US3521894A

US3521894A - Air chuck having air distributing valve

Info

Publication number: US3521894A
Application number: US769141A
Authority: US
Inventors: Girard S Haviland; Donald J Mccarthy
Original assignee: Jacobs Manufacturing Co
Current assignee: Jacobs Vehicle Systems Inc
Priority date: 1968-10-21
Filing date: 1968-10-21
Publication date: 1970-07-28
Anticipated expiration: 1987-07-28
Also published as: GB1273276A; FR2021110A1; DE6939497U; GB1273275A

Description

July 28, 1970 G. s. HAVILAND ETAL 3,521,394

AIR CHUCK HAVING AIR DISTRIBUTING VALVE} Filed Oct. 21, 1968 5 Si1eLQ 'heet 3 3 53 5 INVENTORS \5 G/AAPD 5. H/YV/LA/VD 004 410 0 MCC'APTHT ATTORNEY July 28, 1970 G. s. HAVILAND ETAL 3,521,394

AIR CHUCK HAVING AIR DISTRIBUTlNG VALVE 5 Sheets-5heet Filed Oct. 21, 1968 y 1970 s. s. HAVILAND ETAL 3,521,894

AIR CHUCK HAVING AIR DISTRIBUTINQ VALVE Filed Oct. 21, 1968 3 Sixwets-$heer d FIG] United States Patent 01 lice A 3,521,894 PatentedJuly 28, 1970 US. Cl. 2794 10 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an air chuck mountable to a hollow spindle of a lathe machine, having a pneumatically operable piston adapted when moved in one direction to shift a collet actuating sleeve to pressurize a collet into gripping relation with a workpiece and to lock it in such condition, and adapted when moved in the opposite direction to shift the actuating sleeve to relaxed condition so as to release the gripping condition of the collet relative to the work. Operating air is selectively applied to one or the other ends of the piston through a distribution valve. The latter is pneumatically shiftable between a pair of stationary cam elements which cooperate with the valve each time it is shifted to angularly index the valve 45. The valve has a return or normal position in which air-flow distribution ports are out of register with passages leading to opposite ends of the piston chamber. Each time the valve is shifted from this normal position it is caused to register air feed ports with one end of the piston chamber and vent ports with the opposite end of the piston chamber. Shifting of the valve in cooperation with the cam elements operates to angularly index the valve 45 so that the feed and vent ports are connected alternately to oposite ends of the piston chamber. The air supply line is connected through a single passage swivel joint with passages leading through the body of the chuck to the distribution valve.

BACKGROUND OF THE INVENTION This invention relates to the art of rotating air chucks; and its general objective is to provide an improved and compact chuck of this nature.

Air supplied to rotating air chucks is required to pass through a swivel joint. For this purpose, conventional air chucks use a double passage swivel.

In the present invention, an air driven piston is employed to effect gripping and relaxing of the chuck relative to the work. Air feed for the piston is provided through a single passage swivel joint to a distributing valve which operates automatically to alternately feed the air to, and vent it from, opposite ends of the piston chamber.

The distributing valve is one feature of this invention. It is of a small and compact size, incorporated in the body of the piston. It makes possible the employment of a single passage swivel joint in the feed line. The single passage swivel is less complex in its structure than a double passage swivel. Because of its single passage, it is relatively smaller in diameter and overall size and has less parts. Accordingly, its speed rating is relatively greater; and its cost is substantially less. A further advantage of the single passage swivel is that it can be used with a three-way feed control valve; whereas, the double passage swivel is used with a four-way feed control valve.

The overall air chuck is another feature of this invention. It represents a decided technical advance in the art of air chucks because of the multiple advantage obtained by it.

BRIEF DESCRIPTION OF DRAWINGS In the accompany drawings:

FIG. 1 is a rear end view in elevation of an air chuck embodying the invention;

FIG. 2 is a section on line 22 of FIG. 1; the broken line portion at the left representing a hollow driving spindle;

FIG. 3 is a fragmentary detail of FIG. 2 showing the chuck with its components in gripping condition;

FIG. 4 is a fragmentary detail of the rear face of the piston;

"FIG. 5 is a section on line 5-5 of FIG. 4;

FIG. 6 is a section on line 66 of FIG. 4;

FIG. 7 is a section on line 7'7 of FIG. 4;

FIG. 8 is a fragmentary section on line 88 of FIG. 2;

FIG. 9 is a detail in side elevation of the left cam member;

FIG. 10 is a right end view of FIG. 9;

FIG. 11 is a section on line 1111 of FIG. 10;

FIG. 12 is a detail in side elevation of the right cam member;

FIG. 13 is a left end view of FIG. 12;

FIG. 14 is a section on line 1414 of FIG. 13;

FIG. 15 is a detail in side elevation of the indexing valve;

FIG. 16 is a right end view of FIG. 15;

FIG. 17 is a section on line 1717 of FIG. 16; and

FIG. 18 is a section on line 18-18 of FIG. 16.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The air chuck 10 shown in the drawings as embodying the invention is adapted to be rigidly mounted to an openended driving spindle 11 of a machine lathe by means of a set of mounting lugs 12 (FIGS. 1, 2) projecting from the rear face of the body 13 of the chuck. The chuck body has an axially extending cylindrical horn 14. An axial bore through the chuck body enlarges conically to define a coned recess 15 which opens out of the forward end of the horn.

The recess 15 is adapted to accommodate a conventional coned resilient contractible collet 16. The collet has a work receiving opening 17 defined by a ring of radially extending tapered metal jaws 18 bonded to one another I by rubber material 19. The collet is receivable partway into the recess without contraction of its jaws. When the collet is pressured further into the recess, its jaws contract into gripping relation with a workpiece 21 received therein; and when the pressure on the collet is relaxed, its jaws automatically restore to released condition relative to the work upon expansion of the resilient bonding material 19.

A nosepiece 22 is cooperable with the collet to pressure it into the recess. The nosepiece has an annular body 23 slidably disposed upon the chuck horn 14; and has an inturned annular flange 24 fronting the marginal areas of both the coned recess and the collet. An inner beveled surface 25 of the flange 24 is adapted to abut a corresponding beveled surface of the collet as the nosepiece is moved rearwardly along the chuck horn. A key 26 fixed in the surface of the chuck horn is slidable in a longitudinal keyway 27 of the nosepiece to limit the latter to axial movement along the horn and to restrain it against relative rotation.

The nosepiece has a threaded connection 28 with a sleeve 29. An inner diameter surface 31 of the sleeve located rearwardly of the threaded connection 28 slidably bears upon the surface of the chuck horn. Since the nosepiece is limited by the keyway 27 to axial movement, rotation of the sleeve about the chuck horn will cause axial movement or adjustment of the nosepiece relative to the collet, accordingly as the sleeve is rotated in one direction or the other.

Spring loaded detent pins 32 (FIGS. 2, 8) slidable in and out of axial holes 33 in the rear end wall of the sleeve 29 are cooperable with shallow pockets 34 formed in an annular radial shoulder 35 of the chuck body to frictionally retain the sleeve in selected angularly rotated positions. The holes 33, one of which is shown in FIG. 2, are spaced angularly and equally apart; in each of which a detent pin 32 is biased axially outward by means of a detent spring 36. Here, there are four detent pins. There is, however, a greater number of the detent pockets 34, as appears in FIG. 1, so that a relatively fine angular adjustment of the sleeve and as a consequence a desired axial adjustment of the nosepiece relative to the collet may be obtained with each predetermined angular increment of adjustment of the sleeve. A group of notches 37 are provided in the external end wall of sleeve 29, to which notches a spanner wrench may be applied for effecting angular adjustments of the sleeve. As the sleeve is rotatively adjusted, the detent pins 32 are forced to ride in and out of successive pockets 34 until a selected angular adjustment of the sleeve is obtained. The engagement of a spring loaded detent pin with one of the pockets in a final adjustment of the sleeve will frictionally restrain the latter from creeping angularly from its adjusted position during normal operation and vibration of the chuck. The adjustment made in the sleeve will be such that the workpiece 21 may be loosely entered into the collet; and when the sleeve is caused to be moved axially rearward for a short distance it will act through the nosepiece to pressure and contract the collet into gripping relation with the workpiece.

The adjusted sleeve 29 has a forward normal position as in FIG. 2 in which it is normally held under the bias of the expanded detent springs 36. In this position, the pressure of the nosepiece 22 upon the collet 16 is relaxed so that the collet has a non-gripping relation to the workpiece. To obtain a gripping condition of the collet with the work after the nosepiece has been adjusted, it is only necessary to move the sleeve rearwardly sufiiciently to cause the nosepiece to pressure the collet and contract its jaws into gripping relation with the work.

Forward or rearward movement of the sleeve and, as a consequence, of the nosepiece so as to grip or loosen the collet about the work is selectively controlled by means of a pneumatically operable piston 38. The piston is reciprocable in an annular chamber 39 (FIG. 2) defined about the chuck horn by means of a cylinder 41. The cylinder has an annular rear end wall 42 which is bolted to the inner face of an annular radial flange 43 of the chuck body. An inturned radial flange 44 at the front end of the cylinder has an annular internal wall 45- providing a bearing surface for the periphery of the sleeve 29. Seal rings at opportune points seal the ends of the chamber fluid tight.

The piston 38 is of annular form. It has a pair of end lands 48 and 49 about its periphery which bear upon the internal surface of the cylinder 41 as the piston reciprocates. Seal rings 51 about the lands seal the piston against leakage from opposite ends of the piston chamber to an annulus or channel 52 defined between the lands. The annulus is at all times in communication with vent ports 53 which open through the side wall of the cylinder regardless of the axially moved position of the piston in its chamber.

The inner diameter wall of the piston is characterized by means of a forward annular surface 54 (FIGS. 2, 3) which bears upon the periphery of the sleeve as the piston reciprocates. Rearwardly of the surface 54, the inner diameter Wall of the piston enlarges conically at a slight angle to define a coned or tapered cam surface 55. The latter surface connects by means of a short beveled shoulder 56 with an end surface 57 of enlarged diameter. During reciprocation of the piston, the several surfaces of 4 the inner diameter of the piston are cooperable with a ring of balls 58, one of which is shown in FIGS. 2 and 3, in the sleeve 29 to effect a forward or a rearward movement of the sleeve along the chuck horn 14.

Each ball 58 is loosely disposed in a radial hole 59 of larger diameter in the periphery of the sleeve. The holes are spaced circumferentially equally apart. Here, there are eight such holes, of which one is shown in FIGS. 2 and 3. The radial depth of each hole is less than the diameter of the ball, so that a segmental portion of each ball projects into a continuous underlying groove 61 extending around the periphery of the chuck horn, and another segmental portion projects above the periphery of the sleeve 29. The balls at all times contact a forwardly inclined annular slope 62 of the groove as well as the back area of the 'ball holes 59. The sleeve has a forward or normal position, as in FIG. 2, to which it is normally biased by the load of the detent springs 36. The sleeve is limited in this forward position against endwise escape from the chuck horn by means of the balls 58. In this respect, the balls are held high upon the slope 62 in abutment with the internal surface area 57 and the beveled shoulder 56 of the piston by means of the backwall area 63 of the ball holes 59 under the bias of the detent springs 36.

When the piston is pneumatically moved rearwardly or to the left to the FIG. 3 position, the beveled shoulder 56 and the cam surface 55 successively ride over the balls to roll them slightly down the slode 62. In this action, the balls abut the back area 63 of the ball holes 59 and force the sleeve axially rearward to its gripping position, as in FIG. 3, against the resistance of the detent springs. As the piston moves rearwardly in this action, the low end of the cam surface 55 finally rides over the balls to wedge them between it and the slope 62. The wedged condition of the balls will lock the sleeve in its rearward position against the opposed force of the detent springs. It will remain in this wedged condition until it is released by a forward or return movement of the piston.

When the piston is pneumatically moved forwardly to the FIG. 2 normal position, the wedged condition of the balls is released as the high portion of the cam surface 55 and eventually the enlarged diameter surface 57 ride forwardly over the balls. Simultaneously with the forward movement of the piston, the detent springs re-expand to return the sleeve to its forward FIG. 2 position. As the sleeve is moved forwardly, the back wall areas 63 of the holes 59 roll the balls up the slope 62 into abutment with the beveled shoulder 56 and the enlarged diameter surface 57.

It is while the sleeve is in its forward FIG. 2 position, that the nosepiece 22 may be adjusted axially as needed relative to the collet, or removed free of the sleeve 29 to permit insertion or replacement of the collet. To remove the noscpiece for replacement of the collet, the sleeve is rotated until the nosepiece travels axially free of the sleeve.

A pneumatically operable air distribution or sequence valve unit 64 (FIG. 8) incorporated in a bore 65 of the body of piston 38 is selectively operable to cause live air flow from a connected external source to one or the other ends of the piston chamber 39. The valve unit includes a pair of stationary open-ended cam members 66 and 67 (FIGS. 8, 9, 12) between which a porting valve 68 (FIGS. 8, 15) is axially reciprocable. As the valve is reciprocated from one position to another, it cooperates with one or the other of the cam members whereby the valve is caused to be indexed angularly a distance of 45 from its last position. In this action, air feed and exhaust ports are caused to be brought alternately into register with ports leading to one or the other ends of the piston chamber or are caused to be shut off from both ends of the piston chamber, as will soon be described herein.

The cam member 66 (FIGS. 8-11) shown at the left in FIG. 8, is formed with a radial shoulder 69 around its periphery which is held seated upon an annular shoulder 71 defined by an enlargement of the left end of the valve bore 65. A plug 72, threadedly engaged in the end of the bore 65 so as to abut the cam member, seals the left end of the bore and holds the cam member rigidly against the shoulder. A cylindrical reduced body portion 73 of the left cam projects axially into the bore 65. The body 73 of the cam is defined by means of a succession of axially extending cam fingers 74, here four in number, spaced circumferentially equally apart. Each finger comprises an axially extending straight side 75, from the extremity of which a cam surface 76 declines counterclockwise to a point separated by a narrow space 77 from the straight side 75 of the next finger.

The right cam member 67 (FIGS. 8, 12-14) is of similar form except that the cam surfaces 78 of its fingers 79 decline in an opposite or clockwise direction. The peripheral radial shoulder 80 of the right cam is rigidly held seated upon a shoulder 81 (clearly shown in FIG. of an enlargement at the right end of bore 65 by means of a plug 82 (FIG. 8) threadedly engaged in and sealing the right end of the bore.

The porting valve 68 (FIGS. 8, -18) has a cylindrical body that is slidable axially in the bore 65 between the cam members. The ends of the body are defined by

cam fingers

83 and 84 which respectively complement the

fingers

74 and 79 of the left and right cam members. A compression spring 85 seated at one end against the right closure plug 82 and extending through the interior of the right cam member into an axial recess 90 of the valve biases the latter to a normal or returned position (FIG. 8) wherein its cam fingers 83 are engaged with those 74 of the left cam member. Valve 68 has a pneumatically actuated position (not shown) wherein the fingers 84 at its right end are similarly engaged with those 79 of the right cam member. A pilot pin 86, fixed in the right plug, projects axially into the spring 85 to guide the spring and limit radial movement of the spring caused by centrifugal forces. The inner diameter faces of the fingers 84 of the right cam are axially extended as at 88 beyond the extremities of the fingers to further guide and limit radial movement of the spring.

The right cam member has an angularly advanced position relative to the left cam member 66 so that its fingers 79 are positioned 45 out of phase from those 74 of the left cam member. In this arrangement, when the valve 68 is in its normal or left position, the crests of the fingers 84 at its right end are opposite the mid-points of the cam surfaces 78 of the fingers 79 of the right cam member. By means of this arrangement, each time the valve is moved from engagement with one cam member into axial engagement with the other, it will be cammed and rotatively indexed 45 in a clockwise direction.

This indexing feature permits selective porting of the valve with opposite ends of the piston chamber. To this end, the valve has a pair of inlet or feed ports 89 (FIGS. 8, 18) opening out of its surface at diametrically opposite points. These ports are in communication through the body of the valve with an inlet recess 91 at the left end of the valve. The recess connects, as appears in FIG. 8, through the interior of the left cam member and ports 92 in the cam shoulder with a surrounding air inlet annulus 93. The valve also has a pair of exhaust ports 94 (FIG. 17) opening out of its surface at diametrically opposite points. These ports communicate through the body of the valve with the recess 90 at the front end of the valve. The recess 90 communicates the interior of the valve with ports 95 leading through the shoulder of the right cam member to a surrounding exhaust annulus 96. The latter connects by a passage 97 through the body of the piston with the vent annulus 52. The

several ports

89 and 94 lie in a common plane perpendicular to the axis of the valve and are spaced circumferentially 90 apart. The bore 65 in which the valve operates is connected with the left end of the piston chamber (FIGS. 4, 5, 7, 8) by means of a pair of diametrically opposed ports 98 extending through the piston body; and is connected with the right end of the piston chamber (FIGS. 4, 5, 6, 8) by means of a second pair of diametrically opposed ports 99 extending through the piston body. The

several ports

98 and 99 lie in a common plane perpendicular to the axis of the valve, and are spaced 90 apart. In the normal condition of the valve as in FIG. 8, the

ports

89 and 94 of the valve are not only out of register with the

ports

98 and 99, but also are angularly disposed 45 out of phase with the latter ports. Each time the valve is shifted to the right in engagement with the right cam, it is indexed 45 clockwise, and two of the four

ports

89, 94 are brought into register with the ports 98 leading to the left side of the piston chamber, and two are brought into register with the ports 99 leading to the right side of the piston chamber, as will soon be further described.

The inlet annulus 93 to the valve is conected with an external source S of operating pressure air. In this respect, a feed line 101 (FIG. 2) extending through the interior of the lathe spindle 11 connects the air source with a single passage air swivel joint 102. The swivel joint is of a conventional type. It is connected with a passage 103 leading through an adapter 104 screwed in the left end of the chuck body. The passage 103 extending through the adapter connects with a passage 105 leading through the chuck body into the interior of a tube 106. The tube is fixed in the chuck "body and has an open end which projects with a slide fit partway into an axial bore 107 in the piston body. The forward end of this bore 107 communicates by means of a passage 108 (FIG. 5 through the piston body with the inlet annulus 93 (FIGS. 5, 8) of the valve.

Assuming that the chuck is in its normal condition, as in FIG. 2, in which the condition of the collet 16 is relaxed relative to the workpiece, the operation of the air chuck is as follows:

A main three-way supply valve 109 in the supply line 101 is turned from closed to open condition. Live air then flows through the connecting passages, described above, to the inlet annulus 93 of the valve bore from where it passes through the left cam 66 into the valve inlet recess 91 to shift the valve 68 to the right into camming engagement with the right cam 67. In this action, valve 68 is cammed and indexed clockwise 45 to register its two feed ports 89 with the two ports 99 leading to the right end of the piston chamber, and to register its two vent ports 94 with the two ports 98 leading to the left end of the piston chamber 39. Accordingly, the piston is forced to the left to the FIG. 3 position; and air trapped at the left end of the piston chamber is vented through the valve body and connecting passages to the annulus 52 about the piston leading to the vent ports 53. Left or rearward movement of the piston forces the sleeve 29 and nosepiece 22 axially rearward, as earlier explained, to contract the collet 16 into gripping relation with the workpiece 21.

Subsequent to the rearward or leftward movement of the piston, the supply valve 109 is manipulated to its vent position so as to allow air trapped at the left end of the indexing valve 68 to be vented. The valve return spring then relaxes to shift the valve 68 back to its normal condition in engagement with the left cam, as in FIG. 8. The return movement of valve 68 in cooperation with the left cam 66 carries the

valve ports

89, 94 out of register from the

ports

95, 98, and indexes the valve 45 further clockwise preparatory to subsequent shifting of the valve to the right. Returning the sequence valve to its normal position at the left does not affect the position of the piston. The piston remains in its moved condition until pneumatically re-shifted to the right. Further, the cammed condition of the piston relative to the balls 58 insures the gripping relation of the chuck with the workpiece during operation of the spindle.

To move the piston back to its normal position at the right so as to free the collet from its gripping relation with the workpiece, the main valve 109 is again manipulated to open condition. Live air then flowing through the left cam 66 to the rear recess 91 of the valve shifts the valve to the right as before and indexes it a further 45 clockwise causing the two feed ports 89 of the valve to be registered this time with the ports 98 leading to the left end of the piston chamber, and the vent ports 94 to be registered with the ports 99 leading to the right end of the piston chamber. Accordingly, the right end of the piston chamber is vented and the piston is simultaneously moved to the right to its normal condition. Manipulating the main valve 109 to vent condition again causes simultaneous return of the sequence valve 68 to the left normal position and indexing thereof clockwise a further 45.

It is to be noted that the sequence valve permits the chuck to be used with a single three-way main valve 109 and a single air supply line 101 to the chuck in association with a driving spindle 11 and a single passage swivel joint 102. The single passage swivel joint is relatively small in structure and can be accommodated within the interior of the driving spindle.

What is claimed is:

1. An air chuck comprising a chuck body adapted for attachment to a driving spindle, a collet actuating unit slidable along the chuck body to and from a collet actuated condition, spring means biasing the unit to a normal collet released condition, a piston chamber about the unit, a single piston pneumatically operable in the chamber having cooperation with the unit when the piston is moved in one direction to slide the unit to a collet actuated condition against the bias of the spring means, the spring means adapted when the piston is moved in the opposite direction to return the unit to its collet released condition, valve means incorporated in the body of the piston for distributing piston operating air alternately to opposite ends of the piston chamber, supply air control means for selectively causing supply air flow to the distributing means, and a single passage swivel joint connecting the control means with the valve means.

2. An air chuck as in claim 1, wherein the single passage swivel joint has a single feed line connection with the supply air control means.

3. An air chuck as in claim 1, wherein the collet actuating unit carries circumferentially of its surface a succession of rollers, and the piston has an interior annular cam surface which is cooperable with the rollers as the piston is moved in said one direction to cam the unit to its collet actuated condition.

4. An air chuck as in claim 1, wherein the valve means includes a valve chamber having first ports leading through the piston to one end of the piston chamber and second ports leading through the piston to the opposite end of the piston chamber, and a distributing valve is selectively slidable in the valve chamber for communicating the first and second ports alternately with the supply air control means.

5. An air chuck as in claim 4, wherein means is provided for pneumatically causing movement of the distributing valve axially in one direction, and spring means is provided for returning it in the opposite direction.

6. An air chuck as in claim 1, wherein the valve means includes a valve chamber having first ports connected with one end of the piston chamber and second ports connected with the opposite end of the piston chamber, a distributing valve is slidable in the valve chamber having inlet ports communicating with the supply air control means and having exhaust ports communicating with atmosphere, the distributing valve having a first axially moved position in which the inlet ports register with the first ports and the exhaust ports register with the second ports, the distributing valve having a further axially moved position in which the inlet ports register with the second ports and the exhaust ports register with the first ports, and having a normal position in which the inlet and exhaust ports are not registered with either the first or the second ports.

7. An air chuck as in claim 1, wherein the valve means includes a valve chamber having first ports leading through the piston to one end of the piston chamber and second ports leading through the piston to the opposite end of the piston chamber, a distributing slide valve having axial and angular movement in the valve chamber, the valve including inlet ports connected with the supply air control means and including exhaust ports connected with atmosphere, the valve having a normal position in which its inlet and exhaust ports are out of register with and advanced angularly out of phase from the first and second ports, the valve having an axially moved and angularly advanced position from its normal position in which the inlet and exhaust ports are respectively registered with the first and second ports, and the valve having a subsequent axially moved and further angularly advanced position from its normal position in which the inlet and exhaust ports are respectively registered with the second and first ports.

8. An air chuck as in claim 7, wherein the valve is pneumatically movable from its normal position, and a spring is arranged to subsequently return the valve to its normal position.

9. An air chuck as in claim 7, wherein cam means is arranged at each end of the valve chamber, the valve has cam means at one end which is cooperable with the cam means at a corresponding end of the valve chamber to cause the valve to be indexed angularly a predetermined degree each time the valve is moved axially from its normal position, and the valve has cam means at its opposite end which is cooperable with the cam means at the corresponding end of the valve chamber to cause the valve to be indexed angularly a predetermined degree each time the valve is returned to its normal position.

10. In an air chuck including a rotary chuck body, work holding means, a piston chamber, and a pneumatically operable piston selectively movable in the chamber to cause a work gripping or a work released condition of the holding means, the piston and holding means arranged to be carried about together with the chuck body, a live air inlet passage extending through the chuck body into the body of the piston, separate passages in the piston communicating through the piston with opposite ends of the piston chamber, slide valve means incorporated in the body of the piston which is selectively operable to communicate the inlet passage alternately with the separate passages, a live air supply line, and a single passage swivel joint connecting the supply line with the inlet passage.

References Cited UNITED STATES PATENTS 2,500,383 3/1950 Sadler 2794 2,582,680 1/1952 Church 279-4 3,451,314 6/1969 Smrekar 279-4 LESTER M. SWINGLE, Primary Examiner D. D. EVENSON, Assistant Examiner