US1987862A - Method of and hydraulic press for inserting bushings - Google Patents

Description

E. K. MORGAN Jam 15, 1935.

METHOD OF AND HYDRAULIC PRESS FOR INSERTING BUSHINGS Filed April 28, 1952 5 Sheets-Sheet l O w w /w 0 M O O M m 3 I WM H O n W H UNI Z 0 Fl H| l HH h l I l O H. G IIIIIIII, M O O F C Lllfil T n 1 1 Jan. 15, 1935. E. K. MORGAN METHOD OF AND HYDRAULIC PRESS FOR INSERTING BUSHINGS Filed April 28, 1952 5 Sheets-Sheet 2 Jan. 15, 1935. E. K. MORGAN 1,987,862

METHOD OF AND HYDRAULIC PRESS FOR INSERTING BUSHINGS Filed April 28, 1932 5 Sheets-Sheet 5 ,F za Liiiiii'ffffi:If @00000 00mm? iim H llllil Jan. 15, 1935. E. K. MORGAN METHOD OF AND HYDRAULIC PRESS FOR INSERTING BUSHINGS Filed April 28, 1932 5 Sheets-Sheet 4 Jan. 15,1935. E. K. MORGAN 1,987,862

METHOD OF AND HYDRAULIC PRESS FOR INSERTING BUSHINGS Filed April 28, 1932 5 Sheets-Sheet 5 Patented Jan. 15, 1935 METHOD OF AND HYDRAULIC PRESS FOR INSEBTING BUSHINGS Everette K. Morgan, Rockford, Ill., assignor to The Ingersoll Milling Machine 11]., a corporation of Illinois 00., Rockford,

Application April 28, 1932, Serial No. 608,040

19 Claims.

This invention relates to a novel method of and an hydraulic press for inserting bushings,

such, for example, as the valve guide bushings in internal combustion engines.

The insertion of valve guide bushings with the correct press fit is highly important for the reason that a loose bushing will usually work upwardly, sometimes to such an extent as to actually hold a valve open. Even where the bushing does not move that far, its movement out of position destroys its further use as a pilot for the end of the valve spring, so that the spring can work sidewise and make the valve stem bind and cause faulty engine performance. operated at high speeds, as in thecase of airplanes and automobiles, are found to be particularly subject to troubles arising from loose valve bushings, and many air casualties are directly traceable to such engine troubles. With the old methods employed for inserting bushings, and either testing their fit after insertion by tapping the same with a hammer, or relying on the judgment of the workman as to whether the same is tight enough. simply by noting whether the bushing can be driven home easily or not,,there was manifestly no real certainty as to the correct press fit of bushings in an engine block. It is, therefore, the principal object of my invention to insert bushings according to a new method in which each bushing is inserted by means of a plunger carried in a head and subjected to a given yielding pressure, whereby in the movement of a workcarrying platen toward the head to detect the loose fit of bushings by their failure to overcome the yielding pressure and produce backup movement of the plungers in the head in the stroke of the platen. With this method it is manifestly possible to insert the entire set of bushings in a block, or at least a plurality of bushings simultaneously, and the loose bushing or bushings are indicated in the manner stated and marked for replacement.

It is another important object of my-invention to provide an improved hydraulic press adapted for inserting bushings in accordance with the above method. ,A special feature of this press is the provision of a retractible stop for limiting the initial movement of the platen so that loose bushings can be marked before final movement of the platen to press all of the bushings home. This makes it possible to operate on shoulder type bushings which wouldotherwise .be diiflcult to handle, because of the fact that their movement is limited by the shoulder. Plain bushings'do not require special handling because a loose bush- Engines ing of that type will be pressed an appreciable distance beyond its working point so that it is apparent at a glance that its fit is not sufllciently close to the set standard.

Still another object consists in the provision of signals or telltales for automatically indicating the loose bushings, whereby to avoid any guesswork.

The invention embraces other objects and advantages which will appear in the course of the following detailed description, in which reference is made to the accompanying drawings, wherein-- Figure 1 is a front view of a press made in accordance with my invention;

Fig. 2 is a fragmentary side view partly in vertical section showing the pedal-operated valve controlling the operation of the platen;

Fig. 3 is an enlarged vertical sectional detail illustrating the operation of the machine in the insertion of a bushing having the correct press fit;

Fig. 4 is a similar view illustrating the operation in the case of a loose bushing;

' Figs. 5 and 6 are-views corresponding to Figs. 3 and 4 but showing the operation upon plain bushings as distinguished from the shouldered bushings appearing in the other views;

Fig. 7 is an enlarged view of a portion of the head of the machine partly in front elevation and partly in vertical section .to show how the loose bushings in a set are indicated so as to single them out from the others; p Fig. 8 is a horizontal section on the line 8-8 of Figure 1 mainly to show the retractible stop and the operating means therefor;

Fig. 9 is a vertical sectional detail on the line 9,9 of Fig. 7 to further illustrate the stop;

Fig. 10 is a horizontal section on the line 10-10 of Figure 1 showing the engine block in plan and illustrating part of the block locating means and electric circuit control;

' Fig. 11 is a plan view of the dowel pin operating means;

Fig. 12 is a sectional detail on the line 12-42 of Fig. 10 illustrating the operation of the dowels;

Fig. 13 is a view on the line 13-43 of Fig. 10 illustrating the electrical control provided in connection with the dowel operating means, and

Fig. 14 is an oil and electrical circuit diagram for the press.

Similar reference numerals are applied to corresponding parts throughout the views.

While the present invention has particular reference to the insertion of shouldered valve guide bushings 10 or plain valve guide bushings 10 in internal combustion engineblocks 11, it will soon be apparent that the invention is not limited to this special work but is adapted for the insertion of any kind of bushings, or for that matter any parts which it is important be inserted with the correct press fit. The operation herein illustrated and described should, therefore, be taken as merely one example of many possible applications of the invention. Furthermore, while I have illustrated the use of a hydraulic medium, or, more specifically, the combination of an hydraulic and a pneumatic medium to afford only a predetermined pressure on the plungers for inserting the bushings and allowing the plungers to back up when the pressure thereon is overcome as a result of the tight fit of the bushing, it will also be apparent that a similar result would be obtained by means of suitable springs. In other words, it is only essential that the plungers be yieldable at a predetermined pressure, and any means suitable for accomplishing that purpose comes properly within the purview of my invention.

Referring now principally to Figure 1, the numeral 12 is applied to the base of the press which has side columns 13 supporting a horizontal head or cross rail 14. Guides 15 on the columns 13 have a work carrying platen or table 16 slidable thereon for vertical movement toward and away from the head. A plunger 17 extends downwardly from the platen into the working cylinder 18 in the base for movement with the double-acting piston 19 operating in the cylinder. 20 is an apron depending from the platen simply to enclose the upper end of the cylinder and the plunger, for the sake of appearance. The head 14 carries plungers 21 on which holders 22 are provided for the valve guide bushings 10 or 10', as the case may be. The holders 22 are stems made to fit snugly in the bushings and having any suitable means for frictionally gripping the same. In the present case the lower ends of the -stems are shown as split and slightly spread to provide the desired frictional hold on the bushings. From this much description it will be seen that a set of bushings can be placed on the holders 22 in alignment with the suitably reamed holes 23 provided therefor in the engine block 11, and then inserted by an upward movement of the platen 16 under hydraulic pressure applied to the piston 19. The holders 22 in the return of the platen will, of course, slip out of the bushings, leaving them in place in the block. The holes 23 are, of course, all reamed at one time in a multiple spindle machine. There is, however, a certain amount of variation in the size of these holes due to the difiference in the reamers. On the other hand, the bushings to be inserted in these holes are all machined within a certain tolerance. Naturally, then, a medium sized bushing when entered in a medium sized hole will have the correct press fit, but a small sized bushing, that is, one below medium size, will undoubtedly be too loose if entered in a hole above medium size. There is no objection to bushings having something above a correct press fit, but there is a decided objection to a bushing having anything below a correct press fit, as indicated above. The purpose of the present invention, as will soon appear, is to indicate which bushings are loose, that is to say, arebelow a correct press fit.

Referring to Figs. 1, 2. '7 and 14, it will be seen that oil is delivered to the lower end of the cylinder 18 through a pipe 24 from a pump by shifting the valve 26 by means of a foot pedal 27. A compression spring 28 cooperates with one end of the valve to normally hold it in the position illustrated in Fig. 2, in which the delivery is through the pipe 29 to the upper end of the cylinder 18 to return the platen 16 to the lowermost position. In other words, the depression of the pedal 27 takes care of the raising of the platen, and it is only necessary to release the pedal to secure the return of the platen. The pump 25 is continuously operated by means of the electric motor 30 so long as the press is in use.

As best appears in Figs. 3-7, the head 14 is cored out to provide an oil pressure chamber 31 and an air chamber or accumulator. 32 to afford a place for the oil to back up when the plungers 21 back up in the head against the pressure of the oil in the chamber 31, due to the resistance to movement of the bushings into their holes, as will soon appear. The oil in the chamber 31 is maintained at a predetermined pressure by communication with the pump 25 through the line 33 and check valve 34 (see Fig. 14). The plungers 21 project through stuifing boxes 35 into the chamber 31 and, hence, are normally urged outwardly under the pressure of the oil in said chamber. Outward movement, however, is prevented by reason of stems 36 extending upwardly from the plungers 21 through holes 37 in the top wall of the chamber 31 and having nuts 38 threaded on the projecting ends thereof for abutment with said wall. Any other suitable means could be provided for holding the plungers against outward movement. A chamber 31 has the stems 36 projecting into it and any leakage past the stems from the chamber 31 is conducted from the chamber 31' through a pipe 39 back to the sump of the pump 25. Nuts 40 are threaded on the plungers 21 outside the chamber 31 in a predetermined spaced relation to the gland nuts 41 on the stuifing boxes. This is to limit the inward movement of the plungers when the bushings have the correct press fit in their holes and accordingly overcome the pressure of the liquid in the chamber 31. The nuts 40 in the case of a plain bushing, like the bushings 10' shown in Figs. 5 and 6, are set so as to allow a predetermined backing up of the plungers under resistance of the bushings, so that when the platen 16 is given a predetermined stroke, the bushings which have the proper press fit will be inserted to the correct distance, as shown in Fig. 5, whereas those bushings which are so loose that they do not afiord sufiicient resistance to cause the plungers to back up in the manner stated will be inserted to an abnormal distance. Naturally, if the setting of the nuts 40 is made for enough movement of the plungers 21, the loose bushings can be indicated simply by the extent to which they will project below the line of bushings that have the correct press fit. However, I prefer to provide some definite means for indicating those bushings which because of their loose fit, should 'be replaced. A signal or telltale means for this purpose is indicated generally by the reference numeral 42. It consists of an elongated housing 43 suitably provided on the head 14 in front of the row of plungers 21 and having electric lights 44 mounted therein behind windows 45. Switches 46 in the housing are normally held closed by compression springs 47 to complete electric circuits through the lights, as indicated in Fig. 4.

Small push rods 48 project from the back of the housing 43 toward the plungers 21 for operation thereof by means of cam-shaped projections 49 provided on the plungers. The projections 49 are so located with respect to the push rods 48 to leave the switches 46 closed so long as the plungers 21 have not been backed up by the bushings associated therewith. Thus, in Fig. 5 it will be observed that the cam-shaped projection 49 has depressed the push rod 48 so that there is no light appearing at the window 45. This indicates there is nothing wrong with the fit of this particular bushing, but in Fig. 6 it will be noticed that the projection 49 has not depressed the push rod 48 in the up-stroke of the platen 16, owing to the fact that the plunger 21 was not backed up against the pressure of the liquid in the chamber 31 by the bushing, the latter not having the correct press fit. Consequently, the light appears at the window and indicates the necessity for replacement of this particular bushing. I make reference only to Figs. 5 and 6 at this point because of the fact that a two-stage operation is used in the case of the shouldered bushings illustrated in Figs. 3 and 4, which requires some further explanation. It will suflice at this point to state that at the commencement of the up-stroke of the platen 16, all of the windows 45 will be illuminated since all of the switches 46 are closed at that time. If any one of the lights is defective, it is immediately apparent to the operator and given attention so that he can rely later upon the lights for indication of the loose bushings requiring replacement. Near the end of the up-stroke the plungers operating on loose bushings will have their cam projections ride over the push rods 48 thus momentarilyputting out the lights associated with the loose bushings, and at the end of the stroke of the platen the cam projection 49 on those plungers operating on bushings having the correct press fit will depress the push rods associated therewith and, consequently, the only lights that will appear will be those associated with the plungers operating on loose bushings.

The shouldered bushings require a two-stage operation, in the first stage of which an indication will be given of the loose bushings, and in the second stage of which the bushings will be set home. This operation is secured by providing stops 50 projecting downwardly from the head 14 for engagement with the cylinder block, as illustrated in Figs. 7 and 9. The stops are of plunger form having enlarged upper ends 51 received in bores 52 in the head and retained by bushings 53 fitting about the same below the en-, larged ends. Nuts 54 are threaded on the projecting ends of the plungers and fixed in adjusted position by set screws 55, whereby to limit upward movement of the plungers. Retractible stop members 56 are provided, which, in their op-. erative position, serve to hold the stops 50 extended, as shown in Fig. 9, with the nuts 54 in a predetermined spaced relation to the bottom of the head. The members 56 are notched out, as at 57, so that when they are moved to retracted position with these notches in register withgthe plungers the latter are free to back into their bores far enough for the nuts 54 to limit their movement (see Fig. 5). The bottoms of the notches are inclined and the upper ends of the plungers are correspondingly inclined, as indicated at 58, to permit movement of the members 56 to operative position, that is, from the retracted position shown in Fig. 5 to that shown in Fig. 9, by the turning of pinions 59 meshing with rack teeth 60 formed in the members 56. The pinions 59 are mounted on a shaft 61 received in suitable bearings 62 on the head 14 and having a central operating pinion 63 mounted thereon at the middle thereof. A rack 64 meshes with the pinion 63 and is operated by a piston 65 in a cylinder 66 mounted-on the bottom of the head 14 at the back thereof (see Fig. 3). Oil under pressure is delivered toeither end of the cylinder 66 from the pump 25 by operation of a pilot valve 67, which is suitably mounted on the side of the press, as shown in Figure 1. A hand lever 68 is shown for operating the valve and, while I have not disclosed any means for holding the lever 68 normally in one position to keep the stop members 56 in operative position, it should be understood that it would not require anything more than a spring urging the lever to move in one,

direction against a stop to secure that result. However, since the press will be used interchangeably for operation on plain bushings or shouldered bushings, I prefer to leave the operation of the valve 67 entirely up to the operator, to be moved selectively to either position. In Fig. 14, it is clear that the pipe 69 delivers oil under pressure to the valve 67 from the pump 25 and if the valve is moved from a neutral position to the position shown, oil is delivered in front of the piston 65 to move the same to the position illustrated, whereby to hold thestop members 56 in operative position. Oil from behind the piston is drained to the sump of the pump 25 through pipe 70. When the stop members 56 are to be retracted the valve 67 is moved the other way from neutral position so as to' deliver oil from the pipe 69 behind the piston 65, the oil from in front of the piston being then drained through the pipe '71 to the sump. In operation, assuming that the valve 6'7 is in the position shown in Fig. 14, holding the member 56 in operative position, it is clear that the upward movement of the platen 16 with the engine block 11 will be limited, as indicated in Fig. 9. At this time, the loose bushings are indicated, as shown in Figs. 4 and "I, by means of the lights at the windows associated therewith, all of the other windows associated .with the bushings having the proper press fit being unlighted, as indicated in Figs. 3 and '7. The operator will, therefore, simply mark-the loose bushings requiring replacement. Then, without releasing foot pressure on the pedal 27, the operator will simply move the lever 68 to its opposite limit whereby to retract the stop members 56. and allow further upward movement of the block 11 with the platens 16 to set all of the bushings home, the loose ones along with the tight ones. Afterward, when the block 11 is removed from the press the marked bushings are driven out and bushings of the proper size to fit the holes are entered.

Referring now to Figures 1 and 10-14, it will be observed that the engine block 11 is arranged to be located accurately on the platen 16 by means of a plurality of dowels 72. Two are sufiicient, although I have illustrated four, one at each corner. It is, of course, important to have the block accurately located because it would make it necessary to replace the spindles or plungers 21 if the platen 16 were raised with an engine block improperly positioned thereon. The dowels are guided through accurately ground bushings 73 in accurately located bores 74 provided there- Y LU for in the platen 16. Rack teeth 75 are formed beveled gears'80 on a transverse shaft 81 arranged to be turned by means of a hand lever 82. It is,

I therefore, clear that all of the dowel pins 72 are raised or lowered simultaneously by operation of the lever 82, the pins being raised by clockwise movement of the lever and lowered by counterclockwise movement (see Fig. 11) Now, in order to insure, first of all, that a block 11 has been placed on the platen, and secondly, that the dowel pins 72 have been raised to properly locate the block, before the pedal 2'? is depressed to raise the platen, I have provided two control switches 83 and 84 connected in series with a solenoid 85. The solenoid 85 has an armature 86 which, so long as the solenoid is not energized, is disposed in its lowermost position in the path of a lever 87 arranged to be operated by the pedal 2'7 to shift the valve 26, whereby to prevent such operation. The switch 83 is normally held open by a spring 83 and has a plunger 89 projecting therefrom for engagement by a portion of the block when the latter is placed on the platen 16 in abutment with stops 90, which are provided to roughly position the block. In this way, the switch 83 is closed when the block is placed on the platen in approximately the right position. The switch 84 likewise has a spring 91 normally holding the same in open circuit position, and a plunger 92 projects from the switch in the path of movement of an adjustable set screw 93 provided on a lug 94 formed on the hub of the lever 82, as clearly appears in Fig. 13, so that the switch is arranged to be closed when the lever 82 is moved in a clockwise direction from a substantially horizontal position to a substantially vertical, limit position. In that way, the circuit iscompleted through the two switches 83 and 84 to energize the solenoid85 and raise the armature 86 to retracted position with respect to the lever 87, so that the pedal 27 can be depressed. The spindles of the press are, therefore, fully protected against jamming.

The pump is known as the Oilgear QW pump which is no doubt covered in a copending application filed by The Oilgear 00., Milwaukee, Wisconsin. It will, therefore, sufiice for the present purposes to state that the same comprises a gear pump section 95 and a piston pump section 96, preferably inside a single housing. The piston pump in the QW pump happens to be what is known as a self-centering pump because of its being arranged to build up to a predetermined pressure in the line and then automatically shift to a position of little or no delivery, whereby to merely maintain the predetermined pressure and no more. However, that phase of the piston pump is of no special significance so far as the present invention is concerned, and the circuit diagram has not been complicated by a showing of that feature; so far as the present operation is concerned the piston pump need not be selfcentering, because a blow-off valve could be provided to open at the predetermined pressure so as to by-pass excess oil to the sump. The sump is indicated at 9'7. 98 indicates a suction line leading from the sump to the gear pump 95, and it will be observed that the gear pump primes the piston pump by delivery thereto from the discharge line 99. The piston pump discharges through a line 100 communicating with the pressure port 101 of the valve 26. The valve 26 determines by its position whether the oil is delivered to the line 24 or the line 29. Assuming that the valve 26 is in the position shown in Fig. 14, the delivery is to the line 29 to the upper end of the cylinder 18 to lower the platen by means of piston 19. The oil below the piston is drained through line 24 back to the valve, and from there through line 102 leading back to the discharge side of the gear pump so as to be delivered to the intake of the piston pump, or, if there is an excess of oil, to be returned to the sump through the line 103 and a low pressure relief or footvalve 104. The latter offers sufiicient back pressure on the piston to insure smooth operation. When the piston 19 has moved as far as it will go, pressure in the line 100 builds up until it overcomes the high pressure relief valve 105 which then allows drainage to the sump through the line 106. On the up-stroke of the piston 19, when the valve 26 delivers oil from the pressure port 101 to the line 24, the foot valve 104 offers suiiicient back pressure on the piston 19 in the drainage of oil from above the piston to insure smooth operation. The valve 26 is shown in position for delivering oil to the upper end of the cylinder 18 so as to keep the platen in lowered position, that being the normal position of the valve secured by action of the spring 28.

It is believed the foregoing description conveys a good understanding of the objects and advantages of my invention. The appended claims have been drawn to cover all legitimate modifications and adaptations.

The mechanism herein disclosed for insuring proper positioning of the work piece prior to operation of the tools therefrom forms the subject matter of a copending divisional application Serial No. 668,519, filed April 29, 1933.

vI claim:

1. The method herein descibed which consists in entering parts in holes wherein they are to I have a press fit. then testing the parts for the correctpress fit by determining whether it takes at least a predetermined minimum pressure to move them in the holes, and then pressing the parts into the holes, so that the parts having more than a minimum fit are moved a predetermined distance in the holes, and so that those parts having less than a minimum fit are moved a different distance in the holes to give a loose fit indication.

' 2. The method herein described which consists in entering a part in a hole wherein it is to have a press fit, testing it for the correct fit by starting it into the hole with a pressure member adapted to yield when anything above a predetermined pressure is exerted thereon, and then pressing it farther in the hole the full distance desired.

3. The method herein described for press fitting parts and detecting faulty fit of any one or more of a plurality of parts adapted to have a press fit in holes therefor, which consists in entering the parts simultaneously in the holes therefor, then simultaneously pressing the parts a certain distance into the holes but by partially independent operation upon each testing all of the parts for correct press fit by determining whether it takes more than a predetermined min- .imum pressure to move each individual part in the hole therefor.

4. The method herein disclosed for detecting faulty fit of any one or more of a plurality of parts adapted to have a press fit in holes therefor, which consists in entering all of the parts simultaneously in the holes therefor, and simultaneously testing the parts for correct press fit by pressing the same into the holes with members each adapted to yield when anything above a predetermined pressure is exerted thereon, and then pressing the parts into the holes.

5. The method of inserting press fit parts such as bushings into holes which consists in simultaneously entering a plurality of such parts into the holes therefor, andpressing the parts into place with members each adapted to indicate individually the part, which presses into place with less than a predetermined pressure applied.

6. The method of inserting press fit parts such as bushings so as to detect those'liaving a loose fit, which consists in pressing the parts into their holes with members yieldable when more than a predetermined thrust .is exerted thereon, whereby to indicate less than a minimum fit of any part or parts which fail to cause the members associated therewith to yield.

7. The method herein described which consists in entering parts in holes wherein they are to have a press fit and wherein they are to be entered normally a certain distance, testing the parts for the correct press fit before pressing the same in the full distance, by pressing the parts into the holes only partway and in such a manner as to indicate whether it takes more than a predetermined minimum pressure to move them in the holes, then suitably marking for subsequent removal the parts which give a loose fit indication, and finally pressing all of theparts into the holes to a predetermined point.

8. A machine of the class described comprising a work support, a tool support, one of said supports being movable toward and away from the other, a plurality of holders on the tool support for maintaining in alignment parts to be entered with a press fit in holes in the work, means yieldably supporting the holders in a predetermined position on the tool support, the same permitting a predetermined amount of retrograde movement of the holders individually when more than a predetermined thrust is exerted thereon, and means for positively moving the movable support.

9. A machine as set forth in claim 8 including means for indicating which holders have been given retrograde movement. I

10. A machine of the class described comprising a work support, a tool support, one of said supports being movable toward and away from the other, a plurality of holders on the tool support for maintaining in alignment parts to be entered with a press fit in holes in the work, plungers mounted for retrograde movement on the tool support with the holders, means yieldable at a predetermined pressure and serving to hold the plungers in a normal position with respect to the tool support, whereby to permit retrograde movement of the holders when more than a predetermined thrust is exerted thereon, and means for positively moving the movable support.

11. A machine as set forth in claim 10 including means on the tool support for indicating which of the plungers have been given retrograde movement. r

12. A machine of the class described comprising a work support, a tool support, one of said supports being movable toward and away from the other, a plurality of holders on the tool support for maintaining .in alignment parts to be en tered with a press fit in holes in the work, plungers slidably received in holes provided therefor on the tool support for retrograde movement with the holders, said tool support having a fluid pressure chamber provided therein communicating with said holes whereby to hold the plungers extended toa predetermined position under a predeter- -mined fiuid pressure, and means for positively the other, a work holder onthe tool support for.

holding in alignment 9, part to be entered with a press fit in a hole in the work, a plunger mounted on the tool support for retrograde movement with the work holder, means yieldable at a predetermined pressure for holding the plunger in extended relation to the tool support, means to positively limit the retrograde movement of said plunger, and means for positively moving the movable support.

16. In a=machine of the class described, the combination of a work support, a tool support, the one support being movable toward and away from the other, a holder on the tool support for holding in alignment a part to be entered with a press fit in a hole in the work, a plunger mounted on the tool support for retrograde movement with the holder, a chamber containing a pressure fluid medium on the tool support for holding the plunger in extended position relative to the tool support, whereby to permit retrograde movement when a predetermined thrust is exerted on the plunger, means for positively limiting the retrograde move-' ment of the plunger, and means for positively moving the movable support.

17. A machine as set forth in claim including means for indicating when the plunger is given retrograde movement.

18. A machine as set forth in claim 15, wherein the movement of the movable support is normally limited by engagement with a stop, the machine including a retractable stop member arranged to engage the stop, whereby to provide for less movement of said support when desired.

'19. A machine for inserting a part with a predetermined press fit into a hole in a work piece having, in combination, two members mountedfor relative movement toward and away from each other in the direction of the axis of said hole when the'work piece is mounted on one of the members, an abutment on the other member engageable with one end of the part to transmit pressure thereto for forcing the part into said hole in the movement of said members toward each other;

and means yieldable under a predeterminedpressure for holding said abutment against movement relative to its supporting member until said pressure has been overcome in the entry of the part insaid hole, yielding of said abutment during entry of thepart into the hole constituting an indication of the proper fit.

EVERE'I'I'E K. MORGAN.

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