US1623113A - Apparatus for and method of truing abrasive screws - Google Patents

Description

Aprilv 5 1927.

B. M. W. HANSON APPARATUS FOR AND METHOD OF TRUING ABRSIVE SCREWS Filed Nov. 5o, 192s 4 Sheets-Sheet 1 l! |llllllllllllllllllH d A llllllllll dlll Illlllllllllll'IIIIIIIIIIIIIIIIII Apll l 5 1927 B, M. w. HANsoN APPARATUS FOR AND METHOD OF TRUING ABRASIVE SCREWS Filed Nov. 30. 1923 4 Sheets-Sheet 2 ,4f l @Hoz 1112,11

A ril 5 1927.

p B. M. w; HANsoN APPARATUS FOR AND METHOD 0F TRUING ABRASIVE SCREWS Filed Nov. 50, 1923 4 Sheets-Sheet 5 April 5, 1927. 1,623,113

B. M. W. HANSON APPARATUS FOR AND METHOD. OF TRUING ABRASIVE SCREWS Fled Nov. 30. 1923 4 Sheets-Sheet 4 l no Patented Apr. 5, 1927.

UNITED' STATES PATENT OFFICE.

BENGT M. W. HANSON, OF HARTFORD', CONNECTICUT; EINAR A. HANSON AND CLAIR.-I ENCE E. WHITNEY EXECUTORS OF SAID BENGT M. W. HA'NSON, DECEASED.

APPARATUS FOR AND METHOD OF TRUING ABRASIVE SCBEB.v

Application led November 1923. Seria1.No. 677,632.

In' my co-pending application Serial No.l 675,034, filed November 16th, 1923, I have shown and described a machine for grinding gears, wherein an abrasive screw ot' emery or the like, and having a helical thread on its periphery, is employed for grinding the teeth of gears in a continuous operation, the machine being so arranged and constructed that the abrasive screw and gear blank are 1H driven at proper relative speeds with the thread of the abrasive screw meshingA with `the teeth onv the blank. The present invention is designed for triling, with precision, the'tlii'ead on the abrasive screw so that it l5 .will very accurately generate the desired form of tooth on a gear blank, for instance. By the use\of my improved invention, the abrasive screw, when it has become Worn, may be very expediently and' accurately dressed to the desired shape. y In the accompanying drawings, I have chown, forillustrative purposes, one vgeneral form of apparatus which I may employ in carrying out my invention, but it is to be understood that this showing is by way of eX- cmpliticatio'n only and is not to be construed as a limitation of the scope of the invention. Quite obviously, the machine and the methods carried out by the use thereof are susl) ceptible of various modifications, foi-ins yand changes.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereinafter Eiet forth, and the scope of the application of which will be indicated in the appended claims.

In said drawings:

Figure lis a front View of the machine;

Fig. 2 is a view looking at the left hand end thereof;

Fig. 3 is a view taken substantially on line 3-3 of Fig. 1 and looking in the direction of Ll l) '45 the arrows Fig. 4 is a top plan view of the gearing mechanism;

Fig. v5 is a top plan View, on an enlarged scale, ot the truing mechanism; and

Fig. 6 is a view` similar to Fig. 5 but showing another embodiment of truing device.

Referring to the drawings in detail, a denotes a base or iixed bed of any suitable a, for rocking movement about an axis construction on which is mounted a slide b provided with a bearing e for a spindle d carrying the abrasive screw c` to be ldressed or retrued. Pivotally mounted o'n the bifl pre erably parallel to that of the spingle d, is a rocking bed f on which is supported, for

sliding movement longitudinally of the abrasive screw e, a tool carriage g carrying a truing device l1.. .The rocking bed f is provided at its lefthand end with a rearwardly extending arm z' on which ismounted a gear box c housing the driving mechanism through which the rocking bed is rocked on.

its fulcrum and the tool carriage g is longi- .tudinally'reciprocated. The truing or resurfacing toolv is hereshown, by Way of example, in theforni of a diamond m, vand this tool is intermittently fed transversely of the abrasive scrcw through suitable mechanism Z controlled by the longitudinal reciprocat-` ing movement of the tool carriage g'. From the brief foregoing description, it will be understood that during the operation of dressing orKretruing the spiral rib or thread on the abrasive screw e, the diamond is vrepeatedly reciprocated longitudinally of the abrasive screw in accordance with the lead of the thread thereon, and the diamond is fed towards the abrasive screw each time the same is reciprocated so as to operate upon successive portions of the side facesl of the thread of the screw. In order that` the diamond -m will clear the abrasive screw on its return or inoperative stroke, the rock-y ing bed f is rocked, as hereinafter described more in detail. v In the present illustrative. disclosure of the invention, the work slide Z) is mounted on ways 1()4 on the upper face of the bed a. These ways are at right angles to the axis about which the rocking bed swin s. This slide may be adjusted in any suita le manner, as by means of a screw 11 (see Fig. 2) which may be turned by a hand wheel 12 on the forward end of a shaft 13, there being provided intermeshing gears 14 on this shaft and the screw. The spindle d', on which the abrasive screw to be retrued Ais mounted, may be driven in any suitable manner, as by means of a belt (not shown) passing about a pulley 15 fixed to this spin-dle.

The rocking bed is supported for' rocking movement in any suitable manner. By way of example, the rocking bed, may be journalled, as shown in Fig. 1, by means of ball bearings 20 on a shaft 21 supported for rotary movement by ball bearings 22 located in suitable brackets 24 arisin T from the front corners of the bed a. It wild be understood that there will be ball bearing arrangements 20 and 22 at each end of the bed f. The shaft 21, as hereinafter described in detail, is driven from theabrasive screw spindle d in order to reciprocate the tool carriage g and rock the bed f in proper timed relation to the rotary movement of the abrasive screw. The tool carriage g comprises a main slide 25 mounted on ways 26 for reciprocating movement on a line in'parallelisrn with the axis on which the rocking bed is fulcrumed, and a supplemental slide 27 on the upper face of which is fixed a plate or platform 28 for supporting the truing device h. The tool carriage g is reciprocated by means of a lead screw 29 which is intermittently driven in opposite directions in proper timed relation with the rotary movement of the abrasive screw e. The supplemental slide 27 may be adjusted on the main one 25 by means of avscrew 30 in order to properly adjust the diamond longitudinally of the abrasive screw.

The truing mechanism, as will be seen most clearly from Figs. 2 and 5, includes a table 35 mounted for angular adjustment in a horizontal plane upon the plate 28, and a holder 36 mounted on the table 35 for movement transversely of the abrasive screw, and, in the present case, at right angles to the axis about which the table is angularly ,adjustable) The plate 28 has, at its rear end, a boss 37 (see Fig. 2) forming a bearing which receives a stud or pivot pin 38 depending from the forward end of the table 35.' On the lower, end of this stud is screwed a nut 39 so as to hold the forward end of the truing device down. For the purpose of guiding and steadying the table 35, it may -be provided on its under face with an arcuate rib 40 working in an arcuate slot 41, the

center of curvature of which coincides with the axis of the pin or stud 38. The forward edge of the lplate 28 is curved, as shown in Fig. 5, and the table 35 is provided with a gib 42 (see Figs. 1 and 2) which receives this edge. The forward edge of the plate 28 is notched, as at 43, so as to receive a plunger 44 carried by the table 35. These notches will be of such number and so arranged that the tool holder 36 may be indexed to such angular positions that, when this holder is fed step bystep towards the screw, the dia# mond will be moved at an angle corresponding to the angularity of the side faces of the thread on the abrasive screw. In the present instance, two such notches are shown, these notches being so located as to permit the diamond to be moved to true the -a screw or bolt 65.

thread on the abrasive screw, the faces of which are at the usual pressure angle, namely 141/2".

The holder 36, together with the diamond carried thereby, may be intermittently moved in a direction transversely to the abrasive screw in any suitable manner, as by means of a .screw 45 threaded in the holder 36 andent instance, a ratchet wheel 47 is fixed to.

the screw 45, and journalled on the screw is a lever, on one arm 48 of which is pivoted a pawl 49 cooperating with the ratchet wheel 47 The other arm ,50 of this lever fis connected by a ball and socket joint'51 to a rod 52 slidably adjustable in a block 53 connected by a ball and socket joint 54 to the upstanding leg or arm 55 of a lever 56 pivoted, as at 57, to a plate 58 secured to and movable with the main slide 25 of the tool carriage g. Connected to another arm 59 of the lever 56 is a follower pin 60 which is guided, for vertical movement, in a bearing 61 provided on the lower end of the plate 58. The lower end of this follower pin rides upon a guide member or cam 63 which is in the form of a plate pivoted, as at 64, for angular adjustment, and adapted to be locked in any desired angular position by The lever 56 is normally urged in a clockwise direction, in order to maintain the follower pin 60--in engagement with the cam 63, by a spring pressed plunger 66 carried by the bracket 58 and engaging another arm 67 on the lever 56.

It will be observed that, owing to the ball and socket joints 51 and 54, and, due to the fact that the rod' 52 is longitudinally adjustable ina block 53, provision is made for permitting angular adjustment of the truing mechanism. It may be assumed that, when the tool carriage g moves towards the right, referring to Fig. 1, the diamond m is moved on its operative stroke, that is, it is operating upon the abrasive screw. During this operative stroke, the lever, which carries the pawl' 49, will be moved in a counterclockwise direction, andthe lever 56 will be urged in a clockwise direction to maintain the follower pin 60 in engagement with the guide member 63. When the tool carriage has reached the end of its operative stroke, the rocking bed f will be swung on its fulcrum so as to withdraw the diamond m from the abrasive screw, and then the tool carriage will be moved to the left, thatis on its inoperative stroke, and when so moved. the follower pin 60 will ride up the cam 63, thereby'lmoving the lever 56l counterclockwise, and rotating `the arm 48, which carries the pawl 49, in a clockwise direction. When this pawl is thus (rotated, it will turn the ratchet wheel 47, together with the screw on whichthis wheel is xed, a predetermined amount to feed the holder 36 and diamond point carried thereby forwardly a very slight distance;

As stated, it is advisable that on the return or inoperative stroke of the dressing tool m, it shall befree of the work. To this end, the rocking bed may be rocked in timed relation -with the longitudinal reciprocating movement of the tool carriage. In the present illustrative disclosure, this is accomplished by means of a cam fixed upon a shaft 76 journalled in the gear box which is mounted on the rearwardly extending arm z' of the rocking bed. Pivoted 'in abracket 77 fixed on the rear end of the arm i is 'a rocking beam 78, the long end or arm of whi rests upon the cam 75 and the other or s orter end or arm of which rests upon a pin 79 slidably carried by the bracket 77 and resting upon a suitable v abutment 80 on the fixed bed a. The cam 75 is Aintermittently rotated through 180.

It will beobserved that upon one-half revolution of this cam, the forward end of theA p rocking beam 78 will be lowered, permittin the rocking bed to swing rearwardly n n downwardlyl to bring the diamond point into operative relation to the abrasive screw.

On the, next half revolution of the cam, which occurs after the diamond point has made its operative stroke, the forward end of the beam 78 is raised, thereby swin ing the rocking bed in a direction to with raw the4 diamond point from operative relation to the abrasive screw so that the diamond point will be clear of the abrasive screw on the return stroke of the former.

The various mechanisms may be driven in any suitable or desiredmanner, but, by way of illustratioinl have shown one form of drive mechanism which may be adopted to advantage. The shaft 21 'is driven from the abrasive screw spindle d through 'a worin fixed on this spindle, a worm wheel 86 ont-he shaft 87, and bevel ygears 88 between the shaft 87 and the shaft 21. The

. upper end. of the shaft 87 is carried by a bearing or housing 89 suitably journalled on the spindle d, and one of the bevel gears 88 is s lined on the shaft 87 so as to permit of rociing movement 'ofthe rocking bed f and transverse adjustment of the slide b and the parts carried thereby. Within the gear box c is a shaft 90' which is constantly p driven from the shaft 21 through the gears .91. Fixed on the shaft 90'is a gear 92 (see Fig. 4) meshing with a gear 93 on the sleevel .94 which is'normally loose on the shaft 76 which carries 'the reversing cam 75. Fixed screw is the right to the shaft 76 is a cam sleeve 95 which con-4 trols the reversing' clutch mechanism for the lead screw through which the tool carriage g is reciprocated.

Between the sleeve 94 and the cam sleeve 95 is an escapement ratchet clutch mech` anism through which the shaft 76 is inter-- mittently rotated. In the prsent illustrative disclosure, this mechanism includes a ratchet wheel 100 fixe-d to the sleeve 94 and a pawl 101 as at 102, to a disk 103 fixed to the sleeve 95. The pawl 101 is urged into engagement with the ratchet wheel by a spring pressed plunger 104 carried by thedisk 103. ivoted upon a bracket 105 fixed tothe gear box c are a air of pivoted levers 106 the inner ends o which are diametrically disposed relative to the ratchet wheel 100, as shown most clearly by dotted lines in Fig. 2. .The outer ends of these escapement levers are, y means of spring pressed plungers 107, maintained against opposed abutments 108 upon a vertlcally movable rod 109 connected at its lower end to a lever 110 fixed on a shaft 111 which extends forwardly to the front of the machine. On theforward-end of this shaft is fixed an arm 112 (see Fig. 1) connected by a link 113 to a lever 114 pivoted to the rocking bed. The link 113 may be connected to the lever 114, as shown in Fig. 1, when the abrasive provided with a right hand thread, for instance. If an abrasive screw with a left handv thread is to be retrued, in which case it may be presumed the tool carriage should bemoved towards the left on its operative stroke, the link 113 would be con. nected to the left hand arm 114 of the lever 114. Connected to this lever 114 is a rod 115carrying adjustable dogs 116with which to cooperate. f

It will be observed that, when the tool carriage reaches the end of its operative stroke, in the present instance, its movement. Itowards the right, referring to Fig. 1, the dog 117 on the tool carriage will strike the right hand dog 116 thereby moving the rod 115 to and, through the connections described, rotating the shaft 111 in a direction to lower the rod 109. When this rod is thus lowered, theupper escapement lever 106 is swung in a direction to release the pawl 101, whereupon this pawl will engage the ratchet wheel 100 causing the shaft 776 and the cam 75 carried thereby to rotate. Rotation of this shaft, however, is limited to the shaft has made one-half revolution,the pawl 101 strikes the lower escapment lever 106, whereupon this pawl is disengaged from `the ratchet wheel 100. When the tool carfor, after (see"Figs. 2 and 4) pivoted,

carriage.

115 to the left and, through the connections described, the rod 107 will be raised, whereupon the lever escapementl lever 106 will be released from the pawl 101, 'permitting the same to engage the ratchet wheel 100. The

shaft 76'will now be rotated another half revolution and then' the upper escapement lever 106 will disengage the pawl 101 from the ratchet wheel.

The lead screw 29, by means of which the tool carriage is reciprocated, is driven from the shaft 90 in the following manner. Located adjacent the shaft 90 is a shaft 120 and between this latter shaft and the lead Screw are a train of gears 121. These gears are adapted to be changed so that the tool carriage may be moved in accordance with the selected pitch of the thread on the abrasive screw. Fixed on the shaft 90 are a pair of gears 122, 123. The gear 122 is in meshnwith a gear 124 loose on the shaft 120. The other gear 123 drives, through an intermediate gear 125 Xed on a stub shaft 126, a gear 127 also loose on the shaft 120.` It will be seen that the gears 124 and 127 vare constantly driven 1n opposite directions. The clutch mechanism. for alternately {ixin the gears 124 and 127 to the shaft 120 may ifhe of any suitable construction. In the present instance, this clutch mechanism includes a sleeve 1284having at each end a single clutch tooth 129. The gears 124, 127 ,are respectively provided With a-single clutch tooth 124 and 127 adapted to cooperate with corresponding clutch teeth 129 on opposite ends of the sleeve 128. These parts are provided with single clutch teeth-to insure uniformity in the reciprocating movement of the tool The clutch mechanisnrjust described is controlled by the ratchet clutch mechanism which, in turn, is controlled, as heretofore stated, by thelreciprocating movement of the tool carria e. The sleeve 95 has a cam groove 130 in w lich works a pin 131 carried by a shipper lever 132 suitably pivoted on a stud 133. The groove 130has an offset 130 'to permit the lever 132 to be thrown into neutral misitiqn, as by means of a handle 140 on the upper end of the stud 133. Journalled'on this stud is an arm 134 having, in its free end, a -pin 135 which works in a groove 136 in the clutch sleeve 128. One end of the shipper lever 132 is provided with a pair .of arms between which is positioned a web or rib 137 on the arm 134. The arms of the shipper lever 132 carry4 spring pressed plungers 138which respectively engage opposite sides of the rib 137. The arm 134 is provided in order to prevent iamming of the parts in the event that,

when the shipper lever is thrown, a tooth on the clutch sleeve 128 should strike the top of a tooth on one of the gears 124, 127.

The operation of the mechanism is briefly as follows; When the abrasive screw\ has become worn to such an extent that it should be retrued, it is secured to the spindle d. With the reversing cam 75 in such position that the rocking beam rests upon the lowest point of'this cam, the slide b will be adjusted to move the abrasive screw laterallyy into operative relation to the diamond point; the truing device will be properly indexed upon the plate 28 in accordance with the angularity of one of the side faces of the thread on the abrasive screw; the supplemental slide 27 of the tool carriage will be adjusted by the screw 30 so as to bring thediamond point into proper relation longitudinally of the thread on the abrasive screw, and the holder 36 will be manually advanced or adjusted by turning the screw to engage the diamond point with the face of the thread,

preferably, at a `point at the outside edge of this face. Assuming that the operative parts of the machine have been properly lselected and set up, the Ymachine may be thrown into operation by turning the handle 140 to proper position. The lead screw will now move the tool carriage on its operative stroke during which the diamond point will take a cut on one face of the thread throughout its length. After the tool carriage isA moved to the right to such extent that the diamond point is beyond they abrasive screw, the dog- 117 on the tool carriage will strike the right hand dog 116 onthe rod 115 whereupon, through the mechanism described, the reversng cam 75 will be rotated 180 to swing the rockin bed upwardly and forwardly and there y withdraw the diamond point from operative position and'then the lead screw will be' reversed to -move the tool carriage on its inoperative stroke. During this inoperative stroke, the cam'or guide member 63 will raise the follower or pin 60 and thereby cause the ratchet mechanism associated with the screw 45 to turn this screw a very slight amount and thereby feed the diamond point one step towards the abrasive screw. When.the work carriage has completed its inoperative stroke, the cam 75 will again be rotated 180o whereupon the rocking bed will swing rearwardly and downwardly to bring the diamond point into operative position with respect to the abrasive screw, and then the work holder will again be moved on its operative stroke, during which time the diamond point will take another cut in the face of the thread just inwardly of the previous cut. This sequence of operations is repeated until one face of v the thread is retrued throughout its depth.

Then the truing device is angularly adjusted or indexed so that the diamond point will operate upon the other side face of the screw. The outside or truncated face of the thread on the abrasive screw may be trued by very slowly moving, by means of the screw 30, the diamond `point in a straight line in In Fig, 6, I have shown, more or less diagrammatically, an arrangement of truing mechanism which may be employed to advantage'when it is desired to true an abrasive lscrew having a thread with its side faces other than straight in the direction of their' depth. In this ligure, I have shown the abrasive screw as having a thread with 'double curve faces so that the abrasive screw, in outline, will correspond to a double curve yrack'adapted to mesh with the double curve gear to be ground. Referring to this ligure, 27 designates the supplemental slide of a tool carriage; 28, the plate thereon; 35 a table; and 36, a tQol or diamond point holder. In the present instance, the tool holder 36 may be moved in a direction laterally-of the abrasive screw in the same manner as in the preceding embodiment. The screw 45 has a nut 150 slidable in a groove 151 in the bottom of the holder 36 so as to permit this holder to move laterally of itself under thel inuence of cams 152. These cams, which constitute pattern means, have their operative faces corresponding in all particu ars to the shape to be given to the side faces -of the thread on the abrasive screw. The holder 36 is provided with projections 153 which engage and follow the curved faces of the cams 152. The holder- 36 is urged in a direction to maintain the projections 153 in engagement with the cams 152 in any suitable manner, as by means of spring pressed plungers 154 carried by the table-35. y.It will be understood that,

with the .arrangement just described, the dia- A mond point, a ter each operative stroke 1ongitudinally of the abrasive screw, will be fed slightly inwardly towards the axis of this screw by turning the screw 45", and when the diamond point is thus fed inwardly, it will move slightly longitudinally of the abrasive screw, owing to the cams or patterns 152. When one face of the thread on the abrasive screw has been trued up in the manner justtdescribed, the pattern cams 152 are reversed and inverted so that the cam surfaces thereon will take the dotted line positions shown in this ligure. The other. face of the thread on the abrasive screw may then be retrued. The cams 152 are .diagrammatically shown as being held in position by suitable screws 156 and lugs 157.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope-thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a Sense.

I claim as my invention: ,i 1. In combination, means for rotatably supporting an abrasive screw, a tool for truing therthread on said screw, and means for repeatedly and relatively moving said tool and abrasive screw longitudinally of the axis of the latter and in accordance with the lead of the thread thereon with said tool engaginga side face of said thread at successive points in th'e direction of its depth.

2. In combination, means for rotatably supporting an abrasive screw, and diamond point for truing the thread on said screw movable longitudinally of. saidscrew in accordance with the lead of the thread thereon and intermittently movable laterally of the screwin accordance with the shape of the faces of said thread. I

`3. In combination, means for rotatably supporting an abrasive screw, a tool for truing the thread of said screw, means for repeatedly moving said tool longitudinally otthe abrasive screw in accordance with the lead of the thread thereon, and means for intermittently moving said tool laterally of the screw in accordance with the angularity of the side faces of the thread thereof.

4. In combination, means for rotatably supporting an abrasive screw, a diamond for truing the thread of said screw, means for repeatedly moving said diamond longitudinally of the abrasive screw in accordance with the lead of the thread thereon, and automatically actuated means for moving said diamond with a step by step movement along the faces of the thread in the direction of their depths.

y5. In combination, means for rotatably supporting an abrasive screw, a tool for truing the thread of said screw, means for reciprocating said tool longitudinally of said screw in accordance with the lead of' the thread thereon, means yfor feeding the tool axially of said screw in accordance with the shape of the side faces thereof upon each reciprocating movement of said tool, and

supporting an abrasive screw, a tool for truing the thread on said screw, means operatively connected to said spindle for reciprocating said tool longitudinally of the abrasive screw in accordance with the lead Qf the thread thereon, means controlled by the reciprocating movement of said tool for intermittently feeding said tool along the face of the thread in the direction of its depth, and means operatively connected to said spindle for withdrawing said tool from the abrasive screw upon the return movement of said tool.

8. In combination, means for rotatably supporting an abrasive screw, a ,diamond polnt for truing the thread on said screw mounted for angular. adjustment correspoiding to the angles of the faces of the thread on said screw and movable longitudinally of said screw in accordance with the lead of the thread thereon and laterally of said screw in accordance with the angles of the side faces of the thread thereon. r

9. In combination, means .for rotatably supporting an abrasive screw, a diamond point for truing the thread on said screw, a holder for said diamond point mounted for angular adjustment whereby the same may be moved at an angle corresponding to the angle of the side faces of the thread on said abrasive screw, means for reciprocating said holder to move said diamond point longitudinally of the screw in accordance with t e lead of the thread thereon, and means for feeding said holder in its angular positions of adjustment laterally of the abrasive screw.

10. VIn combination, means for rotatably supporting an abrasive screw, a tool carriage mounted for rocking movement about an axls parallel to the axls of said screw, means for reciprocatmg said tool carriage longitudinally of the scibw in accordance with the lead of the thread thereon, a tool on said tool carriage, means intermittently feeding said tool on said carriage laterally of the abrasive screw in accordance with the shape of the faces of the thread, and means actuated in timed relation to said reciprocating means for rocking said tool carriage to withdraw'th'e tool from the abrasive screw on the inoperative stroke of the tool.

11. In combination, means yfor rotatably supporting an abrasive screw, a'rocking bed arranged to swing about an axis parallel to the axis of the screw, a tool carriage mount- -ed on said bed for reciprocating movement axially of said screw, a tool holder mounted on said carriage for intermittent feedlng movement transversely ofthe abrasive screw,

and a cam driven in timed relation to the reciprocatin movement of said carriage for rocking sai bed to withdraw the tool 'from the abrasive screw upon the reverse stroke of said tool carriage.

12. In combination, a spindle for rotatably supporting an abrasive screw, a rocking bed mounted for` swinlging movement about an axis parallel to t e axis of said screw, a tool carriage mounted for movenient on said .rocking b ed axially of said screw, a tool holder mounted on said tool carriage for angular adjustment/in accordance with the angularity of the ofaces of the thread on said screw, a lead screw connected to said spindle for reciprocating said tool carriage in accordance with the lead of the thread on said screw, a cam driven in timed relation with said lead screw for rocking said bed to withdraw the tool on the reverse stroke of said tool carriage, and means controlled by the reciprocating movement of 'said carriage for feeding said tool holder ,laterally of said screw.

13. In combination, means for rotatably supporting an abrasive screw, a tool for truing the thread on said screw, means for reciprocating said tool axially ofthe screw in accordance with t e lead of the thread' the contour of the side face of the thread in the direction of its depth.

15. In combination, means for rotatably supporting an abrasive screw, a tool for truing the thread on said screw, means for reciprocating said tool longitudinally of said screw in accordance with the lead of the thread thereon, means for moving said tool laterally of said screw with a step by step movement, and pattern means for guiding said .tool when it ist so moved laterally in conformity to the contour of the side faces of the thread on said screw.

16. The method of truing a thread on an abrasive screw which consists in taking helical cuts in a side face of the thread at successive points in the direction of its depth.

17. The method of truing a thread on an abrasive screw `which consists in rotating the screw and repeatedly moving a tool longitudinally of the axis of the screw'in accordance with the lead of the thread thereon with said tool engaging a side face of said thread at successive points in the direction of its depth.

18. The method of truing a thread on an abrasive screw which consists in rotating the screw, repeatedly reciprocating a resurfacin tool axially of the screw in accordance with the lead of the thread thereon, and moving the tool laterally of the screw with a step movement upon each reciprocating movement in accordance with the -shape of the side faces of the thread on the screw,

.BENGT M, W. HANSON,

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