US2049444A

US2049444A - Drilling machine

Info

Publication number: US2049444A
Application number: US652316A
Authority: US
Inventors: Eric J Hirvonen
Original assignee: Leland Gifford Co
Current assignee: Leland Gifford Co
Priority date: 1933-01-18
Filing date: 1933-01-18
Publication date: 1936-08-04
Anticipated expiration: 1953-08-04

Description

Aug. 4, 1936; E. J. HIRVONEN' DRILLING MACHINE 2 Sheets-Sheet l Invezzibr.

Filed Jan. 18, 1933 Aug. 4, 1936. -E. J. HIRVONEYN DRILLING MACHINE 2 Sheets-Sheet 2 17122621 Zor.

Filed Jan. 18, 1935 Qm w i E I IIII Patented Aug. 4, 1936 UNITED PATENT crates,

DRILLING MACHINE Application January 18, 1933, Serial No. 652,316

22 Claims.

This invention relates to machine tools'and especially to drilling machines wherein the cutter can exist in machines designed for the simultaneous drilling of lubricating or oil passages in the crank shafts of internal combustion engines,

with which type of machine this invention is particularly concerned. The crank shaft of an automobile engine, for instance, is quite commonly supplied with oil under pressure at the bearing portions thereof and the oil is conveyed through oil passages in the crank shaft from an intermediate bearing portion into the connecting rod portions, or throws, of the shaft on opposite sides of the bearing, the oil passages having a common opening at the surface of the bearing and separately extended at a divergent angle into and opening at the surface of a crank throw. If the oil passages are automatically drilled simultaneously it is possible for the two drills to come into contact with each other at or near the surface of the bearing portion of the shaft, thereby resulting in damage at least to the drills and possible damage to the crank shaft and to the drilling mechanisms.

An object of the present invention is the provision of a machine tool, as a crank shaft drilling machine, having two drilling mechanisms which advance the drills into the work along convergent lines and mechanisms for preventing interference between the cutters or drills.

The present invention embodies two of the drilling units described and claimed in my copendingapplication Serial No. 636,855, filed October 8, 1932, each unit having drill rotating means and hydraulic means to advance the drill automatically to successively advanced positions in the work with alternate retracting movements to an intermediate retracted position followed by a final retracting movement to a final fully retracted position where the mechanism is held against further advance of the drill until again restarted on another cycle of operations.

It is a further object of the present invention to provide a combination of two such units arranged to advance their respective drills along lines that converge, with hydraulic control mechanism so arranged that each unit can drill its full length of hole without interference between the drills of the units. I

Another object of the invention is the combination of two of the above described drilling units advances and holds the first unit against advance,

set to advance their respective drills along convergent lines and interference-preventing hydraulic control mechanism so arranged that the drill that arrives first in the interfering-position is permitted to continue to advance until it is retracted by its mechanism, while the drill of the other unit is prevented from advancing, the control mechanism being so arranged that when the unit that reaches interfering-position first and continues its advance retracts, the other unit if the mechanism associated therewith is so set as to require further advance thereof.

A further object is generally to improve the construction and operation of hydraulically actuated machine tools.

Fig. 1 is a plan view of a crank shaft drilling machine embodying the present invention.

Fig. 2 is a side elevation of the machine of Fig. 1.

Fig. 3 is an enlarged side elevation of one of the drill units of Fig. 1. v

Fig. 4 is a diagrammatic representation of the hydraulic control mechanism for the drill units.

Fig. 5 is a sectional view of a bearing portion of a crank shaft and illustrating the manner in which the drills are advanced into the shaft and the manner in which interference between the drills can take place.

The machine embodying the present invention includes a flat horizontal table It) on which the similar drill units A, B, and C, D, are supported in such manner that their angular relation with each other and their distance from the work can be changed as desired. The table is supported on a pedestal 12 which preferably is hollow and contains the hydraulic pump and other associated parts of the hydraulic system. The machine is herein illustrated as arranged to drill oil holes in a crank shaft M which is here shown as having the two end bearings l6 and the center bearing I8 with the crank throws and Hon opposite sides of the center bearing and the crank throws 24 adjacent the end bearings. The crank shaft herein illustrated is designed for a four cylinder or, it may be, an eight cylinder, V-type engine. The crank shaft is suitably supported on blocks 26 and is held releasably thereonby clamping levers 28 and the operating levers 30 therefor. Oil passages 32 are drilled from the middle of the bearing faces of the end bearings 16 through the crank shaft to the middle of the bearing faces of the end crank throws 24. Other oil passages 34 and 3B are drilled from the middle bearing faces of the middle crank throws 20 and 22 into the middle of the bearing face'of the center bearing 3, the

oil passages

34 and 36 being convergent and merging into one another at or near the face of the bearing 88.

The invention is particularly concerned with 60 larly concerned with an arrangement whereby each drill unit can operate independently of the other down to the interfering point and thereafter the units are under such control that interference is prevented. The drilling units A and B are or can be identical. Each is constructed preferably as described in my above referred to application, and hasmechanism for advancing the drill by successively increased distances into the work alternated with retracting movements to an intermediate retracted position where the drill clears the work and the chips can fall therefrom and terminated in a final retracting movement into a completely retracted position where the drill is held against further advance until restarted on a second cycle.

The mechanism is also such that if undue pressure is caused to be exerted on the drill due to the dullness of the cutting edges or to the lodging of a chip under the drill the drill is repeatedly retracted and advanced from the bottom of the hole into the intermediate retracted position until the cause for the excess pressure has disappeared or until the mechanism is stopped by. an operative. The mechanism for effecting this cycle of operations of the unit is not herein specifically illustrated as its specific construction is not necessary for an understanding of the present invention.

Each drill unit is mounted on a base 42 adapted to be secured in-any desired position on the table I6. The base carries an'electric'motor 44 which through speed increasing gearing 46, see Fig. 4, rotates a shaft 48 that has a telescoping connection with the drill spindle 56 rotatable in a head 52 slidable on a horizontal track 54 of the base 42. The drill 46 isthereby driven by the motor in any advanced or retracted position thereof. The base 54 is provided with a hydraulic cylinder 56 having a piston 58 therein which is connected by a piston rod 66 with the drill head 52 so that pressure applied alternately on opposite sides of the piston causes the drill head and the drill to reciprocate in opposite directions. The automatic advance and retraction of the drill into successively advanced positions in the work and the final movement of the drill into a fully retracted position is controlled by movements of the drill through a cam slide 62 that is secured to and is movable with the piston and the drill head. The cam slide 62 carries a cam 64 that has steps 66 and 68-thereon that are moved by movements of the cam slide into successive engagement with a pin I6 of a control lever I2 fixed to a vertical shaft I4 and having at its lower end an arm I6 that operates valve mechanism presently to be described. When the pin I6 and lever 12 are in the position illustrated in Fig. 4, the mechanism is set for rapid advance. When the pin "I6 is on the horizontal ledge I8 between the two steps the mechanism is set for slow advance. Engagement of the step 68 with the pin 16 causes the lever 12 to be moved away from the engagement of the cam block into a reverse position illustrated by the dotted line, this movement being assisted by a spring pressed plunger 86. The hydraulic piston is then moved backwardly and a cam block 82 fixed to said cam slide 62 engages the pin 16 and moves it toward the cam slide and into a neutral position midway between reverse and slow speed advance positions, where it is held until it is thrown into fast advance position either manually or under hydraulic control. The cam block 64 is at times locked to the cam slide by means not illustrated and is unlocked at times when the pin I6 is against the step 68 so that then the cam block is held stationary while the cam slide and the block advances. The amount of such movement determines the length of the slow speed advance of the drill and is determined by means including a series of cam dogs 83, see Fig. 3, which are carried by the cam slide and successively engage mechanism, not shown, carried by the cam block 64, on successive advance movements of the drill, to advance the cam block with the cam slide to trip the control lever 12 and efiect the reverse movement of the drill, the cam block 64 moving rearwardly with the slide. When the slide is in an intermediate retracted position determined by mechanism indicated generally at 85, Fig. l mechanism, not shown, is provided to move the control lever I2 inwardly into fast advance position whereupon the drill advances rapidly toward the work until the. control lever is moved into slow advance position by the step 66 of the cam. During the final retracted position the cam block 64 is reset automatically to an initial position near the neutral cam 82 so that the mechanism is in condition to repeat a second cycle of operations. Said cam block 64, thus constitutes accumulating stop means for progressively increasing the working stroke of the drill.

The mechanism is suppliedwith oil under pressure by means of a constantly operating pump 84 which receives oil from a sump or reservoir 86 and delivers pressure oil to the cylinder 88 of a compressed air accumulator 86 which is arranged tomaintain a constant pressure of oil on the system regardless of the number of drilling units which exit port is connected through a duct I64 with the inlet duct I66 of a speed controlling valve cylinder I68. Said cylinder has an exit duct II6 adjacent the inlet duct which is connected through a duct I I2 with the rear end of the bydraulic cylinder 56 and admits pressure fluid into the cylinder behind the piston in a direction to effect the advance of the dri1l. .The ends of the valve cylinder I66 are connected to exhaust ducts I I4 which conduct exhaust oil back to the reservoir 86. The front end of the hydraulic cylinder 56 is connected to a duct II6 which is open into the valve cylinder I66 between the pressure duct 96 and the right hand exhaust duct H4 and at times receives pressure liquid to act on the front end of the piston 58 in a direction to effect the retraction of the drill. The valve cylinder I66 is provided with spaced piston valves 8 and I26 therein connected to a valve stem I22 that is connected to a frame I24 operated by the arm I6 of the control lever 12. In the position of the piston valves illustrated pressure oil can flow from the pressure duct 66 through the valve cylinder into the pipe I64, theince through the speed controlling cylinder I 68 and thence into the rear end of the cylinder 56 to effect the rapid advance of the drill. Oil in the cylinder 58 in the duct II6 into the right hand end of the valve cylinder I00 where it flows through the duct II4 into the reservoir 86. When the pin I0 oi the control lever I2 is on the ledge I8 of the cam block 64 the piston valves H8 and I20 are so set that the piston II6 partially closes the exit duct I02 while the piston I20 completely closes the outlet of the duct II6 into the valve cylinder. The only escape of the back pressure oil from the operating cylinder 56 through the duct 6 is through a branch duct I26 controlled by a valve I26 which imposes considerable resistance to the flow of the oil. Under these conditions the infiow of oil to the operating cylinder 56 is partially throttled and, due to the restricted escape of oil to the forward side of the operating cylinder, 9, back pressure of oil is set up which opposes the free advance of the operating piston and hence gives a slow advance of the drill and also holds the drill against longitudinal vibration. The speed controlling cylinder I06 is provided with a piston valve I30 that controls the inlet port I06 and is urged by a spring I32 in a direction to clear the port and by back pressure the cylinder I00 and the piston, I20 is located to the right of the opening of the duct H6 to said cylinder. In this position of the valve high pressure oil from the duct 06 flows through the duct H6 into the front end of the operating cylinder thereby moving it rapidly toward retracted position, the oil in the cylinder in the rear of the piston flowing freely through the duct H2 and through the valve casing I08 and I00 into the left hand exhaust duct III. The automatic operation of the mechanism can be interrupted and the unit moved into fully retracted position by means of a manually or otherwise operated threeway valve I30 which receives pressure oil from the pressure main 02 and is movable from a neutral position in oppositely disposed positions where it can direct pressure oil to flow through ducts I36 and I 00 to the opposite-ends of a cylinder I00 and act in opposite directions on the pistons I02 and I 04 therein. The action of pressure oil on the piston I02 is to move it toward the right into engagement with a projection I06 of the frame I20 and to move said frame and the valve associated therewith into a reverse position, thereby effecting the reverse, movement of the drill unit into a fully retracted position. The action of the pressure oil in the piston I00 is to move said piston and the frame I 20 toward the left into a fast advance position of the valve to thereby initiate the cycle of operation of the drill unit.

The hydraulic control mechanism as so far described-is or'can be duplicated in the mechanism associated with the drill unit A and need not be further described.

For the purpose of preventing interference between the drills of the two units each unit has associated with its hydraulic system and interference valve 00 previously referred to, which valve,

' when operated. isolates its unit from the fluid pressure source and thus stops the drill from advancing. Associated with the interference valves is an interference-valve selector valve cylinder I48 which is common toboth units A and B, and a separate interference-position valve cylinder I associated with each drill unit and arranged to be operated thereby when the drill unit moves into interfering position. Each interference valve cyladapted to receive pressure fluid against the upper end thereof through a duct I56 in communication with an outlet duct I60, of the selector valve cylinder I 48. The arrangement of the valve 64 is such that the oil pressure acting on the bot+ tom end of the piston I54 from the duct 92 tends to maintain the piston in elevated position above the outlet duct I52 whereby to allow oil-to flow to its associated drilling unit. When, however, oil pressure is applied to the upper end of the larger operating cylinder I56 the total pressure on the piston in a closing direction is greater than that on the piston I54 in an opening direction and hence the piston I54 moves to the bottom of the cylinder and isolates the port I52 from the pressure source thereby preventing the operation of the hydraulic mechanism of the unit. The selector cylinder I48 has an exhaust port I62 which is disposed in the middle thereof or at the left of the outlet port I60 for. the unit B and at the right of the outlet port I 60 for the unit A and conducts exhaust oil to the oil reservoir or sump through a duct I63. Pistons I60, I66 and I68'are disposed in said cylinder in spaced and connected relation. The con cted pistons are freely movable in opposite dir ctions within the cylinder and are adapted to be moved into one end or the other end of the cylinder by one or ,the other of the interference-position valves I60 of the respective ,units and to remain in whichever position they. may have been moved until moved in the opposite direction. Each interference-position valve cylinder I60 is provided with an outlet duct H2 in the middle thereof which communicates through a duct lid with a separate end of the selector valve cylinder I48, the port of the valve of the unit B communicating with the right hand end of the cylinder and the corresponding port of the unit B communicating with the left hand end of the cylinder. Each interference-position valve cylinder has an upper exhaust duct I16 communicating through a duct IIB with the open oil reservoir 86. Pressure oil is constantly maintained in the bottom of the cylinder by a duct I60 which is connected with the pressure main 02.

A piston valve comprising a pair of spaced pistons I02, I00 is disposed within said valve cylinder I 00, the piston being connected by a valve stem I06 that extends upwardly above the top of the cylinder and is terminated close under or in engagement with a pin I located at one end ofalever I00 pivoted at itsother end to the base 660i the unit. The pin and lever are disposed beneath the movable head 52 of the unit and said head has a cam block I02 thereon and movable therewith which in a predetermined position of the head is adapted to ride over the pin I88 and depress said pin and its lever and. consequently to depress the valve stem I06. The cam block I02 is capable of adjustment longitudinally of the head 52 and of being secured to saidhead in any adjusted position by simple means not necessary to describe and is adapted to be set in such position as to depress the valve stem I86 when the cutting end of the drill arrives at the interfering point E, Fig. 5. When the valve stem is depressed the piston I 42 is depressed into a position where it isolates the outlet port I12 from the exhaust port I16 and the piston I84 moves into a position where the bottom of the cylinder is in communication with the outlet port I12 and hence establishes oil pressure 'in the duct I12. The operation of the interference-position valve of the unit B thus establishes oil pressure in the right hand end of the selector valve cylinder I48. This oil pressure acts first on the intermediate piston I66 and thence on the piston I68 to move the three pistons as far as they can go into the left hand end of the 'cylinder. In this position the piston I68 will be disposed between the right hand port I and the enlarged right hand end of the cylinder, the piston I66 will be disposed between the duct I62 and the left hand duct I60, and the piston I64 will be disposed in the enlarged left hand end of the cylinder. Hence the operating piston I56 of the interference valve 94 of the unit B is isolated from fluid pressure and thus the piston I54 is maintained in elevated or open position so that the operation of the interference-position valve I50 of its associated unit B does not effect theoperation of the hydraulic mechanism of the unit and the unit can continue to advance, assuming that the drill of the unit A has not yet advanced into interference-position. The above described operation places the interferenceposition valve I50 of the unit A in control of the operating piston I55 of the interference valve 94 of this unit. Hence when the unit A arrives at interference-position the cam of said unit operates its interference-position valve and places fluid pressure on the operating piston I 56 through the duct I14 of said unit and the selector valve I48. The pressure on said operating piston overbalances the pressure on the smaller valve piston and causes it to close thereby stopping the flow of pressure oil to the hydraulic operating cylinder of the unit and hence arresting the advance of the drill of itsown unit A beyond interfering-position. When, however,

the drill of unit B is retracted beyond interfer-.

lug-position, the interference-position valve thereof is released and the valve moves upwardly due .to the oil pressure on the bottom thereof and thus exhausts the pressure in the right hand end of the selector valve cylinder through they ducts I14 and I16 of the unit B. The selector valve pistons are now unbalanced due to the high oil pressure now existing solely in the left hand end of the cylinder and hence the pressure moves the pistons to the right hand end of the cylinder and into the position illustrated. In this position the pressure on the operating piston I56 of the interference valve of the unit A is exhausted through the exhaust duct I10 and hence the piston I54 of said interference valve is opened and consequently the drill of unit A starts to advance from interference-position. If the drill of the unit B should be again advanced it will advance only so far as interference-position and will then be stopped in the manner above described. With this arrangement the unit that arrives first in interference-position gains precedence over the other and ontinues to advance'and holds the other stationary in interference-position. The .unit that arrives at interference-position first continues to'advance until itis retracted automatically by the control mechanism associated with the cam block 84 whereupon the other unit takes precedence and starts its advance from interference-position. A unit that has lost precedence by reasons of its retraction can again advance to interference-position providing its cycle of operations has not been completed and will remain stationary in interference-position until the retraction of the advancing unit, whereupon the stationary unit will advance.

I claim:

1. A drilling machine comprising the combination of two drilling units, independent hydraulic mechanism for advancing the drills of each unit simultaneously along convergent lines into a potential interfering position, and means responsive to the movements of said mechanisms for causing the mechanism that arrives first in interfering-position to continue to advance and to stop the advance of said other mechanism into interfering-position and means subsequently to advance said other mechanism but only after the first mechanism has been retracted from interfering-position. r

2. A drilling machine comprising the combination of two drilling units, hydraulic mechanism associated with each unit for advancing and retracting the drill thereof independently of the other unit, a separate valve controlling the supply of pressure fluid to each of said hydraulic mechanisms, means operated by each unit when the drill thereof arrives in a predetermined position for closing the valve of said other unit and arresting the operation of said hydraulic mechanism thereof, and means for resuming the advance of the arrested mechanism following the retraction of the other mechanism.

3. A drilling machine comprising the combination of two drilling units, hydraulic mechanism for advancing and retracting the drill of each unit independently of the other unit, a valve associated with each unit for controlling the supply of pressure fluid to the hydraulic mechanism ,the'reof, selector mechanism for operating said valves selectively having means operated in a selected manner independently by each of said units when the drill thereof is in a predetermined position for arresting the operation of the hydraulic means of the other unit, and means for advancing the arrested unit following the retraction of the other unit.

4. A drilling machine comprising the combination of two drilling units, hydraulic mechanism associatedwith each unit for advancing and retracting the drill thereof independently of the other unit, a 'valve associated with each unit for controlling the supply of pressure fluid to the hydraulic mechanism thereof, means including a selector valve movable into alternate positions for effecting the alternate closure of said control valves, means including valves associated with said drilling units and arranged to be operated thereby when the drills of said units are in predetermined positions for effecting the operation of said selector valve to close the control valve associated with the other unit and arrest the advance thereof, and means for re-advancing the arrested unit following the retraction of the other unit.

5. A drilling machine comprising the combination of two drilling units each having hydraulic mechanism for advancing and retracting the drill of its unit independently of the other unit, a contral valve associated with each unit for controlling the supply of pressure fluid to the hydraulic mechanism thereof, selector mechanism controlling the operation of said valves, means including valves each associated with the separate one of said two units and operated thereby in a. predetermined position of the drill thereof for effecting the operation of said selector mechanism to arrest the operation of the hydraulic mechanism of the other unit, andmeans for readvancing the arrested unit following the retraction of the other unit from interference position.

6. A drilling machine comprising the combination of two drilling units arranged at an angle to each other, hydraulic mechanisms each associated with a separate unit for advancing the drills thereof along convergent lines to an interferingposition, interference valves each associated with a separate hydraulic mechanism for controlling the supply'of pressure fluid thereto, means associated with each drilling unit and operated thereby when the drill of said unit is in interferingposition for operating the interference valve of the other unit to disable the operation of the hydraulic mechanism thereof, and meansfor readvancing the arrested unit following the retraction of the other unit from interference position.

7. A drilling machine comprising the combination of two drilling units arranged at an angle, hydraulic mechanism separately associated with said units for advancing the drills thereof along convergent lines to an interfering-position, control valves separately associated with said hydraulic mechanisms for controlling the supply of pressure fluid thereto, selector mechanism for selectively operating said control valves, and means separately associated with each drilling unit and operated thereby in the interfering-position of the drill thereof for operating said selector mechanism to effect the operation of the control valve for the other unit to prevent the advance of said hydraulic mechanism.

8. A drilling machine comprising the combination of two drilling units each having a hydraulic mechanism associated therewith for advancing and retracting the drill of said unit independently of the other unit, a valve associated with each hydraulic mechanism for controlling the supply of pressure fluid thereto,.a second valve separately wsociated with each'unit and operated therebywhen the drill of said unit is in a predetermined position, means associated with said second valves for-operating the control valve of the unit associated with an unoperated second valve for preventing the advance of the hydraulic mechanism thereof, and means for advancing the arrested unit following the retraction of the other unit from interference position.

9. A drilling machine comprising the combination of two drilling units each having a movable head hat supports the drill, hydraulic mechanism for advancing and retracting'said head, and means including valve mechanism for automatically retracting and advancing said head, a source of fluid pressure, means including a normally opened control valve connecting each hydraulic mechanism separately with said source of fluid pressure, and means including a valve associated with each drilling unit and operated by said head in a predetermined position thereof for effecting the closing of the control valve of the other unit and the disabling of said hydraulic mechanism.

10. A drilling machine comprising the combination of two drilling units each having a movable drill carrying head, hydraulic mechanism for advancing and retracting said head, and means including valve mechanism for automatically effecting the retraction and advance of said head,

trol valve separately connecting said source of fluid pressure with each of said hydraulic mech=- anisms, means including selector mechanism operated independently by each head when it is in a predetermined position for operating the control valve of the other unit and for arresting the operation of said mechanism, and means respons'ive to the retraction of one unit from interference position for freeing the arrested unit for operation.

11. 'A drilling machine comprising the combination of two drilling units each having drill carrying heads that are movable along convergent lines to advance the drills into an interferingposition, hydraulic operating mechanism for independently advancing and retracting each head, means includingvalve mechanism controlled by the movements of each head for advancing and retracting said 'hydraulic mechanism, a source of fluid pressure, means including interference valves separately connecting said source with said hydraulic mechanisms, selectorvalve mechanism associated with both drilling units for operating said interference valves, and a separate interference-position valve associated with each of said units and operated thereby when the drill thereof is in an interfering-position for operating said selector mechanism in a manner to effect the operation of the interference valve for the other unit whereby to disable the hydraulic mechanism thereof.

12. A drilling machine comprising the combination of two drilling units, each having drill operating mechanism and hydraulic mechanism for advancing and retracting'the drills, a source of fluid pressure, means including a control valve for said hydraulic mechanisms separately connecting said source with said hydraulic mechanisms, hydraulic means for operating said control valves, a selector valve for operating said hydraulic means comprising a valve piston, and means operated by each of said units when the drill thereof is in a predetermined position for applying hydraulic pressure in opposite directions to said piston to cause it to move into a position to admit fluid pressure to the hydraulic means of the control valve of the other unit to arrest the operation of the hydraulic mechanism thereof.

13. A machine tool including independenthydraulic devices to advance a plurality of cutters simultaneously and independently along convergent lines into a potential cutter-interference position, means providing hydraulic circuits for said devices, and interference-preventing means including valve mechanisms controlling said circuits responsive to the advance of one cutter into said cutter-interference position to de-energize the hydraulic advancing devices of all other cutters and to continue the advance of said one cutter.

14. A machine tool including a pair of cutter operating mechanism, hydraulic devices each associated with a separate operating mechanism to advance their respective cutters simultaneously and independently along convergent lines into a potential cutter-interference position, means providing hydraulic circuits for said devices, and

interference-preventing means including valve mechanisms controlling said circuits responsive to the advance of one mechanism into said interference position to disable the hydraulic device and to arrest the advancing movement of the other cutter advancing mechanism and to conassociated hydraulic device to advance its cutter tion of two drilling units, independent hydraulic into interference position and to de-energize the circuit of the other hydraulic device and to arrest the advancing movement thereof with its associated cutter out of interference position.

16. A machine tool including a pair of cutter operating mechanisms, hydraulic devices each associated with a separate mechanism having means to advance their respective cutters simultaneously and independently along convergent lines to a potential cutter-interfering position, means providing hydraulic circuits for said devices, and interference-preventing means including valve mechanisms controlling said circuits and governed by the position of said mechanisms to efi'ect the operation of one hydraulic device to advance its associatedcutter into interfering position and to de-energize the hydraulic device of the other unit to prevent advance of its cutter into interfering position.

1'7. A machine tool including two cutter operating mechanisms, independent hydraulic devices to advance the cutters of said mechanisms simultaneously and independently along convergent lines to a potential cutter-interfering position, means providing hydraulic circuits for said devices, and interference-preventing means including valve mechanisms controlling said circuits and operated by the hydraulic device of that cutter that advances first into interfering position to arrest the advancing movement of the hydraulic device of the other unit.

18. A machine tool comprising the combination .of two cutter operating mechanisms, independent hydraulic devices for advancing the cutters of said mechanisms simultaneously and independently along convergent lin-es to a potential cutter-interfering position, means providing hydraulic circuits for said devices, and interferencepreventing means including valve mechanisms controlling said circuits and operated by the hydraulic device of whichever cutter arrives first in interfering position to effect the continued advance of the associated cutter and the halting of the advancing movement of the hydraulic device of the other cutter.

19. A drilling machine comprising the combinadevices for advancing the drills of each unit simultaneously and independently along convergent lines into a potential drill-interfering position, means providing hydraulic circuits for said devices, interference-preventing means including valve mechanisms in control of said circuits and responsive to the movement of said devices for causing the device that arrives first in a position corresponding to said drill-interfering position to continue to advance and to stop the advance of said other device into interfering-position and means responsive to the retraction of said first device to efiect the advance of said other device.

20. A drilling machine comprising the combination of two drilling units movable along convergent lines into a potential interference-position, independent hydraulic devices for advancing .and retracting the drills of said units, said devices 7 being simultaneously operative, a source of fluid pressure for operating said hydraulic devices, valves controlling the connection of said source of fluid pressure with each hydraulic device, and means operated by any one unit when the drill thereof is in a potential interference position for closing the valve of the other unit and arresting the operation of the hydraulic device thereof with the associated unit thereof out of interference position, whereby to prevent interferenceof the 21. A drilling machine comprising two drill holders movable toward each other into a potential drill interference position, hydraulic devices for reciprocating said holders, hydraulic circuits for said devices, means including advancing valve mechansms controlling said circuits and normally responsive to different positions of said holders to advance said holders independently of each other and simultaneously toward each other by a series. of reciprocating movements through said drill-interference position, and interferencepreventing means including interference-valve mechanisms controlling said hydraulic circuit and responsive to the positioning of any holder in said drill-interference position to disable the hydraulic circuit of the hydraulic devices of the other holder and to halt the advance of said other holder at such interference-position, said interference preventing means also being responsive to the retrac 'tion'of said one holder from interference position to effect the advance of said other holder into interference position.

22. In a step drilling machine, the combination of two tool members movable toward each other i into a potential tool-interference position, a hydraulic device associated with each tool member for moving it independently of the other, each hydraulic device including a cylinder, a piston connected to and movable with its associated tool member, a hydraulic circuit including means for delivering fluid to and receiving fluid from the opposite ends of each of said cylinders to cause reciprocation of the associated tool relative to the work, means movable in unison with each of said pistons and cooperating with a plurality of valve units for moving each of said pistons andthe associated tool independently of and simultaneously with the other piston and its associated tool in a series of progressively advancing reciprocating strokes in cycles, each cycle comprising a rapid traverse movement toward the work, a relatively slow feed rate movement through a portion of the work at a rapid traverse movement from the work, accumulating stop means separately associated with each tool holder and responsive to the feed movement 'in each cycle 'of its tool holder for progressively increasing the depth of rapid traverse in the succeeding cycle thereby advancing the feed range, and interference-preventing 'means including valve mechanisms controlling said hydraulic circuits and responsive to the movement of whichever one of the tool members it is that first advances into toolinterference position to permit that tool member to continue its cycle and to stop the other tool member from movement through tool-interference position.

ERIC J. HIRVONEN;