US2769991A - Threading machine having spindle feed means and spindle return means - Google Patents

Description

Nov. 13, 1956 c. H. LAEMMEL 2,769,991 THREADING MACH INE HAVING SPINDLE FEED MEANS AND SPINDLE RETURN MEANS Filed Nov. 18. 1952 4 Sheets-Sheet l A 72 INVENTOR. T x B 6% W 2 y I Nov. 13, 1956 c. H. LAEMMEL 2,769,991

THREADING MACHINE HAVING SPINDLE FEED MEANS AND SPINDLE RETURN MEANS 4 Sheets-Sheet 2 Filed NOV. 18, 1952 INVENTOR.

Nov. 13, 1956 H LAEMMEL 2,769,991

C. THREADING MACHINE HAVlNG SPINDLE FEED MEANS AND SPINDLE RETURN MEANS Filed Nov. 18, 1952 4 Sheets-Sheet 3 INVENTOR.

E2 @ZM W Patented Nov. 13, 1956 THREADING MACHINE HAVING SPINDLE FEED MEANS AND SPINDLE RETURN MEANS Charles H. Laemmel, Dayton,

Sheifield Corporation, Ohio Ohio, assignor to The Dayton, Ohio, a corporation of This invention relates to threading apparatus.

One object of the invention is the provision of a unitary threading unit for use with a workpiece holder, and of compact and rugged construction and which is simple and accurate in its operation.

Another object of the invention is the provision of a threading unit of the character referred to which can perform completely automatic threading operations or which can be readily adapted to manual control.

Another object of the invention is the provision of a threading unit of the character referred to which has a positive lead control for spindle advance upon rotation by a drive means and which includes a controllably operable return drive.

Another object of the invention is the provision of a positive lead control which includes a lead screw on the tool carrying spindle associated with a controllable lead nut means.

Another object of the invention is the provision of a positive lead control of the character referred to which is readily accessible and which is quickly removable for insertion of lead control components.

Other objects and advantages of the invention will be apparent from the following description, the appended claims, and the accompanying drawings, in which,

Figure l is an overall perspective view showing a threading unit embodying the present invention associated with a workpiece holder and a platform,

Figure 2 is a longitudinal view of the threading unit certain parts being shown in central vertical section,

Figure 3 is a section through the return drive mechanism but showing the return sleeve in an advanced position,

Figure 4 shows the oiling system for the unit,

Figure 5 is a view in partial section of the drive sleeve for rotating the tool carrying spindle,

Figure 6 is a view in partial section, broken along its length, of the tool carrying spindle,

Figure 7 is a top plan view of the rear end of the threading unit showing the limit operated switch means and the connection to a lead control yoke member,

Figure 8 is a side view of the rear end of the threading unit showing the removable housing for the lead screw and lead nut means,

Figure 9 is a diagram of the trols, and

Figure 10 is a schematic representation showing generally the overall association of the mechanical and electrical components of an exemplary threading unit.

In the exemplary embodiment of the present invention illustrated there is shown a tool carrying spindle mounted in a compact threading unit having associated therewith a drive unit for rotating the spindle, a return unit for returning the spindle after it has completed a threading operation and a controllable lead means for advancing the spindle upon its rotation by the drive unit. These components can be coordinated automatically or may be subjected to individual manual actuation. As shown, the spindle carries a collapsible die head.

various electrical con- Referring more particularly to the drawings, in which the same reference numerals are used to designate like parts in the several views, the numeral 10 designates a threading unit embodying the present invention carried by any suitable support such as a base or table 11 for cooperation with a work holding structure 12. The threading unit 19 includes a housing 13 which supports on its upper surface a main drive motor 2A which is connected as will be further described for rotation of a tool carrying spindle 16 mounted longitudinally in the housing 13. A return motor 1A is also mounted on the housing 13 and is connected to the spindle 16 to return it upon the completion of a threading operation. The spindle 16, as illustrated, supports an automatically collapsible tap or die head 15. A lead screw 18 is remov ably mounted on the rear end of the spindle 16 and removable lead nut segments 19 are carried in the rear end of the housing 13 for cooperation with the lead screw to advance the spindle 16 axially upon its rotation by its drive motor 2A.

The spindle 16 has a tool mounting flange 21 at its outer end, is rotatably and slidably carried in the housing 13, and extends therethrough. As shown in Figure 6 the spindle unit 16 has portions 22, 23 and 24 for the mounting respectively of a drive unit sleeve, a return sleeve, and a lead screw. Oil grooves 25 are provided in its outer surface for the lubrication of the sleeves.

The lower portion of the unit housing 13 forms an oil reservoir A cam driven lubrication pump 29 is located in this reservoir for supply of lubricating oil through conduit 30 (see Figure 4) and branch 39 to the rear bearing 51 and an intermediate portion of the spindle axis respectively. If desired an additional conduit can be utilized for the lubrication of the lead unit in the rear of the unit housing. An oil retaining ring 14 seals the forward end of the housing 13 relative to the drive sleeve 36. Oil sealing ring 17 is provided between the drive sleeve 36 and the sliding spindle 16 at their forward ends.

The structure for rotating the tool carrying spindle 16 is more clearly shown in Figures 2 and 5. The main drive motor 2A drives continuously in a single direction in this embodiment through belts 26, a multiple-sheave 28 in the lower portion of the unit, across under the spindle 16, and to a gear 30, which is the drive gear of a set of change speed gears 30, 31 and 32. The gear 31 of this set is mounted in a bracket 33 to allow adjustments of the gear 31 when different sets of gears are inserted. These gears are accessible through a removable cover 20. Gear 32 drives a worm 34 which engages a worm gear 35 mounted on the drive sleeve 36 by threaded retaining rings 37 and 38. The drive sleeve 36 is rotatably mounted in the threading unit 10 by bearings 40 and 41. The drive sleeve 36 also supports the spindle 16 which is slidably mounted therein. A radial drive pin 43 projects through a slot 42 in the drive sleeve and is threaded into the spindle at 44 for rotation thereof but allows axial sliding of the spindle 16 within the drive sleeve 36. The drive sleeve 36 has internal oil grooves 45 and has threaded sections in its outer surface at 46, 47 and 48 for the mounting of the bearing retaining rings 37 and 38 and a retaining ring 49 for the inner race of the rear bearing 41.

Next situated along the length of the spindle 16 is a return sleeve 50 which abuts a bronze washer 59 be tween it and a shoulder on the spindle and which is retained against axial movement relative to the spindle at its inner end by a bearing 51, a sleeve 52, and a retaining ring 53 threaded onto the spindle 16 at 54. The sleeve 52 is keyed to the spindle 16 at 55, shown in Figure 6 and cooperates with an oil retaining ring 63 mounted in the housing.

The return motor 1A drives through a chain 56 to a sprocket 57 enclosed in a removable housing bolted on the unit and indicated at 58. The sprocket 57 which is driven continuously in a counter-clockwise direction as viewed from its left-handface in Figure 3 once the motor 1A is energized, drives through a controllable planetary clutch unit 60 to a pinion 61 which engages a rack 62 extending along the return sleeve 50.

The sprocket 57 is keyed to a shaft 64 which in turn has a driven sun gear 65 keyed thereto at its inner extr'emity. Planetary pinions 66 mesh with sun gear 65 and are carried by an annular member 67 which is keyed at 68 to a shaft 69 which extends transversely through the threading unit. An internal gear 70 meshes with the planetary pinions 66 and is mounted in an annular member 71 journaled about the shaft 64. About this annular member 71 is a brake band 72 controlled through a member 73 actuated by solenoid means referred to later. About the annular member 67 which supports the pinions 66 is another brake band 74 controlled by a member 75 which is also solenoid actuated. Upon tightening of brake band 72 (with band 74 held released) the sun gear 65 will drive the planetary pinions to planetate them along stationary internal gear 70,. carrying with them the annular member 67 upon which they are mounted, and driving the return sleeve 50 for return of the spindle 16. When member 75 is actuated to close brake band '74 (with band 72 held released allowing annular member 71 to be rotated by pinions 66 without transmitting a driving torque) the return pinion 61 and its meshing rack 62 are also braked, thereby preventing longitudinal movement of the spindle 16. This latter structure permits vertical mounting of the threading unit. With both bands released the planetary gear clutch unit is in an idle condition, neither transmitting a drive torque nor braking the output shaft. The shaft 69 is mounted in the unit housing 13 by bearings '77 and 78 and has oil retaining rings 79 and 86 adjacent the respective ends thereof. The shaft 69 extends outward through a fitting 76 on the housing 13 and has a projection provided at 81 for the insertion of a handle should it be desired to manually position the spindle 16.

If desired, return could be achieved by leaving the lead nut segments engaged and using a reversible main drive motor.

A radial projection 82 is threaded into an enlarged portion 84 of the return sleeve 50 and is carried with said sleeve 50 when it is moved with the spindle upon its threading operation and return. At its outer end projection 82 is inserted into a member having two portions forming longitudinally extended support elements 86 and 87. These elements 86 and 87 are shown in section in Figure 3, in a side view in Figure 2, and in a plan view in Figure 7. Elements 86 and 87 are also carried as the spindle moves axially and the member of which they form the major portion is mounted for such movement in guide rails 88 and 89 fixed on the housing wall. Carried on these longitudinal support elements 36 and 87 are adjustable limit projections 90 and 91. Knobs 93 and 94 are provided respectively on limit projections 90 and 91 for manual adjustment of each of these projections upon the longitudinal elements 86 and 87 thus con-trolling their association with an electrical circuit switch means later described in detail. These switch means control the return drive brake bands and the actuation of the lead nut segments at the selected forward and rearward limits of spindle operation.

A lead screw 18 is mounted on the inner end of the spindle 16, is keyed thereto by a key seated in the spindle at 96 (see Figure 6) and is retained on the spindle by a retaining ring 97. At its forward end screw 18 abuts a washer 92 which contacts an abutment on the spindle. A lead nut mounting component 98 is fixed to the unit wall at 9 9. Radially mounted in this component 98 for engagement with the lead screw 18 are lead nut segments' 19 preferably three in number. Radially situated springs 100 engage pins 101 in each of the lead nut segments urging the segments radially outward. Axiall'y slidable on the component 98 is a lead nut control sleeve 102 urged axially outwardly in the exemplary embodiment illustrated by springs shown at 104. This lead nut control sleeve 162 has a cam 105 on its inner surface. This sleeve is moved to engage and disengage the lead nut segments 19 with the lead screw 18 and is actuated by a yoke member 106 which has projections seated therein at 163. The yoke 106 is pivoted about a fixed point 128 (see Figure 10). It will be apparent that the yoke 106 could be easily adapted for manual actuation if desired.

A general association of the yoke control is shown in Figure 7. Rollers 167 and 1138 are mounted on the switch units 109 and 116 for engagement with the respective limit projections 96 and 91 at the adjusted extremes of desired spindle movement. Roller 107, which is actuated by the forward limit, controls through a switch unit 169 a pull solenoid shown at 5A. Roller 198 actuates a double throw switch 110 to energize push solenoid 3A. The details of the electrical circuits are later explained in connection with Figure 9. Solenoids 3A and 5A have armatures which are connected together and to a bar 113. This bar 113 is connected to a yieldable connection 114 fastened to one end of the yoke 106. Connection 114 will allow positive actuation of the yoke 196 to move the sleeve 102 to the left as viewed in Figure 7 and allow radial projection of the segments 19 by the springs 160 to disengage the segments from the lead screw 18. When the push solenoid 3A is engaged the yieldable connection 114 allows a limited pro-loading in order to prevent forceful engagement of the lead nut segments 19 with the lead screw 13 by the inner cam surface 105 before the nut and screw elements are properly aligned.

In Figure 8 is shown the removable housing sections for the lead unit. With the components of the lead control unit located at the rear end of the threading unit 10 they are readily accessible by removing the upper component 116 of the removable housing. After removing the upper component 116 the retaining ring 97 can be unscrewed annd removed, the spindle advanced, and the lead screw and lead nut segments can be easily removed and replaced. This structure allows the insertion of cooperating pairs of lead screws and lead nuts to obtain various leads as desired.

In Figure 10 is shown a schematic arrangement of the major components of the threading unit and their association relative to the spindle 16 when it is at its rearward position as shown in that figure. The spindle 16 has a tool holding flange 21 at its outer extremity and spaced along its axis, in order, the drive sleeve 36, the return sleeve 50, the lead unit 102 supporting the lead nut segments and the lead screw 18. The planetary gear clutch unit is shown at 68. Mounted on top of this unit are solenoids 6A, 4A (see Figure 10) which are onclosed in a housing shown in Figures 1 and 2. Solenoid 6A is attached to member 73 in Figure 3 and actuates the return brake 72. Solenoid 4A is attached to member 75 of Figure 3 and actuates the brake 74 which prevents spindle movement. Solenoid 6A is a pull solenoid and closes brake 72 which is normally biased in a releasing position. Solenoid 4A is also a pull solenoid and when energized releases brake 74 which is normally spring biased closed. Yoke 106 which actuates the lead nut segments 19 is pivoted at its upper end 128 and has a projection 129 which cooperates with a switch 120.

Figure 9 shows the electrical circuit embodying the various controls for the threading unit. Power is supplied through connections 131. Relays in the secondary transformer circuit control switches in that circuit and also actuate switches situated to control components energized from the main line. The relays are numbered 1 through 6 and the switches actuated thereby are correspondingly numbered with small letter subscripts.

The operation of the threading unit is set forth below with particular reference to Figure 9 which shows the wiring circuit above referred to when the spindle is in its rear position and Figure 10 which shows the association of the various components.

The master stop switch 122 is normally closed, as shown. Closing the start switch 121 for the return motor 1A energizes relay 1 to close switches 1a and 11), starting the return motor 1A and setting up the circuit for the other controls. Stop switch 124 is normally closed and rear limit contacts 110a are closed by double throw switch 110 when the spindle occupies its rear position at the start of a threading operation. Accordingly when main drive motor start switch 123 is closed relay 2 is energized to close switch 2a, starting the drive motor 2A. Switch 2b in the secondary circuit is also closed to set up the circuit to relays 2 and 3 around contacts 110a and 123. Thus upon engagement of cycle start switch 125, relay 3 is energized through normally closed switch d to close switch 3:: thus energizing push solenoid 3A to close the lead sleeve and engage the lead nut segments. Switch 3b is closed around the cycle start switch 125. Switch 3c is also closed to energize relay 4, closing switch 4a, and energizing solenoid 4A to release brake 74. This causes the spindle to advance on a threading operation. The die head 15, illustrated for purposes of example only, has abutment means located on a rod 112 to coordinate its actuation with spindle advance and return through the operating yoke 115.

When the limit projection 90 contacts the roller 107 at the adjusted forward limit of spindle travel it engages and closes switch 109 which is normally open. Lower contacts 110!) are closed (and upper contacts 110a are opened) when the rear limit projection 91 releases the switch 110 upon movement of the spindle from its rear position. Closing switch 109 accordingly energizes relay 5, closing switch 5a to energize pull solenoid 5A, opening the lead sleeve. Relay 5 also opens switch 5d thus de-energizing relay 3 to de-energize push solenoid 3A. Relay 5 also closes switch 5b to keep relay 4- energized and the brake 74 released. Switch 50 is also closed when relay 5 is energized to furnish current to relay 5 When switch 109 is released. When pull solenoid 5A is energized to actuate the yoke 105 for disengaging the lead nut segments the projection 129 thereon engages switch 120, closing same, to energize relay 6 which in turn closes switch 6a to energize solenoid 6A. Solenoid 6A closes brake 72 and returns the spindle. This se quence of return operations is necessary in order to prevent return movement of the spindle before the lead nut segments are fully disengaged. Solenoid 4A is held energized through switch 5b controlled by relay 5 thus holding the brake 74 released.

When the rear limit projection 91 contacts roller 108 switch 110 closes upper contacts 110a and opens lower contacts 11017 thereby de-energizing solenoids 6A, 5A and 4A. The spring associated with solenoid 4A closes the brake 74 and holds the spindle against axial movement.

If power should fail at any time during the stroke of the spindle the solenoid 4A will release its spring loaded brake 74 which will engage and hold the spindle in the position it occupies at the time of power failure.

If in the forward stroke trouble should develop and the operator desires to stop forward motion of the spindle, he would push stop button 122. This would shut oft all current and the spindle would be held in position by the spring loaded brake 74. To then return the spindle to its back position, start button 121 would be depressed to start the return motor 1A. If the tool is in cutting position it must be released from the work. The emergency return button 126 is then pushed energizing solenoids 6A and 5A, returning the spindle to its starting position. The main drive motor 2A can only be started when the rear limit projection 91 is engaging the roller 108, closing upper contacts a.

It is thus seen that a threading unit has been provided which is simple and compact in arrangement, that the various components thereof and in particular the lead screw and lead nut unit are readily accessible and can be easily removed and replaced. The association of the lead screw directly on the tool holding spindle with the engageablo lead nut segments gives an extremely accurate and positive advance control in a comparatively simple construction. This direct control of lead by means of a lead screw mounted on the tool holding spindle avoids the errors associated with an intermediate gear drive or the like resulting from lost motion in the gears and errors in their configuration. The location of the lead screw at the rear end of the spindle and the lead nut segments at the rear of the unit housing makes it relatively easy to remove and insert lead screws and lead nut segments for particular operations. The lead nut segments are held positively engaged when the control sleeve is moved to engage them; however, the sleeve is actuated through a yielding pressure to prevent forceful engagement before the lead screw and lead nut segments are properly aligned. A circuit has been provided to give full automatic actuation of the threading operation and provision has been made for emergency conditions. The unit can also be readily adapted for manual actuation of the return and lead unit components.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. A threading machine comprising a threading unit and a workpiece holder, said threading unit comprising a tool holding spindle, means slidably and rotatably supporting said spindle in said threading unit, a holder for a collapsible cutting head fixed to the outer end of said spindle, a driving sleeve fitted coaxially about said spindle adjacent said cutting head holder, means connecting said drive sleeve to said spindle for rotation thereof but allowing relative sliding therebetween, a power drive means including change speed gearing connected to rotate said drive sleeve, a return sleeve coaxially mounted about said spindle adjacent said drive sleeve, abutment means on said spindle at each end of said return sleeve allowing relative rotation of the return sleeve with respect to said spindle but preventing axial movement between these units, a rack extending axially along one side of said return sleeve, a drive pinion engaging said rack, return power means drivingly connected to said pinion, a lead screw mounted on the inner end of said spindle and removably fixed thereto, lead nut segments about said lead screw, means mounting said lead nut segments in said unit in removable relationship thereto and for movement toward and from said lead screw, resilient means urging said lead nut segments radially outward from said lead screw, an annular cam means about the radially outward portions of said lead nut segments for positively engaging said lead nut segments with said lead screw, adjustable limit projections carried by said return sleeve as it moves axially with said spindle during a threading operation, control means for moving said cam means to release said lead nut segments and actuating said return means, in that sequence, after a threading operation, switch means actuated by said adjustable limit projections and connected to said control means for energization thereof at the selected limits of spindle travel determined by said adjustable limit projections.

2. A threading unit for use with a workpiece holder comprising a tool holding spindle, means on said spindle for-detachably connecting a collapsible threading tool,

supporting means for rotatably and slidably carrying said spindle in said threading unit, a drive unit for rotating said spindle in one direction operatively connected thereto, controllable lead means operatvely connected to said spindle, return means having an output drive shaft operatively connected to said spindle, control means connected. to said return means including means to actuate said return means for return drive, means to place said return means in an idle condition and means to brake the output shaft thereof, forward and rearward limit means mounted on said threading unit operatively connected to said spindle and connected to said controllable lead means. and to said return control means, manually operable cycle starting means to activate said lead means and place said return means in an idle condition, means actuated by said forward limit means toplace the lead means in inactive position and actuate the return means, in that sequence, and means actuated by said rear limit means for deactivating the return means and braking the return output shaft.

3. A threading unit for use with a workpiece holder comprising a housing, a tool holding spindle for a collapsible cutting tool, means in said housing carrying said spindle for rotation and for axial movement, drive means for said spindle mounted in a fixed position relative to said housing including a drive connection to said spindle for unidirectional rotation thereof but allowing axial movement of the spindle relative thereto, return power means in said housing for rapid axial movement of said spindle during its continued rotation in said one direction, a lead screw fixed to said spindle, lead nut segments spaced about said spindle and carried for movement inward to engage said lead screw and control advance of said spindle and outward to clear the lead screw, actuating means for controlling movement of said lead nut segments, means connected to said actuating means for releasing said lead nut segments from said lead screw upon completion of a threading operation, and means 'connected to said return means operative upon release of said segments to then energize said return power means to rapidly return said spindle by axial sliding.

4. A threading unit for use with a workpiece holder and in which a rotatable spindle has a precise uniform increment of advance for each spindle rotation, comprising a spindle, means on said spindle for detachably connecting a collapsible threading tool, supporting means carrying said spindle for rotation and axial movement in said unit, drive means on said supporting means operatively connected to said spindle for unidirectional rotation of said spindle, a lead unit including a lead screw fixed to said spindle and releasable lead nut means fixed against rotation on said supporting means for advancing said spindle upon its rotation by said drive unit, power means for applying an axial return force to said spindle, limit means responsive to a predetermined axial position of said spindle and operatively connected to said lead unit for releasing said lead nut means and disabling said lead unit upon completion of a threading operation, and means connected to said power means operative upon release of said lead nut means to then initiate the application of force to said spindle for rapid return by axial sliding.

5. A threading unit for use with a workpiece holder and in which a rotatable spindle has a precise uniform increment of advance for each spindle rotation, comprising a spindle, means on said spindle for detachably connecting a collapsible threading tool, supporting means carrying said spindle for rotation and axial movement in said unit, change speed drive means on said supporting means operatively connected to said spindle for unidirectional rotation of said spindle while allowing axial movement of the spindle relative thereto, a lead screw fixed to said spindle, lead nut segments supported against rotation in said unit and engageable with said lead screw, a. sleeve coaxial with said lead screw and operatively connected to said lead nut segments for engaging and disengaging said segments upon axial movement of the sleeve, power means for applying an axial return force to said spindle, limit means in said threading unit and operatively connected to said spindle, means responsive to said limit means to axially movesaid sleeve to disengage said segments from said lead screw upon completion of a threading operation, and control means connected to said power means operative upon movement of said sleeve and release of said nut segments to then initiate application of force to said spindle for rapid return by axial sliding during continued rotation in the one direction. 7 p

6. A threading unit for use with a workpiece holder and in which a rotatable spindle has a precise uniform increment of advance for each spindle rotation, comprising a spindle, means on said spindle for detachably connecting a collapsible threading tool, means carrying said spindle for rotation and axial sliding movement in said unit, drive means on said supporting means operatively connected to said spindle for unidirectional rotation of said spindle, a lead unit carried in said threading unit at the inner end of said spindle, arranged concentrically with said spindle and operatively connected therewith for advancing said spindle upon its rotation by said drive unit, means to control the operative connection of said lead unit with said spindle including a movable control member, power means for applying an axial return force to said spindle, adjustable limit means mounted on said threading unit and operatively connected to said spindle,

means connecting said adjustable limit means to said lead unit control member for actuation thereof at the adjusted threading limit, and control means actuated by said member after the lead unit is disabled to then initiate the application of force to said spindle for rapid return of said spindle by axial sliding during its continued rotation in said one direction.

7. A threading unit for use with a workpiece holder and in which a rotatable spindle has a precise uniform increment of advance for each spindle rotation, comprising a spindle, means on said spindle for detachably connecting a collapsible threading tool, supporting means carrying said spindle for unit, drive means on said supporting means operatively connected to said spindle said spindle, a lead unit for advancing said spindle upon rotation thereof, said lead unit comprising a lead screw fixed to said spindle, lead nut segments fixed against rotation on said supporting means, means mounting said segments in said threading unit for movement toward and from said lead screw, resilient means in said unit and connected to said lead nut segments urging said segments away from said lead screw, cam means operatively connected to said lead nut segments for positively engaging said segments with for applying an axial return force to said spindle, limit means responsive to a predeterminedaxial position of said spindle and operatively connected to said cam means for actuation thereof to release said segments and disable said lead unit upon completion of a threading operation, and means connected to said power means opera tive upon release of said lead nut segments to then initiate application of force to said spindle for rapid return by axial sliding.

8. A threading unit for use with a workpiece holder and in which a rotatable spindle has a precise uniform increment of advance for each spindle rotation, comprising a spindle, means on said spindle for detachably connecting a collapsible threading tool, supporting means carrying said spindle for rotation and axial movement in said unit, drive means on said supporting means operatively connected to said spindle for unidirectional rotation of said spindle, a lead unit operatively connected to said spindle for advancing said spindle upon its rotation by said drive unit, said lead unit comprising a lead screw rotation and axial sliding in said for unidirectional rotation of a said lead screw, power means fixed to said spindle at one end thereof, a plurality of lead nut segments for threaded engagement with said lead screw, means mounting said lead nut segments in said threading unit spaced about said lead screw, fixed against rotation and carried for movement toward and from the screw, resilient means in said threading unit connected to said lead nut segments urging said segments away from threaded engagement with said lead screw, a sleeve movable along the axis of said spindle and having cam means on its inner surface in contact with outer portions of said segments for positive engagement of said segments with said lead screw upon axial movement of said sleeve in one direction, power means for applying an axial return force to said spindle, limit means responsive to a predetermined axial position of said spindle and operatively connected to said sleeve for movement thereof in the other direction for releasing said segments and disabling said lead unit upon completion of a threading operation, and means connected to said power means operative upon releasing movement of said sleeve and retraction of said segments from threaded engagement with said screw to then initiate application of force to said spindle for rapid return by axial sliding.

9. A threading unit for use with a workpiece holder and in which a rotatable spindle has a precise uniform increment of advance for each spindle rotation comprising a tool holding spindle for a collapsible cutting tool, supporting means carrying said spindle for rotation and axial movement in said unit, drive means operatively connected to said spindle for unidirectional rotation thereof, a lead unit for advancing said spindle upon spindle rotation, said lead unit comprising a lead screw carried coaxially with said spindle, lead nut means, means mounting said lead nut means in said threading unit for disengagement and engagement with said lead screw, means operatively connected to said lead nut means for control thereof, power means for applying an axial return force to said spindle, means for actuating said power means for return of said spindle, forward limit means mounted on said threading unit and operatively connected to said spindle, means actuated by said forward limit means and connected to said lead nut control means to disengage said lead nut means and means responsive to disengagement of said lead nut means to energize said power actuating means to then initiate application of force to said spindle for rapid return by axial sliding, whereby sequential disengagement of said lead nut means and activation of said return power means is achieved in that order.

10. A threading unit for use with a workpiece holder and in which a rotatable spindle has a precise uniform increment of advance for each spindle rotation, comprising a spindle, means on said spindle for detachably connecting a collapsible threading tool, supporting means for rotatably and slidably carrying said spindle in said threading unit, a drive unit for rotating said spindle operatively connected thereto, a lead unit for advancing said spindle upon rotation thereof, said lead unit comprising a lead screw operatively connected to said spindle, a lead nut segment, means mounting said segment in the threading unit for movement toward and from said lead screw, resilient means mounted in said threading unit and connected to said lead nut segment for urging said segment away from said lead screw, cam means operatively connected to said lead nut segment for positively engaging said segment with said lead screw, a control connection to said cam means including opposing abutment means, resilient means between said abutment means providing a limited amount of yielding therebetween, whereby said resilient means yields when said connection is moved to initially engage said lead nut segment with said lead screw, following which the abutment means engage and the cam means is positively actuated for positive engagement, and means to disengage said lead nut segment from said lead screw and thereafter return said spindle.

11. A threading unit for use with a workpiece holder and in which a rotatable spindle has a precise uniform increment of advance for each spindle rotation, comprising a spindle for a collapsible tool, supporting means carrying said spindle for rotation and axial movement in said unit, drive means operatively connected to said spindle for unidirectional rotation thereof at variable speeds, a lead screw fixed to said spindle, a lead nut segment, means mounting said segment substantially radially with respect to said spindle for movement toward and from said lead screw for controlled advance thereof upon lead screw rotation, resilient means in said unit operatively connected to said segment urging said segment away from said screw, an axially movable sleeve having cam means on its inner surface in contact with an outer portion of said segment, a control connection to said sleeve having a spring means therein for yieldingly moving said sleeve to engage said segment with said screw, return power means for applying an axial return force to said spindle, limit switches operatively connected to said spindle, electrical actuating means connected to said control connection and said limit switches to move said sleeve and release said segment at a predetermined spindle position, and means connected to said return power means operative upon disengagement of said segment from said lead screw to then initiate application of force to said spindle for rapid return by axial sliding.

References Cited in the file of this patent UNITED STATES PATENTS 92,682 Whipple July 13, 1869 1,666,732 Brophy Apr. 17, 1928 2,501,298 Winchell Mar. 21, 1950 2,551,517 Webb May 1, 1951 2,581,082 Drissner et al Jan. 1, 1952 2,622,252 Wernli Dec. 23, 1952 2,637,052 Woock May 5, 1953 2,660,738 Hieber Dec. 1, 1953

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