US3026549A - Lead screw means with half-nut engageable when in alignment with lead screw threads - Google Patents

Description

March 27, 1962 HARTSHORN 3,026,549

. 8. LEAD SCREW MEANS'WITH HALF-NUT ENGAGEABLE WHEN IN ALIGNMENT WITH LEAD SCREW THREADS Filed March 51, 1958 3 Sheets-Sheet 1 IN V EN TOR.

T 3 DERlCK $.HARTSHORN ATTOR/Vly 3,026,549 EN IN March 27, 1962 D. s. HARTSHORN LEAD SCREW MEANS WITH HALF-NUT ENGAGEABLE WH ALIGNMENT WITH LEAD SCREW THREADS 5 Sheets-Sheet 2 Filed March 31. 1958 IN VEN TOR. DERICK S. HARTSHORN BY W ATTORNEY March 1962 D s. HARTSHORN 3,026, 49

LEAD SCREW MEANS WITH HALF-NUT ENGAGEABLE WHEN IN ALIGNMENT WITH LEAD SCREW THREADS Filed March 31, 1958 3 Sheets-Sheet 5 I INVENTOR. DERICK S. HARTSHORN ATTOPAZY rates This invention relates to thread-chasing devices and, more particularly, has reference to an apparatus for forming threads in a rotating work piece, which apparatus will be of generally improved design as regards devices of this type previously conceived.

A more specific object is to provide a thread-chasing device having novel means for automatically initiating and terminating movement of the threading tool and of the threading tool support means, longitudinally of the work piece, whereby said device will be automatic in operation and will be operable to thread a plurality of like work pieces in following order, with a minimum of attention on the part of the machine attendant. While threading operations are being performed the machine attendant or machinist would usually remain watching the threading operation, as it is very rapid while using carbide tools and on short threads makes the cut in a matter of seconds. As the slide is snapped back at the completion of threading of a particular work piece, the operator would shut off the control circuit. If the operator fails to shut olf control, the tool will repeat its path and thereby consume time though making no further change in the work piece. It is thus proposed to carry out this object with minimum possibility of damage or affecting of the work, and it is further proposed that when used on a turret or engine lathe, threading operations performed by the device can be carried out as one of a series of operations carried out on the machine, so that the part would not need to be inserted in the machine for threading only.

Another object is to incorporate in the device a cross slide structure which will feed transversely of a main slide that moves longitudinally of the work piece, with the cross slide structure being advanced transversely to progressively greater depths into the thread groove formed in the work, during successively following passes of the main slide longitudinally of the work.

It is further proposed that when the device is used for a special or single purpose, such as a continuous run on an automatic machine, a cam type traverse would be used and in this event the feed cam would be so designed that it would need no manual setting.

A further object is to provide manually settable means, capable of being calibrated as desired, for presetting the cross slide structure in respect to the depth of the groove to be formed in the work, with the structure thereafter being self-feeding radially inwardly of the'work on successively following passes of the main slide.

Another object is to incorporate an electro-mechanical means for controlling the cycle of operation of the machine, unless a cam traverse is used.

In the instant invention, the device is made with the lead screw as the means for effecting traverse of the main slide. However, a model could be made with a cam traverse. The cam would'be so designed that the chasing tool would cover the same path at every stroke. Such a design may be entirely satisfactory for various applications of the invention. In other instances, a traverse of the type illustrated and described herein may be employed. Thus, the cam traverse design as embodied in an actual working model, has been found entirely satisfactory except for the following:

(1) With a cam giving a traverse of two-inches, much time is lost on short threads; and

(2) If different cams were used, the time of changing cams would be an objection as well as their cost. Multiple lobe cams would not involve changing of gears other than those required for different threads.

In this connection, a three inch cut is about the maximum practical and this has been found entirely satisfactory for most thread chasing operations. The lead screw arrangement illustrated and described herein permits one to change the length of the stroke readily, and all that is necessary is to change the location of a bridge which will also be described in detail, by adjusting the bridge position longitudinally of and along the ways of the base. In this way, the device illustrated and described herein can cut a thread approximately seven inches long.

Still another object is to provide a machine as described that will be particularly accurate in respect to the thread-chasing operations performed thereby, will be capable of manufacture at comparatively low cost considering the benefits to be obtained from its use, and.

will be rugged and substantially trouble-free in operation.

A further object is to include novel means including first and second cross slide members connected by a.

toggle linkage, in a manner such that at the completion of each pass made by the main slide longitudinally of the work, the bit will be automatically retracted, and will be subsequently fed into the work once again on the initiation of the next cycle of operation.

Still another object is to incorporate, in the cross slide structure referred to immediately above, means for pre positioning one of the slides, so as to provide, in elfect, an adjustably positioned base point from which the toggle linkage is extended, to locate the bit at a selected, ad-- justed depth relative to the work.

For further comprehension of the invention, and of the objects and advantages thereof, reference will be had to the following description and accompanying drawings, and to the appended claims in which the various novel features of the invention are more particularly set forth.

In the accompanying drawings forming a material part of this disclosure:

FIG. 1 is a top plan view of a thread-chasing apparatus according to the present invention, parts being broken away.

FIG. 2 is a side elevational view thereof, a portion of the adapter being broken away, shown in section.

FIG. 3 is a transverse sectional view on line 33 of FIG. 1.

FIG. 4 is a transverse sectional view on line 4-4 of:

FIG. 1.

FIG. 5 is a transverse sectional FIG. 1.

FIG. 6 is a transverse sectional View on line 6-6 of FIG. 1.

FIG. 7'is a sectional view through the thread-chasing bit holder, substantially on line 77 of FIG. 6.

FIG. 8 is a horizontal section, online 8-8 of FIG. 6.

view on line 55 of FIG. 9 is a wiring diagram showing the circuit of the other portions being.

stituting the present invention has to be positioned in reference to the work piece. Means for positioning the same would be on the larger machine, such as a lathe, to which the device is attached. If the device is incorporated in a larger machine, the machine would need a spindle, means for driving it at various speeds, gear changes for different threads, ways for longitudinal and transverse movements and a connection from the machine spindle to the lead screw of the thread chasing device constituting the present invention. When once positioned for the same type of work piece, the machine constituting the present invention remains fixed unless the larger machine on which it is mounted is also performing other operations on the same work, in which case the thread chasing attachment could quickly be positioned by means of stops or graduations on the moving parts.

Adapter 10, at its upper end, is connected rigidly to a flat base 12, said base being formed with a longitudinally extending, wide, dovetail tongue 14.

It would be understood that the device would be used largely as an attachment, and thus would be so designed as to fit different types of machines in most commercial embodiments of the device. Accordingly, it is for this reason that an adapter 10 is used. All attachments would be made to the base 12 of the device, or to the main slide or bridge described hereinafter, so that the only requirement for fastening the device to any type of machine would be the adapter, unless a cam traverse is used.

Machines of the same type and make would have different distances from the cross slide to the spindle center so that no adapter would fit more than one type and size of machine.

A bridge 16 extends transversely of the base, fully from side to side thereof, as clearly shown in FIG. 1, said bridge at one side projecting laterally outwardly of the base a short distance.

The bridge 16 has been shown to particular advantage in FIGS. 1, 3 and 4, and as shown in FIG. 4, is formed formed on its underside with a dovetail groove 18 receiving the tongue 14. The bridge 16 is thus bodily adjustable in a direction longitudinally of the base, to selected positions upon the base. In each position to which the bridge is adjusted, it may be fixedly secured on one side, as for example by screws 20 (see FIG. 4) threadedly engaged to bear against a gib. Even though the main slide and the cross slide may be of relatively light weight material such as aluminum, the weight thereof is such that when the parts are returning at high velocity, the impact must be absorbed largely by the screws 20 at the side of the bridge and hence, screws of substantial size are desirable. Other means might be employed, designed to obtain the same result of permitting adjustment of the bridge and fixed connection of the same to the base in a selected position of adjustment.

Secured to the bridge at one end thereof (see FIG. 3) is a switch 22, which can be, per se, completely conventional. Switch 22 can be a normally closed micro-switch or the equivalent, and has an outwardly spring-pressed movable switch contact 26 and an elongated arm 28 pivotally mounted at 27 on the housing of the switch in the path of movement of a device carried by the main slide.

Designated generally at 30 is a main slide, including a plate-like slide body 32, said main slide being formed, as shown in FIG. 6, with a dovetail groove 33 receiving base 12.

At the end of the main slide, adjacent bridge 16, there is integrally formed upon the main slide, medially between opposite sides thereof, an upwardly projecting, approximately semicircular, transversely extending lip 34 (FIGS. 1 and Adjacent one side of the lip, there is formed therein a threaded opening in which is engaged a screw 36 (FIG. 1), adapted to engage a movable lug or button 38 of a switch provided upon the bridge 16 to actuate the switch.

A belt 40 is extended through an opening 41 formed in the bottom edge of bridge 16 (FIG. 4), and is secured to the main slide at the location of lip 34. Belt 40 is trained about a vertically disposed pulley or roller 42 (see FIG. 2), rotating in a vertical plane in a longitudinal slot 44 formed in the base adjacent bridge 16 (FIG. 1). The pulley 42 has a stub axle 46 rotating in bearings 48 of a pulley bracket 49 fixedly secured to the base.

Belt 40 is extended downwardly from the pulley 42, and at its lower end is secured to the bifurcated end 23 of a vertically disposed bolt 43 that extends downwardly within a large opening of a vertically elongated weight 50 of oblong cross section. Bolted to the top surface of the weight 50 is a crossbar 45, that covers the upper end of the bore 47 of the weight.

The lower end of the bolt 43 is threaded, and threadedly engaged with the bolt and adjustable longitudinally thereof is a disc or washer 31, against which abuts a compression, coil spring 39. Spring 39 extends within bore 47, and at its upper end abuts against the crossbar 45. Bolt 43 is freely slidable in a center opening 35 of the crossbar.

Guide rods 37 are fixedly secured at their upper ends to the bracket 49, the guide rods being loosely positioned through guide openings 29 of the crossbar. The rods are threaded at their upper ends and carry adjusting nuts 37'.

As a result, when the main slide to which the belt is connected is shifted toward the right in FIG. 2, the weight is pulled upwardly, with the belt traveling upwardly and to the right in FIG. 2 about the pulley 42. Ultimately, the crossbar 45 will engage the nuts 37' preventing any further upward movement of the weight. As the traverse of the main slide continues in a direction toward the right in FIG. 2, the disc 31 will now begin to move upwardly with the bolt 43, Within bore 47 of the weight, and spring 33 will begin to compress more and more.

As a result, the pressure on the strap or band will be greater than that exerted by the weight ordinarily, so as to insure a proper return movement of the main slide and prevent excessive impact upon the bridge that would tend to otherwise loosen the bridge.

The weight is not heavy enough on short strokes to retract the mechanism. However, on long strokes it will carry the slide back with sufficient speed once it is started.

Adjustment of the spring pressure may be regulated for different conditions by changing the location of the nuts 37' to selected positions downwardly from the bracket, so that the location at which the weight is engaged against further upward movement can also be adjusted to initiate compression of the spring. A crossbar below the weight will pick it up on long strokes and take off the load if the velocity is too great.

A radial lug or block 52 is fastened to the belt 40 and carried around thereby.

Lug 38 constitutes a movable switch contact, it being understood that the switch associated with lug 38 may be engaged in a suitable recess provided in the bridge 16, said switch being somewhat diagrammatically represented at 53 in FIG. 1. Switch 53 is normally open, being closed by closing movement of the lug 38 by screw 36 carried by the main slide, when the main slide 30 is moved to the maximum extent to the left in FIG. 1, to its initial or starting position shown in this figure of the drawing.

In any event, a solenoid contactor or relay 54 is mounted upon the main slide, for a purpose to be made presently apparent. The contactor is simply an electrically operated device.

Threadedly engaged in the bridge 16 is a screw 56, having a reduced, elongated axial extension 58, the distal end of which is rounded off, said extension providing an adjustable stop for a toggle linkage to be described in detail hereinafter.

Adjacent the screw 56, bridge 16 carries a pivoted,

spa e 1o sleeve extension 6d at one side thereof, and (see FIG. 4) a knurled adjusting sleeve 62, formed with internal threads and rotatably engaged in a complementary recess 63 of extension 66, receives an elongated, threaded stem ea, thus to shift the stem 64 in an axial direction without rotation of the same, responsive to rotatable movement of the knob or sleeve 6'2.

At its free end, the stem 64 is formed with a sharpened tooth as (see FIG. 1), thus to provide a pawl.

The pawl is swingably mounted, since the sleeve 60 is pivoted on the bridge by means of the screw or pivot pin 68. in this connection, a spring means would be provided, in a commercial embodiment tending to hold the pawl 66 in engagement with the ratchet, so that the pawl will remain in contact with the ratchet wheel in any of various positions to which the ratchet wheel may be shifted transversely of the main slide during operation of the machine. The pawl 66 pushes the ratchet wheel around.

An auxiliary or cross slide assembly includes a cross slide base 70 which, as shown in FIG. 7, is of channeled formation, having a guideway 72.

it will be understood that the cross slide base could be pivoted on the main slide on the same center as the back pivot stud when the auxiliary slide is retracted. It might be positioned by screws extending into the main slide with the base at an angle of 90, 76 or 61 with the main slide as desired. This would allow cutting of a square thread, an acme thread, or a V thread respectively, although all threads might be cut at 90. Ninety degrees is the only angle at which a square thread can be cut and chasing is the only method used in cutting a square thread.

In the illustrated example, the cross slide base 7% is rigid with the main slide 32. It could be secured to the main slide, as for example, by bolts, and in fact, could be pivotally adjustable upon the main slide about a ventical axis perpendicular to the length of the cross slide. In the illustrated example the cross slide base is fixedly secured to the main slide in a position in which its length is inclined slightly out of perpendicularity to the length or path of movement of the main slide. The channel or slide base 7t} could be otherwise arranged, of course, andmight be exactly perpendicular to the length of the main slide, or at some angle of inclination other than that shown in FIG. 1.

in any event, at its opposite ends, the guide channel or trackway '72 is closed by end plates 74, 76 which extend transversely of the slide base 70 and are bolted in place, to the body of the slide base.

Forward. plate '74 serves to seat one end of a pair of compression springs that will be described hereinafter, there beingv slight recesses in the plate 74 for this purpose. The rear plate 76 takes the thrust of a cam to be hereinafter described, and as will be noted from FIG. 8, plate 76 has a notch into which the cam retracts in one position of the cam.

Slidably engaged in the channel 72 are first and second cross slides 78, 86, respectively (see FIG. 8). The cross slide 78 carries a bit support block 82 secured thereto by screws 86, said block 82 having a cover plate 84 (see FIG. 7 Smooth-walled, registering openings of cover plate 84 and block 82 are in registration with threaded, upwardly opening recesses of the slide 78, and accordingly, the cover plate can be engaged in place, cooperating with the body of the block 82 in clampably engaging a bit 33. Bit 38 is of any desired cross-sectional shape, and in the illustrated example is of rectangular section, with the cover plate and body having confronting, endto-end channels in which the bit is clamped. The bit is adapted to form threads in a work piece 90 which would besuitably held adjacent the device constituting the present invention, and which would be rotated simultaneously with the longitudinal advancement of the main slide along the tongue 12. Holding the bit securely in place are clamping-screws 92 threadedly engaged in. the,

cover plate.

The first or bit support slide 78 is movable outwardly as viewed in FIG. 1, and when it has reached the limit of.

its outward movement, that is, when the free or workengaging end of the bit is at the depth of the thread grooves formed in the work 9%, means is provided to re-- tract the slide 78. This includes a pair of compression springs 94, one end of which are seated in recesses 75 in plate 74 and the other end in recesses 96 in the cross slide.

Referring now to FIGS. 1 and 6, a pin 93 threadedly engages in the rear end of slide '78, and passes through an opening formed in one end of a toggle link 100, the other end of which is overlapped with and pivotally connected to a second toggle link 162 by means of a pin 104. Link 1% pivots on pin 98, and link 102, as shown in FIG. 6, has a pivotal connection to the slide 80, provided by a vertically elongated pin 1'66, threadedly engaged in slide and extending within a bushing 108 which is free to rotate on pin 1% and which is keyed at 110 to a hand knob 112, a ratchet wheel 114, and a cam 116. Link Hi2 and bushing 188 are relatively rotatable.

Stud or pin 1% (see FIG. 6) has adjacent its base portion a collar or shoulder W7, which reduces the thickness of the cam 116, and which spaces the cam away from the slide 30. This increases the strength of the stud at this location.

Slide 80 is only half the height of slide 78, or stated otherwise, is only half the depth of the groove 72. The remaininghalf of the depth of the groove is occupied by the cam 116 and shoulder 197 so that the top surface of the cam is flush with the top surface of the slide base '70. Links rec, 102 are in contact with said top surfaces of cam 116 and slide 78.

Referring to FIG. 8, earn 116 has a spiralling periphery, producing a pronounced step 113 where the portion of the periphery, that is, at the greatest distance radially from the axis of the cam meets that portion of the periphery which is at the smallest distance in the same direction. In other words, the feed is rapid at the start and gradually grows less and less rapid until at the last 15 the curve is concentric with the center of the cam rotation.

In FIG. 1 the toggle links are shown in longitudinal. alignment, that is, the toggle is straightened out. The links, however, are adapted to be angularly related, with. the connecting pin T04 of the toggle shifting in the direction of the arrow shown in FIG. 1, to the left in this figure of the drawing.

Limiting swinging movement of the toggle links me, 162 in respectively opposite directions are abutments mounted upon opposite sides of the channel 72. These abutments include ears 12%, having threaded openings in which are engaged screws 122. The abutments are thus adjustable laterally inwardly of the channel, with one screw being adapted to engage link and the other screw being disposed at the opposite side of the toggle and being adapted to engage link 1432'.

At one end of the base, there is fixedly mounted upon the base an upwardly projecting abutment support memher 124, having a threaded opening in which is engaged a screw 126 formed with a reduced, axial extension 1128- disposed in the same vertical plane with extension 58 of screw 56 (see FIG. 1). The axial extensions I28, 58 form abutments at opposite sides of the toggle, engaging correspondingly opposite sides of the link 162 during movement of the main slide through its working stroke and return stroke respectively, that is, its movements first to the right in FIG. 1 and then to the left in the same figure of the drawing.

A lead. screw 134 is journalled in bearings 13%) and 132 on the ends of the base 12. The lead screw must be driven by the same source of power as the drive spindle to which the work piece is attached. The two must be positively geared together by gears to give the exact.

desired ratio between the r.p.m. of the spindle and the rpm. of the lead screw with no chance for slippage.

Referring to FIG. 5, in embracing relation to the screw, but completely out of contact therewith, is a U-shaped supporting bracket 136 fixedly secured to the main slide 30 for movement therewith longitudinally of the screw. Supporting bracket 136 has its outer leg secured to a supporting arm sectionally constituted by members 138, 140 fixedly secured to each other and extending longitudinally of the screw as shown in FIG. 1. To the forward end of the member 140 there is secured the inner end of a laterally outwardly projecting U-shaped bracket 142 on which is mounted a solenoid 144, the core of which projects toward the screw. Secured to the projecting end of the core is a half-nut 145, threaded complementarily to screw 134. When the solenoid is energized, the core thereof is projected outwardly to engage the half-nut threadedly with the screw 134.

The adapter is used to attach the device to a ma chine and as previously noted herein, all portions or components of the device must be fastened to or above the base, which is a relatively thin piece as seen from the side. The controls may be attached to a projecting plate or shelf cast integral with the main slide and this plate would provide ample room for mounting the limit and opening switches one above the other and a commutator above or on the shelf. Of course, the commutator shaft passes through the shelf in such an arrangement to hold the teeth of the gear carried thereby in contact with the lead screw. Secured under the shelf and to the same would be the holding switch, the relay or contactor, and the solenoid.

The solenoid would be of the push type and pushes the half-nut into contact with the lead screw. Various arrangements might be employed, alternatively. For example, it might be decided to use two half-nuts as in a lathe, in which case a link connection would be used. When the half-nut is pushed in it compresses a spring (not shown) which would pull the half-nut out of engagement when the solenoid is deenergized, at the end of the cutting stroke.

Adjacent the bearing projection 132, a gear wheel 148 is in mesh with the screw 134, and rotates on an axis perpendicular to that of the screw. The gear wheel 148 is keyed or otherwise secured to a pin 146 which projects above the gear wheel as seen in FIG. 2, and which also has a reduced extension extending below the gear and rotatably bearing in a vertically extending bearing sleeve 150 fixedly mounted upon a bracket 152 that is fixedly attached to one side of the base.

Referring to FIG. 2, the pin 146 is of non-electrically conductive material, as for example plastic, and embedded in the surface of the pin and extending longitudinally of the pin, above gear 148, is bridging element 154 of electrically conductive material, bridging spring contacts or brushes 156, 158 that are anchored to the base. The pin and element 154 constitute a commutator.

The invention contemplates use of a limiting switch 164, normally closed and an opening switch 166, normally closed, mounted on a stationary portion of the base. These switches are shown diagrammatically in FIG. 9, and are actuated by adjustable screws 168 and 170, respectively, carried on an extension of support 124.

Referring to FIG. 9, the electric current flows from the main or house supply to the normally closed limit switch 164 to opening switch 166. Switch 166 will be closed after main slide '30 begins to move back after opening the circuit momentarily at the normal end of the stroke. From switch 166 the current passes through two circuits. One circuit including the switch 53, brush 156, commutator 146, brush 158, to relay coil 162 to the source. Energization of the coil 162 provides the solenoid 144 with some initial movement. This initial movement of the solenoid closes the holding switch 135 and the current will pass through said switch 135, relay 54 holding the switch of the relay closed and allowing the main slide carrying the solenoid 144 to complete its stroke when the actuating screw opens switch 166.

The circuit is such that the half-nut will be permitted to engage the threads of screw 134- only when the threads of the half-nut are in exact, meshing relation to the threads of the lead or advancing screw. This is the purpose of commutator or brush-type electrical contact provided by the geared dial 148. The principle is the same that used on modern engine lathes. In other words, even though the circuit might be otherwise closed, the half-nut is not permitted to move into engagement with the threads of the screw 134 unless and until the contacts 156, 158 are bridged by the element 154. They will be so bridged, of course, only when the gear 148 is in a predetermined position relative to the lead screw and at this particular time, the half-nut can be advanced into engagement with the threads of the lead or advancing screw.

In any event, in operation of the device, it will be assumed that the work piece has been advanced to the proper position, and is rotating. The main slide 30, thus, in FIG. 1 is in its initial or starting position, with the contact 38 of switch 53 engaged by screw 36.

At this time, the knob 112 is manually rotated to rotate cam 116 to a selected position with its cam face; in en agement with the rear plate or end plate 76 (FIG. 8) so that plate 76 is forced inwardly. This adjustably locates the slide 80, and in turn causes a correspondingly adjusted location of the slide 78 for initial operation. When the main slide 30 reaches its initial or starting position, the free end of the abutment pin 58 engages link 162, straightening out the toggle and thereby causing slide 78 to be advanced to a greater extent than slide 80, advancing the bit a selected extent into engagement with the work. There is thus a rigid connection between plate 76 and the work piece 90 thereby maintaining the links and 102 in straightened condition. Switch 53 is closed at this point, by depression of the contact 38, and assuming that the contacts 156, 158 are bridged, solenoid 144 is energized. The half-nut engages screw 134, and as a result the main slide is shifted to the right in FIG. 1.

Since the work piece 90 is rotating, this produces a helical thread in the work piece.

As the slide finishes its return stroke, the links are straightened out, with the operation being finished just at the end of the stroke. The toggle 100 at the end of each pass is straightened by pine 56 and brought to bear against the adjusting stop or screw 122, the position being such as related to the central pivot pin 104 to move it just past center, the return springs 84 pressing against the cross slide 14 and holding the toggle members rigidly in line until the pin 126 engages the toggle at the end of the stroke and causes the toggle to collapse, thus retracting the cross slide.

Eventually, when the thread has been completed to the desired extent, the abutment pin 128 will engage the right-hand side of link 102, viewing the same as in FIG. 1. At the end of each forward stroke the opener or pin 128 will open the toggle. The cutting tool must be moved completely out of the thread or cross threading will result in spoiling the thread on the return stroke. This will cause the links 100, 102 to move into an angular relationship to one another. As a result, slide 78 will be retracted, moving the bit out of engagement with the work in a direction radially outwardly from the work.

At the same time, as the main slide finishes its travel on the cutting stroke, the lug or block 52 on belt 40 will engage arm 28 of switch 22. This will cause the arm to be rocked, opening the normally closed switch 22. This will temporarily open the circuit through the solenoid, so that the core of the solenoid retracts, disengaging the half-nut from the screw 134, whereupon the pull of the weight 50 on belt 40 will accordingly cause the main slide 30 to be returned to its initial, starting position, and when it reaches said position, switch 53 will again be closed by.

screw 36 engaging switch button 38, starting the cycle all over again.

The construction is designed to insure progressive advancement of the bit radially inwardly of the work, during successive passes along the threads. This provides for more accurate threading of the work and for a cleaner thread groove. The design is such that the first cut, particularly for a V-type thread, should be relatively deep, as the amount of metal removed for a given feed is smaller than in later cuts where the width of the cut materially increases. Further, at this stage, finish is unimportant. The knob 112 is rotated manually to reset the tool at the end of each complete thread or the beginning of a new one to adjust the depth of the thread. It is often desirable to have the finishing cuts relatively light with perhaps the final pass being made without any feed, to insure a smooth finish thread. From start to finish of a complete thread including the individual passes, the operation is completely automatic.

The cam 116, acting in conjunction with the ratchet wheel 114 and the pawl 66, accomplishes this operation. The function of the pawl 66 is to engage the desired number of teeth of the ratchet wheel 114 near the end of the return stroke, rotate the wheel and the feed cam 116, the desired depth for the ensuing cut, and repeat this operation for each stroke, until the thread is cut progressively deeper, until completed when a deep cut in the cam 116 will allow the slide to retract by pressure of spring 94. The slide 80 and hence the slide 78 are initially set by rotation of the knob 112, at the end of each complete thread or at the beginning of a new thread, moving slide 80 a selected distance away from the end plate 76 to a pre-fixed stop. The knob may however be rotated against an adjustable stop for quick action and if required for long runs the setting could also be automatic. On each pass, over the same threads of work piece 90, a deeper cut is to be made. Accordingly, each time the main slide is moved through its return stroke back to its initial, FIG. 1 position, the pawl 66 will be brought into engagement with the ratchet wheel 114, turning said ratchet wheel through a given number of degrees. Cam 116 is, accordingly, correspondingly turned. Therefore, the cam will be progressively moved to successively following positions in which its periphery is at a greater radial distance from its axis. This causes a corresponding, progressive movement of slide 80 toward the work piece. Slide 78 is therefore correspondingly moved, on each pass of the work, slightly closer to the work piece Eventually, as the cam reaches the position shown in FIG 8, the periphery of the cam remains at a constant radius from the axis of the cam, rather than continuing in its spiral. The final pass is thus made without any further feed of the bit into the work, to clean out the thread previously formed in the work. Then, on the next pass, the cam moves to a position in which its abutment or step 118 shifts away from the adjacent end plate, bringing the low end of the peripheral cam surface into engage- 10 ment with the thrust or end plate to retract the slide and slide 78 to their initial position for acting on another work piece, which may be automatically moved into position simultaneously with removal of the work piece previously finished.

It will be understood that in some commercial embodiments, it may be desired to use a cam traverse, which would be better than the lead screw illustrated, for certain conditions.

While I have illustrated and described the preferred embodiment of my invention, it is to be understood that I do not limit myself to the precise construction herein disclosed and that various changes and modifications may be made within the scope of the invention as defined in the appended claims.

Having thus described my invention, what I claim as new, and desire to to secure by United States Letters Patent is:

1. In a thread-chasing apparatus having a base and a carriage slidable on the base, mechanism for effecting reciprocation of the carriage, comprising a feed screw supported on the base, a half-nut follower on the carriage having threads engageable with threads of the feed screw during rotation of the feed screw and when the threads of said feed screw and half-nut are in alignment, a solenoid on the carriage having a core mounting the half-nut for extension of the half-nut into and out of engagement with the feed screw responsive to energizing and deenergizing of the solenoid, a commutator driven in timed relation by the feed screw and switches in circuit with the solenoid controlled by said commutator for energizing and deenergizing the solenoid, said commutator having a bridging element completing the circuit of said solenoid.

2. In a thread-chasing apparatus having a base and a carriage slidable on the base, a mechanism according to claim 1 further comprising switch means in circuit with the solenoid and operable responsive to movement of the carriage to opposite ends of its path of reciprocation, said switch means being adapted for energizing the solenoid at one extreme limit of movement of the carriage and for deenergizing the solenoid at the other extreme limit of the carriage movement, said switch means including one switch, said one switch being mounted on said base and including a switch contact, and a lug on the carriage engageable with said contact to operate said one switch when the carriage reaches one extreme limit of its travel.

References Cited in the file of this patent UNITED STATES PATENTS 2,527,397 Castelli Oct. 24, 1950 2,565,020 Christman Aug. 21, 1951 2,581,082 Drissner Jan. 1, 1952 2,622,252 Wernli Dec. 23, 1952 2,778,037 Renoux Ian. 22, 1957 FOREIGN PATENTS 346,617 Great Britain Apr. 16, 1931 1,073,701 France Mar. 24, 1954

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