US3882640A

US3882640A - Portable precision hole finishing device

Info

Publication number: US3882640A
Application number: US401531A
Authority: US
Inventors: Gordon James Watt
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-08-19
Filing date: 1973-09-27
Publication date: 1975-05-13
Anticipated expiration: 1992-05-13

Abstract

A portable machine tool utilizing special features of outlet restrictor hydrostatic bearings in combination with conventional finishing tools, such as grinding wheels, single point tools, lapping tools, chemical milling, and electric discharge tools; with appurtenances for storing, shipping, mounting, lubricating, driving, and feeding in practical use.

Description

United States Patent Watt DEVICE lnventor:

PORTABLE PRECISION HOLE FINISHING Gordon James Watt, Apt. 106, 245

Unquowa Rd., Fairfield, Conn.

Filed: Sept. 27, 1973 Appl. No.: 401,531

Related U.S. Application Data abandoned.

Continuation of Ser. No. 172,985, Aug. 19, 1971,

U.S. Cl. 51/34 H; 51/165.93; 90/14 Int. Cl B24b 5/40 Field of Search 51/34 R, 34 H, 34 J, 38,

[56] References Cited UNITED STATES PATENTS 12/1924 Thomas 308/4 A Whitman 90/14 Primary ExaminerAl Lawrence Smith Assistant Examiner-K. J. Ramsey Attorney, Agent, or FirmLadas, Parry, Von Gehr, Goldsmith & Deschamps [5 7 ABSTRACT A portable machine tool utilizing special features of outlet restrictor hydrostatic bearings in combination with conventional finishing tools, such as grinding wheels, single point tools, lapping tools, chemical milling, and electric discharge tools; with appurtenances for storing, shipping, mounting, lubricating, driving, and feeding in practical use.

5 Claims, 7 Drawing Figures PATENTEDHAYWIQYS 2.882 640 SHEET 2 BF 2 al/m 5/27 PORTABLE PRECISION HOLE FINISHING DEVICE This is a continuation of application Ser. No. 172,985 filed Aug. 19, 1971, now abandoned.

BACKGROUND OF THE INVENTION Ordinary methods of producing holes by machines involve mounting the work on a stable base equipped with spindles, slides, drives, and other controls. The finishing tool is mounted on a cantilever bar or shaft also attached to the base and fed axially through the hole in the finishing operation. Quality and precision suffers from compliance of the machine, spindle runout, vibrations, thermal gradients, and friction in the moving parts. Accuracy in long holes is particularly difficult to attain.

Long straight holes are produced by drilling and reaming, outstanding examples being the gun drill and oil well rig. Holes produced in this way are not exceptionally round. Long holes tend to wander from the desired axis because the cutting tool leads its supports into the hole.

Good roundness and surface finish is accomplished by honing and lapping, both being self generative processes when properly controlled. They are more an art than a science, however, so the results are not consistent. It is difficult to control the diameter especially when the hole is long.

Others, including this petitioner, have invented feedback systems to influence the tool holder or spindle in response to sensors which detect bending or other defects in the working procedure. Such systems are expensive and difficult to maintain. Electronic and hydraulic controls are susceptible to pick-up from their own power sources or the shop environment. Particles and lubricants often produce errors in sensing systems which are used to monitor dimensions.

Porath in his U.S. Pat. No. 3,496,806 discloses the use of a hydrostatic bearing to guide a boring tool through a hole for finish boring. He has aimed his invention toward external dynamic control by using individual pads for bearing support. Such a bearing tends to pick up irregularities in the bore and to amplify them in the boring process because the tool leads its supports into the hole by a substantial distance. Used passively without external control, his apparatus relies heavily on the accuracy of the bore in the guide member and its alignment on the supporting machine base.

The present invention depends on characteristics of an outlet restrictor bearing, such as the flexible membrane bearing described in my copending application Ser. No. 159,608 filed on July 6, 1971 now U.S. Pat. No. 3,827,766. Other outlet restrictor bearings like that of Adams U.S. Pat. No. 3,112,140 and that of Arneson U.S. Pat. No. 3,305,282 hav'e equally desirable features in that bearing position and runout depend primarily on the quality and roundness of the dissenses average position in the bore and feeds back pressure changes to the main bearing area.

My invention is related to the art suggested by the individual principles and practices referenced in the foregoing and combines certain good and basic features into a useful machine for finishing cylindrical holes in a precise and economical way. At the same time it teaches the way to get around such things as machine compliance, vibration, alignment and thermal distortion as well as the inaccuracies associated with overhung supports, bearing surfaces, and processes which are not self generating.

SUMMARY OF THE INVENTION An' essential feature of the invention is the physical relation between the cutting head and the outlet edge (sensor edge) which locates the tool in the bore. The tool and sensor edge are adjacent along the axis so that any angular misalignment of the shaft carrying the two has negligible effect on the radial displacement between them. Position of the bearing which carries the shaft through the bore is determined primarily by the average location of the sensor edge with respect to the section of the bore which it covers. If the sensor edge is perfectly round, its average position is the same in any angular position of the shaft as it turns.

It is an object of my invention to provide a portable precision forming device which is capable of finishing long straight cylindrical holes by cutting, grinding, lapping, polishing, or by means of electrochemical or discharge machining. The machine is conceived along the lines of an oil well rig in that it is carried to the site of the hole with its driving, feeding, and lubricating appurtenances; the cutting head is attached to a bearing rotor element which is capable of following the finished portion of the hole both radially and in axial direction without relying on the stiffness of the driving shaft for direction; and the driving shaft is the source for angular rotation or torque, axial feed or force, and for lubrication to the bearing and cutting tool.

In drilling and reaming operations where direction and position of the hole are important a guide bushing may be used to locate the tool where it enters the hole. The machine disclosed here has a housing for the bearing element which houses the bearing and cutting head for storage and shipment; which mounts on the workpiece to support the bearing initially to guide the cutter and bearing into the hole; and which may be used to support the feed and drive mechanisms for the shaft in cases where a certain amount of heat and vibration can be tolerated. In cases where extreme accuracy and high finish is required, the drive and feed mechanisms may be isolated from the bearing and cutter by a flexible coupling which does not transmit heat or vibration from the motors.

The present invention is conceived to be a practical application for the flexible membrane hearing which is disclosed in my aforesaid copending application. Certain modifications to said bearing are described for this application. In particular it is necessary to cut the fluid feed manifold in the bearing surface instead of in the bore. This does not change the basic principles involved in the description for the flexible bearing.

Other outlet restrictor bearings may be used for the machine described here. The important factor is the ability of the bearing to provide rigid support radially and in axial direction. A pair of opposed outlet restric- 3 r bearings with sensor edges at either end will follow guide bushing and finished portion of the hole with xtreme accuracy both for roundness and direction. lexible membrane bearings offer additional capability )r damping and control which may be important for ertain applications of the machine.

Cleanliness is an important factor for bearing operaon. The fluid supply needs to be filtered to remove articles which are near the size of the clearance beveen the sensing surfaces and the bore. This is usually )mething like five microns. Outlet bearings are self :avenging in that flow is always outward from the earing surface, over the sensor edge, and toward the utter. Fluid velocities are high in the outlet region and 1e clearance is close. Cutting debris or liquids do not et into the bearing through this course.

When more than a few hundred millionths of an inch eeds to be removed in the hole finishing operation, it my be necessary to use more than one size of bearing. 'herefore the bearing elements need to be economical nd easy to change. It is an object of the invention to rovide a practical machine which is easy to set up, asy to use, and economical to operate. The concept ere is to build accuarcy and rigidity into the machine y making it compact rather than making it large.

One practical use for the present invention is in the oring and grinding of holes in cylinder blocks or in fin- :hing cylinder liners after they have been inserted. Anther is for producing long straight holes in tubes where ccuracy is important. By proper selection of materials nd lubricants the machine is adaptable to use at high.

amperatures. It may be run submersed in the coolant r electrolyte even though air is used to lubricate the earing.

In usual machine arrangements for cutting and grindig, forces generated between the work and the tool end the machine to force the tool away from the work. fthe tool is rotated rapidly, it must be dynamically balnced because it sets up vibrations which are amplified y the machine structure. The machine disclosed here -rovides extreme stiffness between the cutting tool and he work. Damping effects in the bearing are high and he bearing is linear in its elastic characteristics.

One objective of this invention is to control the cuting radius by controlled imbalance of the cutting head. Vhen the tool is rotated, an off axis weight may be used produce centrifugal forces to overpower the cutting orce. Equilibrium is reached when said centrifugal orce and cutting force are matchedby the restoring orce of the bearing. Those skilled in the art wil recognize that in so doing the tool can be drawn from the work after rotation is stopped, with no tool mark left in he work surface.

Appurtenances for supplying the necessary fluids, lriving the shaft and translating it axially, means for .lignment and control, attachments and supports, and inishing techniques, any or all of which may be pecuiar to a given application, are outside the scope of this nvention. Certain new manufacturing methods and means for control are taught by the invention and made )OSSlblC by the peculiar interfaces between cutting lead, outlet restrictor bearing, guide bushing, workziece, and fluids each together and together as a whole.

The invention makes possible a new economy for )ICCISIOI'I hole finishing. An unusual stiffness and stabilty is attained through the compact structure. A highly )recise boring or grinding machine may be transported to the work and quickly set up to. run. The flexible membrane bearing is extremely stiff, extremely true, and controllable. Other similar forms of. embodiment,

and use are contemplated and none be restricted by a detailed description of the preferred embodiment.

BRIEF DESCRIPTION OFTHE DRAWINGS FIG. 1 is a diagram showing the usual geometry and force relationships encountered in finishing a cylindrical hole on a machine.

FIG. 2 is a diagram similar to FIG. 1 showing the principles of the present invention. 7

FIG. 3 is a drawing indicating the preferred embodiment of the invention using aflexible membrane bearing and a grinding wheel.

FIG. '4 shows in perspective three basic types of hy- J drostatic bearings which are used for spindles and guides in machine tool applications. Force vectors and. I

FIG. 7 is an exploded view of a hole finishing appara-' tus exclusive of the power and controls, It shows the preferred embodiment of the bearing and cutter, a guide bushing used for cylinder blocks, a motor drive unit with hydraulic cylinder for rotation and feed, and

a housing for storage and shipment.

DETAILED DESCRIPTION The conventional way to builda machine. to form; precision holes is to start with a frame or bed and equip it with various guides, slides, spindles, and holders. Ex-. amples are lathes, jig grinders, boring mills, and the I like. A typical arrangement for boring a hole is shown in FIG. 1. This is not, unlike the disclosure of Porath.already referred to in the background discussion. The.

workpiece 11 is mounted on the machine so that it may. turn and/or slide on its axis. A guide bushing 12 may be mounted near the work on the machine frame l3'with the freedom to turn or slide with the workpiece in order to strengthen the tool holder 14 where it enters the 7 hole. The hole itself may be used to guide the holder as illustrated in FIG. I presuming that the machine frame a is rigid and that its spindles and slides remain aligned.

The important factor to consider is where the guiding surfaces and forces which align, the tool holder are located axially with respect to the cutting surface of the tool. These positions are indicated in the drawings by F for Force, 3 for guiding surface, and c for cutting surface. It is assumed that g produces F which in turn locates 0 through the rather complicated compliance of the machine and the work. What hurts most when bending occurs is the axial separation between the functional parts. The condition as shown in FIG. 1 is.

bad because the tool cutting surface is overhung from the surfaces which guide the tool holder. Bending of l the drive shaft 14 or portions of themachine frame 13 can move the cutting surface relative to the workpiece and produce machining errors.

Forces produced by the cutting surface c and th guiding surfaces g react to determine the location of V the surface produced by c. In general the force produced by the cutting action should be much lessithan I the force produced by the guiding surface. In the case of hydrostatic bearings, the ratio of F at g to the displacement of the guidance surface is called the bearing stiffness. For outlet restrictor bearings, stiffness is often greater than that of the composite supporting structure and is constant for the range of forces normally encountered in practical use. The present invention presumes a selection of design parameters for bearing and cutting tool which produces an extremely well defined axis of rotation.

The preferred arrangement for my invention is shown by the diagram in FIG. 2 which refers to the same parameters. The shaft is quite flexible and connected to the tool holder 16 through a universal coupling. The tool holder 16 is an outlet restrictor hydrostatic bearing like the flexible membrane bearing described in my aforesaid copending application. This bearing has guidance surfaces g at either end. The cutting head c is mounted on one end of the bearing as close as possible to a guiding surface g (sensor edge). Restoring forces F are inside the guidance surfaces and distributed over the main bearing area. The bearing frame 16 is extremely stiff compared to the tool holder 14 shown in the first figure.

The guide bushing 12 in FIG. 2 is mounted on the workpiece 11 and held rigidly thereto. The machine frame 13 in this case only serves to support the workpiece and to guide the shaft 15 in approximate alignment with the hole axis. The drive motor and feed cylinder are part of the machine frame. Machine deflections and vibrations are only reflected into the cutting action through inertial forces and some slight friction in the universal joint. The tool holder is held in strict alignment with the axis determined by the surface of the guide bushing and the finished surface of the hole.

The preferred embodiment of the tool holder 16 and cutting head 17 is shown by the drawing in FIG. 3 which is the plan view of a cylindrical object. The tool holder 16 is a flexible membrane bearing whose frame is a thick cylinder appropriately bored, drilled, and grooved to mount an eccentrically bored bushing 18, the universal joint 19, and to supply fluid to the manifold 20. The cutting head 17 may have a slightly eccentric shaft which matches the eccentricity of the hole in the bushing 18. The mass center of the cutting head and/or the bushing may be well off the bearing axis. The bearing surface is formed as an axially separated pair of cylindrical flexible membranes 30,31. Membrane 30 is supported at its opposed ends by raised

lands

32, 33 of the bearing frame which leave a space 34 underlying membrane 30 for accommodating pressure-induced inward deformations of membrane 30. The supporting arrangement for membrane 31 duplicates that for membrane 30.

Fluid to pressurize the bearing is fed through the shaft 15, through the universal joint 19, and through the frame of the bearing into a groove which goes completely around the outside of the frame. This groove is between the lands which support membranes 30,31 around the mid section of the bearing frame. Holes are radially drilled through the bearing frame to universal joint 19 at equal intervals around this groove to provide fluid passageways. The frame surface is relieved by a shallow groove 35 around the mid section deep enough and wide enough to serve as a manifold for the flexible membrane bearing. Fluid which flows across the sensor edge 36 at the cutter end of the bearing may also serve as a coolant for the cutting operation. If a separate coolant or lubricant is required it may be applied directly to the tool without risk of contaminating the bearing.

Different types of hydrostatic bearings are depicted in FIG. 4 by perspective views of the bearing surfaces. FIG. 4a shows an orfice bearing with recessed pads. Guidance g comes from the average clearance around each pad and results in a restoring force F produced by a change in pressure within the recessed area. Bearing action is lumped in areas around the periphery and toward the mid section. This results in the kind of support indicated in FIG. 1 where guidance is required from the machine frame to maintain axial alignment.

The bearing of FIG. 4b is illustrative of a porous bearing. The bearing action of a porous bearing resembles that of an orfice bearing except that guidance g and force F are more evenly distributed over the bearing surface. Bearing action takes place toward the mid section. One advantage of this bearing over the orfice bearing is smooth rotation. Both bearings are not exceptionally stiff or stable nor do they maintain good axial alignment.

The basic form of an outlet restrictor bearing is illustrated in FIG. 4c where the flexible membrane bearing is used as an example. Guidance g is evenly distributed around the outlet edges. The restoring forces F which respond to displacement are near enough to the edges to provide axial alignment as well as centering action. This is a low clearance bearing which is exceptionally stiff and stable. It is eminently suited to the arrangement shown in FIG. 2 which shows the basic arrangement of components for my invention. One object of the invention is to teach the use of outlet restrictor bearings in this improved machine configuration.

A practical application for an apparatus embodying the present invention is illustrated in FIG. 5. Here the workpiece is a cylinder block with a cylinder liner. The guide bushing is held in place by a flange with appropriate fastenings and means for alignment. The bushing 12 has an accurately formed bore with diameter to match the hole to be finished. The bore is long enough to accomodate the bearing 16 and start the cutting head 17 into the work. As the tool feeds into the hole, the leading edge of the bearing guides on the finished surface. The tool 17 tracks the average surface sensed by the guiding edge within the capability of the bearing to provide centering action. For the type of bearing used here decentering is only a few microinches per pound of decentering force.

Another application which is difficult to accomplish on conventional machines is the finishing of long straight round holes in a tubular piece such as a roller. It may be desirable to finish such holes at elevated temr perature or other environmental conditions which may deform the piece when in use. In FIG. 6 the hole finisher disclosed here is shown mounted at the end of a long hollow tube. Aside from mounting details the operation is as described for FIG. 5. What is to be emphasized is the compactness and portability of the apparatus even when in use. It is easy to see that the tube may be placed in a vertical position for processing if it is important to eliminate gravity sag.

Some of the necessary appurtenances are shown in FIG. 7 as they relate to the equipment already described. One is a drive and feed assembly comprising a mounting flange 21 which must be held in approximate alignment with the guide bushing 12 and prevented from rotating or moving axially with respect to the work; a drive motor 22 with a coupling which permits the shaft 15 to move axially while being turned by the motor; and a hydraulic cylinder 23 which is capable of moving the shaft in an axial direction by providing differential pressure to a piston attached to the end of the shaft. Said piston must be free to rotate in the cylinder while it is being fed along the axis. The cylinder may also supply fluid to the bearng through the hollow shaft from one side of the piston or both sides.

A shipping and storage container 24 is used to protect the machine components which fit snugly inside when its flange 25 is fastened to the flange 21 of the feed and drive unit. Power supplies and controls are necessary but their form is not vital to this disclosure. Apparatus embodying the present invention may be supplied in different sizes and load capacities depending on the work to be done. Different cutting heads may be used to produce certain finishes or to work certain materials. The flexible membrane bearing is not the only type of outlet restrictor bearing which can be used. These and other points are made in the claims which follow. i

I claim as my invention:

1. In a hole finishing apparatus having a rotatably supported, elongated, generally cylindrical member, the cylindrical surface of which constitutes a hydrostatic bearing surface adapted to cooperate with a complementary surface of a hole in a workpiece for maintaining the elongated member coaxial with the hole, the elongated member having mounting means which supports a hole finishing tool near the leading end of the member, the member being connected behind its leading end to a rotatable and axially translatable hollow drive shaft through which pressurized lubricating fluid may be fed to clearance between the cooperating surfaces, wherein:

a. the hydrostatic bearing surface constituted by the cylindrical surface of the elongated member includes respective outlet restrictor edges at the leading end and trailing end of the member, whereby the concentricity of the hydrostatic bearing surface with the complementary surface of the hole during operation of the apparatus is maintained by restoring forces which are derived from lubricating fluid pressure changes at the outlet restrictor edges and imparted to the main bearing areas therebetween;

b. the hole finishing tool is a grinding wheel mounted directly adjacent the outlet restrictor edge 'atthe leading end by the mounting means, said mounting means being arranged to produce a mass imbalance I at the tool mounting region with respect to the longitudinal axis of the elongated member during rotation thereof; and c. the hollow shaft is flexible and is connected to the elongated member by a coupling capable of transmitting pressurized lubricating fluid from thedrive shaft to passageway means in the elongated member leading to respective inlet edges of the hydrostatic bearing surface associated with said outle restrictor edges thereof.

2. The combination according to claim 1, wherein the hydrostatic bearing surface is formed as an axially separated pair of cylindrical flexible membranes, each the cooperating complementary surfaces for flow through said clearance to the respective outlet restrictor edges.

3. The combination according to claim 1, wherein the mounting means includes a bushing fitted into and concentric with the leading end of the elongated cylindrical member and further includes a shaft extending F from and eccentric with the grinding wheel and fitted into the bore of the bushing, the bushing bore being eccentric with the elongated cylindrical member by an amount matching the eccentricity of the grinding wheel shaft, whereby said mass imbalance at the tool mounting region is obtained.

4. The combination according to claim ll, wherein a guide bushing is mounted on the workpiece and held rigidly thereto where the grinding wheel enters the workpiece hole, said guide bushing being adapted to hold the elongated member in strict alignment with the axis determined by the. bore surface of the guide bushing and the finished surface of the workpiece hole.

5. The combination according to claim 1, wherein the coupling which connects the hollow shaft to'the elongated member is a universal coupling.

Claims

1. In a hole finishing apparatus having a rotatably supported, elongated, generally cylindrical member, the cylindrical surface of which constitutes a hydrostatic bearing surface adapted to cooperate with a complementary surface of a hole in a workpiece for maintaining the elongated member coaxial with the hole, the elongated member having mounting means which supports a hole finishing tool near the leading end of the member, the member being connected behind its leading end to a rotatable and axially translatable hollow drive shaft through which pressurized lubricating fluid may be fed to clearance between the cooperating surfaces, wherein: a. the hydrostatic bearing surface constituted by the cylindrical surface of the elongated member includes respective outlet restrictor edges at the leading end and trailing end of the member, whereby the concentricity of the hydrostatic bearing surface with the complementary surface of the hole during operation of the apparatus is maintained by restoring forces which are derived from lubricating fluid pressure changes at the outlet restrictor edges and imparted to the main bearing areas therebetween; b. the hole finishing tool is a grinding wheel mounted directly adjacent the outlet restrictor edge at the leading end by the mounting means, said mounting means being arranged to produce a mass imbalance at the tool mounting region with respect to the longitudinal axis of the elongated member during rotation thereof; and c. the hollow shaft is flexible and is connected to the elongated member by a coupling capable of transmitting pressurized lubricating fluid from the drive shaft to passageway means in the elongated member leading to respective inlet edges of the hydrostatic bearing surface associated with said outlet restrictor edges thereof.

2. The combination according to claim 1, wherein the hydrostatic bearing surface is formed as an axially separated pair of cylindrical flexible membranes, each supported at its opposed ends by raised lands of the elongated member which leave respective spaces underlying the membranes for accommodating pressure-induced inward deformations of the membranes, a shallow annular manifold for the pressurized lubricating fluid being provided in the elongated member in the region of the axial separation of the membranes, whereby fluid received by way of the hollow shaft, coupling and passageway means can be introduced at the respective inlet edges of the membranes to the clearance between the cooperating complementary surfaces for flow through said clearance to the respective outlet restrictor edges.

3. The combination according to claim 1, wherein the mounting means includes a bushing fitted into and concentric with the leading end of the elongated cylindrical member and further includes a shaft extending from and eccentric with the grinding wheel and fitted into the bore of the bushing, the bushing bore being eccentric with the elongated cylindrical member by an amount matching the eccentricity of the grinding wheel shaft, whereby said mass imbalance at the tool mounting region is obtained.

4. The combination according to claim 1, wherein a guide bushing is mounted on the workpiece and held rigidly thereto where the grinding wheel enters the workpiece hole, said guide bushing being adapted to hold the elongated member in strict alignment with the axis determined by the bore surface of the guide bushing and the finished surface of the workpiece hole.

5. The combination according to claim 1, wherein the coupling which connects the hollow shaft to the elongated member is a universal coupling.