 to 9) v The slide on which the headstockand tail stock are mounted comprises a circular steel .or other suitable bar W6 which extends from side to side of'the bed ml. At the right hand end, as shown in thedrawings the slide bar I06 passes through a large bearing I88 firmly fixed to the bed I ii into a casing Hit which houses the leadscrew 0.

'l'he-leadscrew Ill] projects; into'the slide bar taken up. The lead screw lever and nut II I is rigidly fixed to the sine-bar lever part III by means of screws II5 whilst the sine-bar lever is also attached to the slide bar I06 by means of the screws I I6 which, as shown in Figure 8, are capable of the necessary slight movement.

The head stock III is clamped to the slide bar I06v at the desired part by means of the clamp H8 and is provided with an outstanding lug II9 which extends out over the edge of the bed I M and is flanked on either side by ears I which serve the purpose of causing a small bearing plate I2I on the edge of the bed to follow the movement of the head stock. The bearing plate I2I has upstanding pins I22 located be- I pre-set, this screw I22a engaging with the bearing plate I2I. This adjusting and setting screw is particularly useful when the machine is to be used for tap relieving, as hereinafter described.

The head stock is provided with two housings I23 and I24 respectively, said housings being parallel with one another as shown in Figure 5 and spaced apart horizontally. The inner housing I23 rotatably carries a sleeve I25 in the forward end of which is fixed the head centre I26. sleeve I25 at its forward end also carries .a pinion I 21 and the usual outstanding arm I28 for rotating the Work piece.

The other housing I24 also rotatably houses a sleeve I29, to the forward end of which is fixed a pinion I30 gearing with the pinion I21 on the sleeve I25. The rotatable sleeve I29 is, however, splined on a driving shaft I3I so that it is free to slide axially along the same.

The driving shaft I3I is connected by a spherical seating joint I32 to a driving clutch sleeve I33 (the use of the clutches will be described hereinafter) which is provided with a sprocket wheel I 34 which is adapted to be driven by a chain I35 from the fluid motor I05 through the special form of reversing gearing according to the present invention, which will hereinafter be described.

At its remote end the sleeve I33 is connected by means of a spherical seating joint I36 to a short shaft I31 which extends into the gear box I38.

The sleeve I33 is thus supported between the shafts I 31 and I3I, and it will be appreciated that the spherical joints I32 and I36 will ensure an adequate drive whilst compensating for any lack of alignment of the parts.

Inside the gear box I38 the shaft I31 is provided with a gear wheel I39 which is adapted to drive through the intermediary of the gear train I4I, a gear wheel I42 which is fixed to the end of the lead screw I I0 where it projects into the gear casing I38. The gear train MI and also the gear wheels I39 and I42, if desired, are interchangeable in order that the speed at which the lead screw III] is rotated may be varied for the purpose of cutting threads of different pitch. For use in cutting left-hand threads an idler gear (not shown) may be interposed between the I gears I39 and MI.

It will thus be seen that when the sprocketwheel I34 is driven the work piece will be rotated through the sleeve I33 and shaft I3I whilst the lead screw 0 will be rotated through the gearing and will cause the slide bar I06, carrying with it the head stock and work piece, to be traversed across the machine.

The sprocket I34 is driven by the fluid motor I05 so that by controlling the amount of fluid supplied to the motor the rate of rotation of thework piece and also the rate of traverse of the work piece in the machine will be simply and effectively varied.

The casing I09 in which the lead screw is disposed may, if desired, be partly filled with oil so that adequate lurbication of the lead screw H0 is secured.

Now it will be appreciated that it is often required to pick up a thread on an existing threaded piece or to reduce the effective diameter of a thread being produced. For this purpose it is, of course, necessary that the work piece should be very accurately positioned relative to the grooves on the grinding wheel. With thread grinding machines as heretofore constructed this has been a matter of some considerable difficulty but with the lead screw arrangement according to the present invention it may be very easily effected. The means for securing this adjustment comprise a micrometer screw I43 controlled by the handle I44 and screwing into the end bearing I45 for the lead screw H0 in the gear box I38. The end of this screw I43 engages with a ball I46 which, in turn, engages with the end of the lead screw. It will be seen that by turning the handle I44 the whole lead screw, slide bar and head stock assembly may be moved bodily in the machine and the position of the work piece accurately adjusted relative to the grinding wheel so that a thread may be picked up.

Sine-bar compensator A sine-bar compensator for accurate adjustment of the pitch of the thread being cut is provided. Sine-bar compensators have been pro vided in thread grinding machines as heretofore constructed but the lead screw arrangements according to the present invention lend themselves readily to the provision of a simple and very effective construction of sine-bar compensator. This device is provided inside the casing I09 which is provided with a slot or opening I48 covered by a cover plate I49. Pivoted at its centre to the underside of this cover plate as at I50 is the sine-bar I5I which is of channel section and is provided towards its end with adjusting screws I52 passing through the side of the cover plate. By adjustment of these screws the sinebar may be adjusted. The arcuate slots I53 in the cover plate co-operate with pins 400 to indicate the setting of the sine-bar. The lever I l I carrying the lead screw nut is provided with an extension I54 carrying a ball I55 which lies in the sine-bar I5I.. It will be seen that by adjustment of the sine-bar and co-operation of the same with the ball I55 the work piece may be arranged to lead or lag slightly on the actual pitch of the lead screw H0.-

Hydraulic damping of the lead screw It was mentioned above that the use of a fluid motor which is driven by oil or the like under pressure was advantageous iii/connection with:

other operations and functions of the machine.

One such additional use to which the oil' under;

pressure may be put is the hydraulic damping of the lead screw and the work head slide and the prevention of backlash therein. It is for this purpose that the cylinder I01 above mentioned is employed. Oil under pressureis conveyed from the pump through the pipe I56 and admitted to the cylinder I01 through the port I51 so as to maintain a constant oil pressure therein. The work slide bar I slides in and out of this cylinder as the work is traversed and acts as a piston. At all times, however, the work slide bar I06 will be subjected axially in one direction to the pressure of the oil in the cylinder and this pressure will be transmitted through the slide bar I to the lead screw H9 and lever r I H to take up any backlash therein. The lead slight leakage of oil from the cylinder I01 will adequately lubricate the slide bar I05 at this bearing and will keep the same free from grinding dust and metal swarf.

Reversing gear (Figures 10' to 12) The desirability of providing reversing gear for the lead screw drive so that the work piece can be returned to its original position after a out has been taken Without the necessity of disengaging the lead screw nut from the lead screw has been mentioned above. One way of doing this would be to use as the fluid motor I05 a reversible motor and to provide a valve by means of which the flow of fluid under pressure to the motor I05 is reversed. Whilst such an arrangement is, from. some aspects, quite satisfactory (and it must be clearly understood that I do not exclude such an arrangement from the present invention but wish to cover the same), yet it has certain disadvantages. For example, such an arrangement essentiallyinvolves an alteration of the setting of the fluid control valve H950; (Fig. ure 29) and the re-setting of the same to its original position after the reverse has been effected. It is preferred, therefore, to use the reversing gear shown in Figures 10 to 12 of the accompanying drawings which overcomes these isadvantages. This arrangement employs a separate electric motor I58 in addition to the fluid motor I05 for the purpose of reversing the work piece.

The chain I which drives the sprocket I34 passes around a sprocket I carried by the cage I60 of a dilferential gear I51. One side wheel I02 of this differential gear is driven through a worm gear I33 from the fluid motor I05 whilst the other side wheel I64 of the differential gear is driven also through a worm gear I from the electric motor I58, the fluid motor I05 and the electric motor I58 being suitably supported with their shafts parallel toone another on an extension of the bed IOI. An adjustable end bearing I60 may be provided to prevent any end play in the spindle of the electric motor which would tend to prevent the smooth running of the worm gear I05.

During the cutting operation the side wheel I64 of the differential gear is stationary and so the cage I60 rotates at one half the speed of the other-side wheel I62 ofthe differential gear and drives the sprocket I34. through the chain I35'. The speedhatawhicht the wheel I62 of the.

be left unaltered: if desired. This side wheel Hi2.

of the difierential gear rotates continuously at; the same: speed whilstthe machine is operating.

.When it is desired t'o-reverse the work piece,

the grinding wheel is first retracted from the work piece in the manner hereinafter described andthen the electric motor I58 is switchedon" to rotate the side wheel I64. of the diflerential gear at. a higher speed than the wheel I62 and in the opposite direction. The electric motor 158 uses thecontinuously rotating side wheel-I62 as a reaction, and it will be seen that the cage ital and hence the sprocket I34 will be drivenin the reverse direction, the speed being one-half the diiference in speed of the two side wheels I62 and I54. As the electric motor I58 may be set to rotate the side wheel I04 at a comparatively high speed without any ill-efiectssince a cutie not taken on the reverse traverse, the. work piece may be quickly returned to its original position without unnecessary loss of time.

Immediately the electric motor I58 is switched 011 the liquid motor I05 will take up the drive again through its side wheel I52 to advance the work piece at the predetermined speed.

It is convenient to include in the circuit of the electric motor 153 a make and break switch which is only closed when the grinding wheel has been fully retracted from the operative position; One suitable arrangement and operation of such switch will be described hereinafter, and it will be seen that by this means all chance of the work piece being reversed whilst still in engagement with the grinding wheel will be avoided.

Tail stock and. centre (Figures 13 to 15) with a bearing plate I15 slidably arranged on the bed I01 of the machine, the bearing plate being provided with pins I15 which engage with the ears 113 and cause the bearing plate to follow the movement of the tail stock.

Slidably mounted in the tail stock I10 is a plunger I11 which carries at its forward end the tail stock centre I18 and which at its other end extends. into an hydraulic cylinder I19 which is mounted on the tail stock. Oil under pressure is fed to the cylinder I19 from. the pump I03. through the pipe I80. The plunger I11 acts as a piston in the cylinder "I19 and the constantv pressure of the oil in the cylinder I19 will ensurev a constant loading of the tail stock which is very desirable. A two-way cock I8I- is included in the pipe I00 so that when desired the pressure can be shut off from the cylinder I19 and the fluid already in thecylinder emptied through the outflow pipe I82. A compression spring I83 is also I provided within the cylinder I19 bearing on the plunger H1 so that the work piece is lightly held even when the hydraulic system is not in operation Not only does this hydraulic actuation ensure a constant pressure on the tail stockcentre andfigive steadiness of operation but, in"- addition, the slight leak from the cylinder 'I 19 around the plunger I11 will give adequate'lubrication of the rod and will keep the rod free from grinding dust and metal swarf.

Hand operation of the tail stock for theflpurpose of inserting and removing the workis provided by means of the hand lever I84 which is pivoted in a bracket I85 on the cylinder I19 and has a rod I86 which extends through the end of the cylinder. Internally of the cylinder the rod I86 is provided with a head I81 engaging in a groove I88 in the plunger I 11. 'It will be seen that by means of the lever I84 the tail stock may be retracted when desired.

Grinding wheel mounting may be admitted through the port I93. It will thus be seen that when oil under pressure is admitted to the cylinder I99 and not to the cylinder I92 the grinding wheel slide bar I89 and the parts carried thereby will be moved forwardly in the machine and that when oil under pressure is admitted to the cylinder I92 and not to the cylinder I 99 the slide bar I89 will be similarly moved rearwardly. I

An adjustable stop screw I94 is passed through the end of the rear-hydraulic cylinder I99 to limit the backward movement whilst the cylinder I92 at the front of the machine is provided with a micrometer adjusting screw I95 operated by the handle I96 and provided with a scale ring I91 so that a very accurate adjustment of the forward position of the slide bar I89 .is obtained. On the forward movement of the slide bar the grinding wheel is engaged with the work piece so that by adjusting the screw I95 any. desired depth of cut may be obtained. The force keeping thegrinding wheel in engagement with the work piece is, it will be seen, the pressure in the cylinder I99 and as this is the constant pressure supplied by the pump. I93 the grinding wheel will alway's'engage with the work piece at a constant pressure. Furthermore, the slight leakage of oil from the cylinders will provide adequate lubrication of the slide bar as in the case of the work slide bar I96; Clamped to the slide bar I89 is the grinding wheel housing bracket I98 on which the grinding wheel and its associated parts are all mounted. To this end the bracket I98 is provided at its upperend with a substantial bearing rI99'which is adapted to receive'an extension 299 outstanding from the back of the housing 29I for the grinding wheel'292. The extension 299 is apush fit in the bearing I99 and the arrangement is such that the axis of the bearing I99 passes through the centre of the grinding wheel 292.

The grinding wheel 292 is driven by a shaft 293 mounted in bearings 294 in a' sleeve 295 which is clamped in an outer tube 395 which, in 'turn,'is' bolted to the grinding wheel housing 29L The advantage'of mounting the grinding whee'l'292 and sleeve 295 in the outer tube 395 is that the position of the grinding wheel may be adjusted to the desired relation to the axis of the bearing the sleeve 395.

I99 w'hatever be its width. The shaft 2931s driven by anelectric motor 264 by the belt drive 265, the pulleys 296 being adjustable in order that the speed at which the grinding wheel is rotated may be varied.

The electric motor 264 is mounted at one point only at each end on rubber bushes carried in brackets 291 carried by the tube 395 and the grinding wheel housing, and a rubber or springloaded torque reaction rod 298.. is connnected from a bracket 299 on the front of the sleeve housing or tube to a point near the top of the motor 264 in order to steady the same. This gives a floating suspension for the motor drive.

It will be seen that the whole of the grinding wheel assembly and the electric motor is carried in the. bearing I99 and this arrangement is very advantageous for setting the grinding wheel for different helix angles. For this purpose there is. provided at the back of the machine a shaft 2I9 having at its outer end an operating handle 2| I and at its inner end a worm 2I2 driving a pinion 2I3 which is carried by a shaft 2I4 extending-forwardly of the machine in a bearing 2I5. At its inner end the shaft 2I4 is provided with an arm 2I6 having an outstanding pin 2". The pin 2i 1 is located in a slot 2I8 in an arcuate scale plate 2I9 bolted or otherwise secured to It will be seen that by operation of the shaft 2I9 the scale plate 2I9 may be raised or lowered thus causing the whole grinding wheel assembly to swing in the bearing I99. By this means an accurate setting of the grinding wheel 292 for the desired helix angle is obtained. 'Once the grinding wheel has been set the extension 299 is clamped in thebearing I99 and the scale plate 2I9 is clamped in position by means ofthe bolt 29I.' Of course, any other means of rocking the grinding wheel assembly for the purpose of setting the helix angle may be employed without departing from the scope of the present invention.

It has been pointed out above that it is desirable to include a make-and-break switch in the circuit of the electric motor I58 driving the reversing gear so that the said motor can only be switched on after the grinding wheel 292 has been fully retracted from the work piece. The movement of the grinding wheelhousing bracket I98 or of the slide bar I89 may be employed for this purpose in any suitable way. For example, a contact rod may be provided on the end of the slide bar I89,.this rod passing out through the hydraulic cylinder I99 and being adapted to (bridge a pair of contacts when the grinding wheel hasbeen fully retracted. Alternatively, the grinding wheel quadrant I98 may be linked to a switch in such a manner that the switch is only switched on when the grinding wheel has reached its fully withdrawn position. I

For forming or dressing the grinding wheel it is preferred to use the method described in my copending British patent application No. 5212/37, according to, which a preformed dressing roller with a helical thread is mounted in the work piece position and'pressed against the grinding wheel, the two parts being rotated at the same, or substantially the same, peripheral speed. In carrying out this method with the presentmachine it is convenient to switch off the electric motor 264 and to screw a removable handle 229 into one of the pulleys 296 so that when the forming roller has been pressed into engagement with the grinding wheel the same may be rotated at a slow speed by hand.

:of the accompanyingdrawings and comprises a hand lever 22! pivoted at 222 on the bed .of the machine and extending below the pivot where it is attached to the plunger of a hydraulic reversing valve. This hydraulic reversing valve, the construction of which is shown in Figures 25 and 26, is employed to control the admission of oil under pressure to and its release from the hydraulic cylinders I50 and I92. It will beremembered that in controlling the movement of the grinding wheel assembly it is necessary to admit oil under pressure alternatively to thehydraulic cylinders I and I92 to allow any oil in that cylinder to which oil is not being fed to be released. This operation is effected by the hydraulic reversing valve which comprises a valve body 223 suitably mounted on the bed of themachine. Slidably mounted in the central bore of this valve body is the plunger 224 which at its forward end is connected to the hand lever 22I and which is provided with two spaced peripheral recessees 225 and 226. Oil under pres-. sure from the pump is fed-through a pipe 221 to the inlet port 228 of the valve body and spaced on eitherside of the inlet port 228 are two outlet ports 229 and 230. The outlet port 229 is connected to the front hydraulic cylinder I92 whilst the outlet port "235 is connected to the rear hydraulic cylinder I90.

Also bored in the valve body is an outlet passage 23! which is connected by a pipe 232 to the oil reservoir, this passage communicating with two ports 235 and 234 spaced as shownand opening on to the central bore of the valve body.

When the plunger 224 is in the position shown in Figure 26 oil under pressure will flow from the inlet port 228 round the recess 226'and out of the port 230 so that it will be fed to the rear hydraulic cylinder. At the same time'the port 229 connected with the front hydraulic cylinder will be placed in communication with the outlet passage 23l through the port 233 and the recess 225 and so any oil in'the front hydraulic cylinder can'exhaust. The grinding wheel will, therefore, be brought into engagement with the work piece. When'the plunger 224 is moved to its other position shown in Figure 25 the-operation will be reversed. The rear hydraulic cylinder will be allowed to exhaust through the port'23ll, the recess 225, port'234 and passage 23I whilst oil '.under pressure will be supplied to the front hydraulic cylinder I92 through the inlet port 2'28, peripheral recess 225 and the port 229. The grinding wheel will thereupon be retired from the work piece. Thus it is merely necessary tomove the handle 22I from one position to the other in order to control the grinding wheel.

This change-over operation may, if desired, be effected automatically at theends of the traverse of the work piece. For this purpose a bar-235 may be pivoted to the hand lever 221, this bar extending along the front of the bed of the machine and passing through a slide or eye 236 fixed to the bearing ,plate I2I associated with the head stock. Mounted onv the bar .235, .one each side of theeye 236, are two-adjustable stops 23! which are set to correspond to the desired travel of the. work piece. Since the eye 236 is constrained to follow the. movement of the head stock it will engage with the stops 23:! just prior to the end of its traverse and in .sodoing will operate the hydraulic reversing valve.

the present invention.

-iIt: :will.1.-be readily zappreciate.d"' that? it .is gdesirable that-the plunger :shall be. maintained firmly dead-centre device, is provided according to The bar 235 instead of being merely pivoted on the pin 500 carried "by the hand lever '22I is;provided with an elongated slot 50I where itpasses about the pin 500; The

:hand lever ;22I is thus capable of a certain amount of -movement in one direction or the other relative to"the=bar. 235. :Mounted on the pivot 222 of the hand lever 22I is a bell crank lever 552, one arm of which extends upwards to the pin 500 and the other arm5il3 extends outwardly'from the side of'the lever 22! and'is provided with a pointed nose 5%.

being pivoted as at 5E3! on thevvalve casing223. A tension spring v568 is connected between the coursethe right-hand end of the slot 5!" in'the bar- 235 engages-with the pin :500 and commences toswing-thehand lever in ananti-clockwise direction. In doing so it causes the upper surface of'thenose 504 to ride up the under suriaceof the nose 1506 thereby separating the-lever 22 i and the arm 5135 andincreasing-the tension on the spring. This movement continues until the pointsof'the noses meet whereupon the spring '5Il8'fcomes into play to snap the lever over sharply untilthe pin 500 :engages with the left-hand end of theelongatedslot 501 and this ensures the rapid change-over of the-valve plunger 2 24.

The under surface of the nose 504 now engages with the upper surface of the nose 505 as shown in "Figure 24 and the spring 508 holds the valve in'itsrnewiposition. In passing fromtheposition,

shown in Figure .24 to the position shown in Fig- .urei23, the reverse action takesplace as will be readily appreciated.

With

'Co-operating v with the nose 504 is an arm "595 which is also provided with a pointed nose "585,-the arm 505 In due n If desired, the bar 235 maybe connected to 7 one arm of :a pivotal bell crank'lever .238, the other armor which is connected to a switch 239. This switch is connected in thezcircuit of thereversing gear electric motor and'is only switched on when'the reversing valveis set to retire the grinding wheel. Similarly, when'thereversing valve is setito the other positionto advancefthe grinding wheel up to the work piece, the switch 239 .will be switched oif and this will form. an additional safeguard to prevent the worlr piece being reversed whilst in engagement with the grinding wheel.

It-will be appreciated :that the automatic op- I eration of the :reversingvalve need not be car-- ried out by direct mechanical action -from'the movement of the head stock as above described. For example, the head stock or any part associated with it may be adapted to close a pair of electric contactsat each end of its traverse, these contacts being included in the circuits. of solenoids adapted to operate the valve plunger 224 to :move' the same backwards and forwards as required. Alternatively, one of the solenoids may bereplaced .by a spring or any-other meansfor securing the automatic operation of the reversing valve may obviously be employed without departing from the scopeof the present invention; 'piston,"means for supplying liquid under. pressure Furthermore, the change-over valve may,' if desired, be mounted inside the machine.

Tap relief means The machine according to the present invention also lends itself readily to the relieving of taps as they are being ground. The tap relieving mechanism comprises a ring 240 secured tothef shaft I3I of the lead screw mechanism so as to rotate therewith, said ring being provided with holes 24I into which are appropriately inserted pins 242 to correspond with the particular tap being ground. Outstanding from the right hand ear I20 of the head stock. is a pin 243 on which is the pins will engage withthe arm 244 andwill cause the same to rock about the ball 245; Hence since the pin 243 on'which the arm 244 ispivoted to the head stock is on the remote side of the ball 245 the whole head stock will be twisted to give the desired effect. The us'ejof the circular slide bar I06 permits the head stock to move readily since'it merely turns in its bearings. The setting screw I22 limits the return movement of the head stock andensures that it will always return to the correct position. The amount ofv relief of the tap may obviously be-varled by adjusting the adjusting screw 246.

The machine according to the present invention is furthermore readily adaptable to the grinding of taper threads since, as shown in Figure 28, it is merely necessary to twist the tail stock on the circular slide bar I06 in order to secure any desired taper.

The fluid system of the machine according to the present invention is shown in Figure 29, like references being used to indicate like parts, and

Figure 30 shows the electric circuit arrangements; 250 is the switch operated by movement of the grinding wheel quadrant.

The features of the present invention may, if desired, be incorporated in an internal thread grinding machine, suitable modifications being effected in the grinding head and work holders.

Any of the known forms of coolant maybe employed, the same being provided from an outside pump or by a pump on the machine as desired.

Although, the present invention is more particularly intended for use in thread grinding machines, it will be obvious that it is equally applicable to the production of screw thread milling. cutters and other like articles which are formed with annular grooves.

I claim:

1. In a thread grinding machine, a work-head for supporting the work piece, a slide bar carrying said work-head, a liquid motor actuating said work-head, and hydraulic means acting upon said slide-bar to unilaterally bias the same, whereby back-lashis prevented.

2. In a thread grinding machine, a work-head for supporting the work piece, a slide bar carrying said work-head, a liquid motor actuating said work-head, supporting means for said slide bar, said supportingmeans including'a cylinder into which said slide-bar extends, the portion of the slide-bar extending into said cylinder forming a from said'motor to said cylinder to act upon said 3.-The deviceclaimed in claim 1, including a lead-screw, means connecting'the latter to the said slide-bar, whereby the said biasing pressure is transmitted to the saidlead-screw. 4. A thread grinding machine as claimed in claim 1, comprising a .lead "screw, a separate f 'r'notonfladifferential gear connected therewith,

said'gear being alsoconnected to said liquid motor and including a cage, the latter being'connected 'to the lead-screw, said separate motor being capable of a speed different from that of 6. A 'thread grinding" machine according to claim 2, in which the work-head slide bar is of circular cross-section and said Work-head comprises a head-stock, the same being adjustably mounted on the said circular slide bar, means being provided for locating the radial position of the said slide bar relative to the bed of'the machine..

7. The device claimed in claim 1, including a piston, whereby said work-head is constantly v biased in one direction and back-lash prevented.

lead-screw, means connecting the latter to the said slide-bar, whereby the said biasing pressure is transmitted to the said lead-screw; said slide-bar having circular cross-section, and a lead screw nut carried by that end of the said slide bar remote from the hydraulic cylinder, said lead screw nut being engaged by the said lead screw, the latter extending into the slide whereby the fluid pressure is applied to the lead screw and nut to prevent back-lash between the same. '8. The device claimed in claim 1, including a lead-screw, means connecting the latter to the said slide-bar, whereby the-said biasing pressure is transmittedto the said lead-screw and a micrometer adjustment device operatively connected to the said lead screw to move the same and said slide bar carrying the head-stock bodilyin an axial direction.

9. A thread grinding machine according to claim 1, comprising a grinding wheel, a round bar slide for the'said grinding wheel and hydraulic means for axially biasing said bar slide. 10. A thread grinding machine according ,to claim 1, which comprises a grinding wheel, a motor for driving the same, said grinding wheel and the motor therefor forming a single assembly, a round bar slide, a single bearing and a quadrant supporting said assembly being mounted on the said round bar slide.

11. A thread grinding machine according; to claim 1, which comprises a grinding wheel, a mo-,

tor for driving the same, said grinding wheel and the motor therefor forming a single assembly, a

round ba'r slide, a single bearing and a quadrant l' :roundi bar slide; a single bearing and a. quadrant supporting said assembly being mounted on the saidsrou-nd bar slide, a pair of hydraulic cylinders,

to-the lead-screw, said separate motor beingcapable of a speed different from, that of said liquid motor, whereby due to the difierential gear the direction of movement of the Work piece is reversible; a circuit connection for said separate motor and a make-and-breakswitch disposed in the circuit of the electric motor, a grinding wheel, a bar slide supporting saidvgrinding wheel, means for actuating said-grinding wheel, said bar slidexfor the grinding wheel being operativelyz'connected to said. switchfthe latter being operatedb'y movement of the said grindingwheel 7 slide so that the 'switchis only closed after the grinding wheel has been retired from the work' piece wherebyall possibility of the Work piece be- I ing reversed whilst still'engaged by the grinding Wheel is avoided.

14. A thread grinding machine according tof ,claim 1, which comprises a grinding'wheel; a

motor for driving the same, said grindingwh'eel, and the motor therefor'forming a single as-,

sembly, a round bar slide, a single'bearing and a quadrant supporting said assembly being mounted on the said round bar slide, a pair of hydraulic cylinders, said round bar slide for the grinding wheel extending at each end into one v I of said hydraulic cy1inders,.fiuid under pressure being admitted to one or. the other of said cylin-' I ders not only to providea hydraulic bias on. the

slide but also to cause movement of the slide bar and the grinding wheel carried thereby, and;

means for'exhausting the fluid from-one hydrau- I r lic cylinder when fluid under pressure is admitted to the other. l I

I ADOLPH HORSTKVIANN

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