US2042247A

US2042247A - Machine tool

Info

Publication number: US2042247A
Application number: US688637A
Authority: US
Inventors: Louis H Blood
Original assignee: Cincinnati Milling Machine Co
Current assignee: Milacron Inc
Priority date: 1933-09-08
Filing date: 1933-09-08
Publication date: 1936-05-26
Anticipated expiration: 1953-05-26

Description

May 26, 1936. L. H. BLOOD v MACHINE TOOL Filed Sept. 8, 1933 4 Sheets-Sheet l LMH IW LIIII fll 3 v w c nioo 00/5 l-l. BL 000 M/ Straw,

y-26,1936. l.v H. BLOOD 2 042,241 I MACHINE TOOL Filed Sept. 8, 1933 4 Sheets-Sheet 2 May 26, 193s. H BLOOD 2,042,247

MACHINE TOOL Filed Sept. 8, 1953 4 Sheets-Sheet 3 Lou/s #34001) May 26, 1936.

| H. BLOOD 2,042,247

MACHINE TOOL Filed Sept. 8, 1953 4 Sheets-Sheet 4 awe/whom Lou/s Ii 51.000

Patented May 26, 1936 PATENT OFFICE MACHINE TOOL Louis 11. Blood, Cincinnati, om, assignor to The Cincinnati Milling Machine 00., Cincinnati, Ohio, a corporation of Ohio Application September 8, 1933, Serial No. 688,637

10 Claims.

This invention relates to machine tools and more particularly to an improved transmission and control mechanism therefor. I

One of the objects of this. invention is to provide an improved hydraulic transmission for machine tools which will yield a plurality of feed rates over a. wider range than conventional hydraulic transmissions now in use, and which will .be in stepped relation similar to mechanical gear transmissions.

Another object of this invention is to provide an hydraulic transmission which is capable of yielding a plurality of feed rates, but which utilizes only simple and inexpensive constant displacement pumps.

A further object of this invention is to produce a variable speed hydraulic transmission by utilizing a. plurality of auxiliary pumps of different volumetric capacity for volumetrically adding to or subtracting from the delivery of a principal constant displacement pump to obtain variation in rate.

An additional object of this invention is to provide a simple control mechanism for a multiple pump transmission in which a desired combination of pumps 'is connected to the operating cylinder to. produce a desired feed rate in one direction, and only a single same pump of that combination is' connected to the operating cylinder to produce a return quick traverse rate.

Other objects and advantages of the present invention should be readily apparent by refer- Figure 1 is a side elevation of one form of machine tool having this invention embodied therein. I

Figure 2 is a side elevation showing this in-. vention embodied in another form of machine tool. Figure 3 is a section on the line 3-3 of Figure 1, showing the method of driving the pumps.

Figure 4 is a section on the lined-l of Figure 3, showing the arrangement of the various pumps in the reservoir.

V Figure 5 is a section on the line 5-5 01 Figure 3 showing the construction for connecting the auxiliary pumps to the main drive gear. I

Figure 6 is a section on line 6-4 of Figure 1, showing details of the trip plunger.

Figure 7 isa section on the line 1-1 of Figure 1, a showing the stop valve operating mechanism.

' Figure 8 is a section on the line 88 of Figure 1, showing the details of the mechanism operated by the trip plunger.

Figure 9 is a semi-diagrammatic view of the 10 hydraulic circuit of the machine.

Figure 10 is a diagrammatic view showing the manner in which the auxiliary pumps operate to subtract fluid from the main flow.

Figure 11 is a diagrammatic view showing the 16 manner in which the auxiliary pumps operate to add fluid to the main flow.

Figure 12 is a detail section on the line l2--l2 of Figure 9.

Figure'13is a detail section on the line I3 4! 01 Figure 9.

This invention is particularly adaptable to machine tools such as planers, shapers, milling machines, broaching machines, and ;the like, in which a reciprocable slide is moved in one direc- 25 tion at a prescribed feed rate and returned in the opposite direction at a quick-traverse rate and will be explained in connection with a shaper, such as shown in Figure 1, as constituting one exemplification of this invention. 30

In this machine the toolslide I0 is moved over the work support I l in one direction to shave or remove a chip from the work and then returned at a rapid rate during which time the work support is indexed or given an incremental feed to 35 prepare for the removal of a subsequent chip.

An hydraulic motor is provided for eilecting this reciprocation, and as shown in Figure 9, is preferably of the piston and cylinder type. The cylinder 12 is in this construction carried by and moved with the slide l0 and consists of a. tubular portion, which at one end is fitted on and supported by the shouldered member I! attached to one end of the slide in, and at the other'end is fitted and'supported by a shouldered member 45:

H which is adiustably mounted in the other end or the slide 10. Bolts I! serve to force the member ll toward the member l3 to securely clamp the cylinder there-between and prevent leakage therefrom. 7 7

. A piston I6 is reciprocably moimted in the cyl-' inder l2 and connected by. the hollow piston rod I'I to a fixed bracket I! carried by the bed of the machine. The end portion i9 oi. .the piston rod, which flts in the bracket I8, is tapered and a lock nut 20 is threaded on the rear end of the v is considerably thicker than the other siile.

. positioning the piston rod so as to align a port 22 formed therein with a radial bore 23 formed in the bracket l5. Since relative sliding movement takes place between the member l4 and the piston rod H, the member H has been recessed to receive a packing material 24 which is adjustably compressed by the rotatable member 25 threaded in one end, of the member l4. The member 25 is provided with gear teeth 25 meshing with a worm wheel 21, which is mounted on the end of a shaft 28 for manual adjustment. It will thus be seen that there is a piston rod which is fixed at one end of the bed of the machine and that the piston secured to theiother end of the piston rod is supported by the cylinder l2 which is movable relative to the piston for effecting reciprocation of the slide l0.

As previously mentioned, the piston rod is hollow, or in other words, has a longitudinal bore 29 in which is fitted a tubiflar member 39, which, as shown in Figure 12 has an eccentric bore 3| formed therein so that one side of the member The tubular member 35 is fitted within the hollow piston rod and longitudinally positioned therein by means ofa shoulder 32 formed on the interior of the piston rod. The thicker side of the memv ber 30 is milled out at 33, as shown in Figure 12,

to provide a passage 34 between the port 22 and the right hand end of the piston l5. As shown in Figure 9, this passageway does not extend the full length of the member 30, but terminates at one side of the port 22 so that flow back and forth from the port 22 will enter the groove, and at the other end terminates at a radial hole 34' drilled in the side of the piston rod so as to form a connection between the passage 34 and the right hand end of the cylinder l2. The bore 3i serves to connect the' left hand end of the cylinder with a port 35 formed at the right hand end of the piston rod and in which is threaded pipe 35. The port 22 serves to supply fluid for eflecting return movement of the slideat a rapid traverse rate and-the port 35 serves to supply fluid for the feed rate. It will be noted that the left hand end of the cylinder. is of larger cubical capacity than the right hand end of the cylinder so that a given flow of fluid through the port 35 will not effect as fast a movement of the slide as the same flow through the port 22. There is thus a differential.

transmission contemplates the-provision of a.v

main hydraulic flow of constant predetermined volume which will yield an intermediate feed rate when coupled to port 35 of the slide motor andof auxiliary means for adding to or subtracting from said main flow predetermined volumetrie 'amoun -for varying the feed rate by steps above and low said intermediate rate. The manner of accomplishing this is as follows:

A main or principal constant displacement pump 31, Figure 9, is provided for supplying or delivering the main flow to the cylinderl This pump has an intake 39 for withdrawing fluid from the reservoir 39 and a delivery pipe 45 through which fluid is forced at a constant volume to the cylinder. The channel 40 may have a check valve 4i therein and an emergency relief valve 42, by means of which part of the delivery fluid may be by-passed to a reservoir through channel 43 in case of emergency. This relief valve may be of the conventional type, having a plunger 44 which is held by a spring 45 against the incoming pressure to normally close the port to the return channel 43. An intermediate channel 45 connects this relief valve to a port 47 of a stop valve 45 having a reciprocable plunger 49 mounted therein. When this plunger is in an operating position, such as shown in Figure 9, the port 41 is connected to the port 50 from which a pipe 5| extends to a port 52 formed in the rate and direction control valve 53. This valve has a reciprocable plunger 54 on which, is formed a pair of spools 55 and 55 which are so spaced as to form a mixing chamber 51. When this valve is in a position, such as shown in Figure 9, to yield-a feed rate, the port 52 is connected to a port 58 which is ultimately connected through the valve plunger 59 to the delivery pipe 35. The plunger 59 is integrally connected by the yoke 50 to the plunger 54 for simultaneous movement therewith. The plunger 59 has an annular groove 5| formed therein for connecting the port 55 to the delivery pipe 35 during feeding movements of the table.

During feeding movements of the table means have been provided for exhausting thefluid from the right hand end of the table cylinder and comprises a pipe 52 which connects the cylinder port 22 with port 53 formed in the valve 53. The plunger 54 is provided with an additional spool 54 spaced front the spool 55 to provide an .annular groove for connecting the port 53 to an exhaust port 55. For rapid traverse movements of the table the plunger 54 is shifted to the right whereby the port 52 is connected to the port 53 and the pipe 35 is connected to reservoir through movement of the plunger 59. It will thus be seen that the valve plunger 54 not only changes the direction of movement of the slide, but due to the piston differential, it,will effect feed'movement in one direction and rapid traverse movement in the opposite direction. The ratio of the piston differential may be such as to provide, for instance, a feed rate of 40 feet per minute and a quick traverse rate of approximately 200 feet per minute.

The feed rate of 40 feet per minute may be considered as the intermediate rate previously mentioned and auxiliary means have been provided for increasing and decreasing this rate by predetermined steps. This means comprises a plurality of auxiliary pumps, such as 55, 51 and 55, which maybe arrangedas more particularly shown in Figures 4 and 9. These pumps are of different capacity, the pump 55, for instance, being capable of yielding alone a feed rate of 8 feet per minute, the pump 59 a. feed rate of 16 feet per minute, and the pump 51 a feed rate of 40 feet per minute. It will thus be seen that if the pump 55 is operated to subtract from the main flow the final feed rate will be 32 feet per minute, while if the pump 55 is operated to subtract from the main flow a feed rate of 24 feet per minute of 16 feet per minute will be obtained. Similarly, these pumps may be operated to add to the.-

prime mover 69, which, as shown in Figure 1,

may be attached to the rear of the machine and connected by suitable means such as a chain 10 to a sprocket wheel 1|, shown in Figure 5. This sprocket wheel is rotatably mounted on a stud shaft 12 and has integrally secured thereto a common drive gear 13. As shown in Figure 3, the pumps are all submerged in the reservoir 39 and are'each provided with a flange 14 by which they are secured to the outer wall 15 of the reservoir as by bolts 16, suitable packing 11 being inserted between the flange and the wall to prevent leakage. The pump 31 has its drive shaft 18 extending through the outer wall and provided with a gear 19 fixed to the end thereof in constant mesh with the common drive gear 13. Thepump drive shafts 80, Ill and 82, of the

auxiliary pumps

66,61 and 68 also extend through the front wall of the reservoir and each is provided with ashiftable gear 83 splined on the end of the respective shafts. Each gear has an elongated hub 84 in which is formed an annular groove 85 for receiving a shifter fork 86 secured to the end of a vertical shaft 81. These shafts extend upward and are each provided with an operating handle 89, as more particularly shown in Figure 1. These sl'liftable gears thus serve as individual means for'connecting the various auxiliary pumps for operation by the prime mover and in any desired combinations to effect prescribed feed rates. In other words, these gears and the shifters therefor constitute a feed rate selecting mechanism.

In the present construction, the pump 61 is utilized only to increase the flow, whereas the

pumps

66 and 68 are utilized for both increasin or decreasing the main flow, Since these last two pumps are uni-directionally driven by the prime mover, valve mechanism has been provided for causing these pumps to act as delivery pumps or as exhaust pumps. This valve mechanism is more particularly illustrated in Figure 10, and since it is the same for both pumps, only one will be described. This valve mechanism comprises a housing 89 having two plungers 99 and 9| reciprocably mounted therein and connected together by a yoke 92 for simultaneous movement. The valve housing is also provided with four

ports

93, 94, 95 and-96. The port 93 is connected by a pipe 91 having a check valve 98 therein to the line 99. The port 95 is connected by the branch line I00 to the line 99 but it will be noted that there .is no check valve in this line. The port 94 is connected by channel IIII to the delivery port I02 of the pump, while the port 96 is connected by a line I03 to the intake port I04 of the pump. When the valve plungers are shifted to the left, as shown in Figure 10, a spool I05 interconnecting

ports

95 and 96 when in the po-' sition shown. From this it will be seen that the intake port I04 of pump 66 is connected through channel I03,

ports

96 and 95 and charmel I00 to the line 99, thereby acting to withdraw fluid from that line and discharge it through port I02, channel IOI, port 94 and space I06 to the reservoir. If the valve plungers 90 and 9| are shifted to the right, as shown in Figure 11, the plunger 90 will then interconnect

ports

94 and 93 and the plunger 9| will disconnect port 96 from port 95 and connect the same through the annular groove I01 to the reservoir.

The fluid will now be withdrawn from the reservoir through the annular groove I01, port 96, channel I 03, to the intake port of pump 66 and delivered through port I02, channel IOI,

ports

94 and 93 to channel 91, the pressure in this channel now opening the check valve 99 to permit passage of the fluid to line '99. It will be noted that at this time the port 95 is closed by the plunger 9|.

The valve plungers90 and 9| are shifted by the mechanism more particularly shown in Figure 3 and comprises a shifter fork I08 which engages the yoke 92 intermediate the plungers 90' and 9|. This shifter fork is pivotally mounted at I09 to a fixed part of the reservoir and operatively connected at the upper end by a pin and slot connection IIO to the shifter rod III. This rod has a pair of indents I I2 and I I3 formed therein for engagement by a spring pressed ball 4 which serves to hold the valve in either-one of its two positions. The rod, II I extends outward to the side of the machine where it is provided with an operating knob I I5.

Whenit is desired to change the feed rate above or below the intermediate rate produced by the pump 31 the desired pumps necessary to produce the prescribed rate are connected through their shiftable gears to the common drive gear 13,

while the remaining pumps that are not being used are disconnected from the main drive gear.

If pumps Eli-and 68 are being used, either alonethe relief valve 42 and need not be further described. After the fluid passes through this relief valve it flows through line 9 to a port I20 formed in the stop valve 48. This port is connected when the ,valve plunger 49 is in the position shown in Figure 9 to a port I2I,.which is connected by a channel I22 to a port I23 formed in the valve 53. Due to the fact that the flow in line I I9 may be in either direction it will be apparent that-the relief valve 1 might tend to close when the line .99 is being utilized as a suction line for

pumps

66 and 68 when the latter nel I I9 but will close during pressure flow in the.

opposite direction.

The port I23, it will be noted,opens into the mixing chamber 51 in valve 53 and the plunger 54 is provided with a spool I25 intermediate spools 55 and 56, and this spoolQis cut away on opposite sides, as more particularly shown in Figure 13, whereby the incoming fluid from port 52 will combine with the incoming fluid through port I23 to increase the feed rate, or part of the fluid incoming through port 52 will be subtracted by outward flow through the port I23. This spool serves to prevent turbulence in the flow and thereby causes smoother operation of the machine. It will also be noted that these ports are so arranged that when the plunger 64 is shifted toward the right that the port 52 will be disconnected from port I23 so that no matter what combination of auxiliary pumps is utilized to provide a prescribed feed rate only one pump will be utilized to effect the rapid traverse rate and it will always be the same pump, thereby providing a uniform quick traverse rate. Attention is also invited to the fact that the plunger 59 has a tapered end I26 which will be opposite the port 56 and the port I21 so as to prevent clashing of the return flow through pipe 36 and the exhaust flow from the auxiliary pumps when the same are being used for increasing the feed rate and thereby effecting'a more streamline flow to the reservoir and preventing turbulence therein.

The rate and direction plunger 54 is adapted to be shifted by fluid operable means and to insure a copious supply of fluid for this purpose a small accumulator I26 is attached to the valve housing 53. This accumulator comprises a chamber I29 in which is reciprocably mounted a plunger I30 having a bore I3I formed in one end thereof for receiving a strong spring I32. F'luid is preferably supplied to this chamber from the pipe I because this pipe is supplied from the continuously actuated pump 31 and therefore is always under pressure. As shown in Figure 9, a branch line I33 connects this pipe to the port I34 of the accumulator, the pressure forcing the plunger I30 to the left, thereby enlarging the chamber and affording an auxiliary supply if for any reason the pressure in line 5| should drop below the pressure which the spring I32 is capable of developing. In order to prevent loss of pressure when the accumulator acts, a check valve I35 has been inserted in the channel I33 in order to isolate the accumulator from its supply line 5| when the pressure therein drops below a predetermined minimum. v

A port I36 connects the accumulator chamber I29 with a pilot valve comprising a shiftable plunger I31 having spools I38 and I39 which are so spaced that when the plunger I31 is moved to the right, or in other words to the position shown in Figure 9, the port I36 will be connected to the port I40 through which fluid is supplied to the right hand end of valve 53 and the port I4I at the opposite end of valve 53 will be connected to the exhaust space I42. Plunger I31 is adapted to be shifted to a left hand position in order to connect port I36 with the port- I 4I and connect the port I40 with the exhaust space I43. It willthus be apparent that when pressure is supplied to the port I40, the valve plunger 54 and associated plunger 59 will be shifted to the left to cause feed-- ing movement .of the slide, and when pressure is supplied to the port I the plungers 54 and 59 I will be shifted to the right to cause rapid traverse movement of the slide.

The pilot valve plunger I31 is adapted to be automatically shifted by the trip mechanism more particularly shown in Figures 6 and 8. As

there shown, a trip plunger I44 is oscillatably mounted in a fixed part of the machine and has a trip lever I45 secured to the upper end and adapted to be engaged by suitably spaced trip dogs I46 and secured in the usual manner by bolts slidably mounted in a T slot carried by the slide I0. A lever arm I41 is keyed to the end of plunger I44 and is adapted to alternately engage a pair of pins I40 with a predetermined amount of lost motion, said pins being carried by a gear segment I49. Also secured to the lower end of the plunger I44 is a detent brake I50 having a pair of indents formed on the periphery thereof and adapted to be engaged by spring pressed detent I5I. This constitutes a conventional'form of lost motion trip mechanism.

The gear segment I49 meshes with a rack bar I 52 extending longitudinally along the side of the machine and operatively engaging a pinion I53 secured to the upper end of an oscillatable shaft I54. This shaft extends downward toward the reservoir and is operatively connected with the pilot valve plunger trip shaft I55 by means of pinion gears I56. The lower end of the shaft I55 I51, formed in the end of the pilot valve plunger I31. ated by means of the control lever I58 which is pivotally mounted at I59 on the side of the machine, the pivoted shaft having a gear segment I60 secured thereto and operatively meshing with rack teeth I6I formed onthe under side of the rack bar I52. It will now be seen that when the plunger I44 is oscillated in either direction by the trip dogs the pilot valve plunger I31 will be shifted either to the right or to the left to effect power shifting of the rate and direction determining valve plunger 54 and that this plunger may also be power shifted under manual control of the lever I56.

Since the plunger 54 only has two operative positions and both of those are running positions, the stop valve 48 has been interposed between the pumps and valve 53 for stopping the machine. The stop valve plunger 49 is operatively connected to a crank I62, as shown in Figure '7, having integral therewith the manually operable lever I63. When the plunger 49 is shifted from the running position shown in Figure 9 toward the right the port 41 leading from pump 31 will be connected to port I64 which is connected to the reservoir through channel I65. Also the port I20 leading from the-auxiliary pumps will be connected to port I66, also leading to reservoir through channel I61, and the ports 50 and I2I will be interconnected, thereby keeping these channels full of oil.

There has thus been provided an improved bydraulic transmission for machine tools such as the shaper shown in Figure 1 or to'the broach as shown in Figure 2, comprising a first pump which is adapted to supply and maintain a main flow which may be utilized in conjunction with a piston differential for obtaining a feed rate in one direction and a rapid traverse rate in the opposite direction and a plurality of auxiliary pumps for adding to or subtracting from said main flow to increase or decrease the volume thereof and in which said auxiliary pumps are so connected to the main flow channel that they will be entirely disconnected from said channel duringra-pid traverse movement of the slide.

What is claimed is:

1. In a machine tool having a work support and a tool support the combination of means for effecting relative movement therebetween at a plurality of feed rates or at a rapid traverse rate including a piston and cylinder, said piston having differential pressure areas on opposite sides thereofi a constant displacement pump alternately connect- The shaft I54 may also be manually oper-,

ible to opposite ends of the cylinder for effecting feeding movement or quick traverse movement be-' tween the supports and a plurality of pumps automatically connectible with said constant displacement pump when effecting a feed movement to increase or decrease the flow thereof to provide additional rates of feed movement between the supports, and automatically disconnectible from said constant displacement pump when efiecting a quick traverse movement whereby said quick traverse movement will always be efiected at the same rate.

2. In a machine tool having a work support and tool support the combination of means for efiecting relative movement therebetween at a plurality of feed rates including an hydraulic motor, a supply line for said motor, a constant displacement pump coupled to said supply line for effecting one rate of movement of the motor, an additional constant displacement pump having intake and delivery ports, means to start and stop said additional pump, a fluid reservoir, 'a first branch line for connecting said delivery port to the supply line, a second branch line for connecting the intake-port to said supply line, valve means operable when one of said branch lines is connected to its respective port for closing the other branch line, and a check valve in the first branch line for preventing return flow to said additional pump when the same is stopped.

3. In a machine tool having a work support and a toolsupport the combination of means for efiecting relative movement therebetween including an hydraulic motor, a constant displacement pump, a plurality of auxiliary constant displacement pumps, valve means for connecting said pumps to the motor including a-valve housing having a first port connected to said constant displacement pump and a second port connected to said auxiliary pumps, a supply line to said motor for effecting 'feeding movement thereof, a second supply line to said motor for eifecting rapid traverse movement thereof, shiftable means in said valve having a first position for simultaneously connecting both of said pump ports to the supply line and a second position for connecting only one of said pump ports to the second supply line of said motor, and additional means simultaneously operable upon movement of'said valve means to its second position to connect the first supply line of the motor and the auxiliary pump port to reser- 4. In a machine tool having a work support and a tool support the combination of means for effecting relative movement therebetween including an hydraulic motor, a constant displacement pump, a plurality of auxiliary constant displacement pumps, valve means for connecting said pumps to the motor including a valve housing having a first port connected to said constant displacement pump and a second port connected to said auxiliarypumps, a supply line to said motor for. efiecting feeding movement thereof, a secondsupply erable upon movement of said valve means to its second position to connectthe first supply line of the motor and the auxiliary pump port to'reservoir, said means including an auxiliary valve plunger and means on said plunger for diverting the output of all of said pumps to the feed port of said motor and to a second position for connecting only the first-named pump to the rapid traverse port of said motor, and fluid operable means for shifting said valve including an accumulator and a trip operable pilot valve for selectively coupling said accumulator for the shifting of said control valve.

6. In a machine tool having a work support and a tool support the combination of trip controlled power means for effecting relative movement therebetween including a fluid operable motor having a feed port and a rapid traverse port, a constant displacement pump, a plurality of auxiliary pumps, a rate and direction determining valve shiftable to a flrst position for connecting the output of all of said pumps to the feed port of said motor and to a second position for connecting only the first-named pump to the rapid traverse port of said motor, fluid operable means for shiftin said valve including an accumulator and a trip operable pilot valve for selectively coupling said accumulator for the shifting of said control valve, means coupled to said constant displacement pump for supplying said accumulator, and a check valve for preventing return flow to said pump when the accumulator discharges.

7. A machine tool having a work support and a tool support, means for efiecting relative movement between the supports including a piston and cylinder one of which is fixed and the other connected to one of said supports, said cylinder having a feed port and a rapid traverse port, means.

shiftable means-for selectively coupling the remaining pumps for operation by the prime mover in accordance with the feed rate desired, valve means for selectively coupling all of said pumps to the feed port of the cylinder and a trip operable device for shifting said valve means to a position connecting only the constantly driven pump to the rapid traverse port of said motor and the remaining pumps to the reservoir.

8. In an hydraulic system having a delivery channel connected for operation of a fluid operable device, the combination of means for supplying variable quantities of fluidto said channel to effect variableoperation of the device including a first constant displacement pump, a second constant displacement pump and a plurality of auxiliary constant displacement pumps, a prime mover for actuation of the pumps, means connecting the prime mover for continuous operation of the first pump, selective means for conmeeting the remaining pumps to the prime mover for individual or joint actuation thereby, a com-- mon reservoir for supplying the intakes of all of said pumps, individual means for connecting the output of the second pump and the auxiliary pumps to said channel in parallel, each 01' said means including a check valve operable to permit fiow from the pump to the channel during opera'tion of the respective pump, but to prevent fiow from the channel to the pump when the same is disconnected from the prime mover.

9. In a machine tool having awork support and a tool support, the combination of means for eflecting relative movement between the supports including an hydraulic motor having a difi'erential piston, a pair of delivery channels, a constant displacement pump permanently connected to one delivery channel, a plurality of additional constant displacement pumps of diflerent volume selectively connectible to the other delivery channel, a pair oi. motor channels, valve means having a first position for connecting both delivery channels to one of said motor channels to efiect difi'erent rates of motor movement in one .direction, and a second position for connecting said one of said delivery channels to the remaining motor channel to effect motor movement in the opposite direction at a predetermined fixed rate.

10. In a machine tool having a work support and a tool support, the combination of means for eflecting relative movement between the supports at a plurality of rates in one direction and at a first constant rate in the opposite direction including an hydraulic motor having a differentlal piston, a pair of fluid delivery channels, a constant displacement pump permanently connected to one of said channels, a plurality of ad-' ditional constant displacement pumps of different volume selectively connectible to the other channel, a pair-of motor conduits, valve means having a first position for connecting both delivery channels to the motorconduit connected to the end of the piston having the larger area, and a second position for connecting the first named constant displacement pump to the motor conduit leading to the end of the piston having the smaller area, and means trip operable by the moving support for shifting said valve means from one position to the other.

LOUIS H. BLOOD.