US2734318A

US2734318A - Offen

Info

Publication number: US2734318A
Authority: US
Publication date: 1956-02-14
Anticipated expiration: 1973-02-14

Description

A. OFFEN Feb. 14. 1956 LAPS 5 Sheets-Sheet 1 Filed Jan. 1a, 1955 ,Ihvenivr. gAri/zurO/fen g m/FM Feb. 14, 1956 A. OFFEN 2,734,318

LAPS Filed Jan. 13, 1953 5 Sheets-Sheet 2 lnverzi'or. Arthur Offt'n Feb. 14, 1956 A. OFFEN 2,734,318

LAPS

Filed Jan. 13, 1953 5 Sheets-Sheet 3 In yen for.

Feb. 14, 1956 OFFEN 2,734,318

LAPS

Filed Jan. 13, 1955 5 Sheets-Sheet 4 In ran to r.

Arthur Offen Feb. 14, 1956 A. OFFEN 2,734,318

LAPS

Filed Jan. 13, 1955 5 Sheets-Sheet 5 Inventor. .Hri-huz Offen United States Patent LAPS Arthur Olien, South Nutfield, England, assignor to Arthur Often Developments Limited, London, England, a British company Application January 13, 1953, Serial No. 331,040

6 Claims. (Cl. 51--92) This invention concerns improvements relating to lapping.

The main object of the invention is to provide an improved method of, and apparatus for, internally lapping small round cylindrical holes, especially those of relatively great length.

The holes to be lapped may be as small as ,4 inch in diameter.

The invention is, however, also capable of application to the internal lapping of larger round holes and to the external lapping of round parts. The round surfaces to be lapped may be of cylindrical or of taper formation.

The present invention provides a method of lapping a round surface of a work-piece, comprising the steps of positioning a coiled lap element coaxially with the round surface, with one or more coils in contact with the round surface, and producing relative rotation of the lapelement and the work-piece about the axis of the lap element so as to produce lapping of the round surface by the coil or coils.

The method preferably includes the additional step of reciprocating the lap element and the work-piece relatively along the axis of the lap element during the lapping operation; and also, for lapping a hole, the preliminary steps of forming a coiled wire lap element made of resilient material to a diameter greater than the diameter of the hole, applying an axial tension to the lap element so as to stretch the element and thereby contract the coils to an extent suiiicient to enable the element to be passed into the hole, and reducing the axial tension on the lap element so as to increase the diameter of the coils and obtain the requisite resilient pressure of the coils against the surface of the hole for the lapping operation.

The present invention also provides a machine for carrying out the method comprising the combination of a coiled-wire lap element, a rotary support device for each end of the lap element to permit rotation of the lap element about its axis, and driving means for rotating the lap element about its axis.

The driving means may be connected to both the rotary support devices whereby the lap element is driven simultaneously from both ends; but the lap element may be driven from one end only.

The arrangement is preferably such that one at least of the rotary support devices is adapted to be displaced in the axial direction of the lap element so as to adjust the tension of that element and thereby the diameter of the lap element coils.

The rotary support device may conveniently be in the form of a chuck fitted to the spindle of a driving motor.

The driving means preferably comprises an air turbine. Very high speeds of rotation are desirable for effective lapping. Speeds of 60,000 revolutions a minute can be obtained with an air motor.

The lap element may be made from a length of stiff .resilient wire having a portion coiled to serve as a lap- 2,734,318 Patented Feb. 14, 1956 See ping surface, and the lapping surface of the coils is provided with an adherent layer of abrasive material.

The invention is illustrated by way of example in th accompanying drawings, in which: 1

Figure 1 is a front elevation of a lapping machine mounted on a stand;

Figure 2 is a side elevation of the machine and stand, with the stand and a portion of the machine base sectioned;

Figure 3 is a cross-sectional view on an enlarged scale through the middle of the head of the machine;

Figure 4 is a cross-sectional view on an enlarged scale through the middle of the base of the machine;

Figure 5 is an underside view on the line 5-5 of Figure 3;

Figure 6 is a sectional view on the line 6-6 of Figure 5;

Figure 7 is a fragmentary plan view of the blading of the turbine rotor;

Figure 8 is a view showing one way of securing an end of a lap element to a nipple;

Figure 9 is an elevation, partly in section, of a lap element mounted on a rod;

Figure 10 is a sectional View on the line 1010 of Figure 9, and

Figure 11 is an elevation of another form of lap element.

Referring first to Figures 1 to 7, there is provided a stand 10 fitted for a platform 11 on which is mounted a lapping machine 12. incorporating a base 13, a head 14, and two side columns 15, 16 connecting the head and base.

The middle of the head has a vertical bore 17 in which is slidable a cylindrical housing 18 for a rotary driving unit. As shown in Figure 3, the unit incorporates an air turbine provided with a bladed rotor 20 fixed on the top end of a vertical spindle 19. The rotor cooperates with a stator 21. On the stator is mounted a dished valve plate 22 of circular form. This valve plate is mounted for limited rotary adjustment. It is fixed on the lower end of an upstanding tube 23, whose upper end is fitted with a radial arm 24. The tube is mounted for angular movement about its axis to adjust the valve plate, being located in a stout tubular post 25 carried by' the housing 18. The post projects through a guide hole 26 in the top of the head.

Compressed air is supplied to the turbine through a; pipe line 27 to a port 28 in a nipple 30 secured to the side of the post 25. The compressed air is fed thence down the annular space 31 between the tube 23 and the inner wall of the post, passing into a chamber 32 in the top of the driving unit above the valve plate 22.

The valve plate 22 has two diametrically-opposed ports 33. By turning of the plate in one or other direction, these ports are brought opposite the inlet ends of one or other of two pairs of oblique nozzles 34, 35 in the stator (Figure 5). The nozzles 34 are so arranged as to direct jets of air in a tangential direction against the blades 29 of the rotor. arranged to direct jets of air tangentially against the backs of the blades, i. e. in the opposite direction, in order to afford a braking medium for quickly stopping the rotor.

The spindle 19 rotates in bearings 36 within a dependent neck 37 on the housing 18 of the rotary driving unit. Exhaust air from the turbine rotor passes into a chamber 38 and thence downwardly through the gap between the spindle and a sleeve 40 between which the bearings 36 are located. The exhaust air then rises up an annular duct 41 in the neck, and is discharged along radial ducts The other pair of nozzles 35 is The neck 37 is externally screw-threaded at 44 into a boss 45 having a bearing 46 in the bottom of the head. The boss forms part of a rotary sleeve 47. The rim of the sleeve is provided with a dial surface 48. On the sleeve is an adjustable ring 49 bearing a scale with a zero mark, whose position is changed by turning the ring. On turning of the dial 48, the housing 18 is moved up and down in its bore 17 by the screw-threaded connection 44. Rotation of the housing is prevented by a key 50 in the head that projects into a vertical slot 51 Within the housing.

' Fixed on the lower end of the neck 37 is a thrust bearing device 52 incorporating a shallow circular chamber 53 housing a rotary disc 54 fixed on the lower end of the spindle 19. The bottom face of the disc is of conical formation, and the opposed bottom wall is of corresponding formation. Compressed air is fed into the bottom of the chamber through a port 55 from a pipe line 56 for a purpose to be described later. There is a knife-edge leakage path at 57 between the spindle and the bottom of the bearing device. There will also be a leakage of air through the narrow clearance between the rim of the disc and the annular wall of the chamber 53.

The lower end of the. spindle 19 is screw-threaded to receive a chuck device 58 for holding the upper end of a lap element 60.

The lap element consists (Figure l) of a length of stiff resilient wire having a middle portion 61 wound to helical formation and axially-disposed ends.

In the base 13 is a vertical bore 62, aligned with the bore 17, and fitted with a vertically slidable housing 63 for a lower rotary driving unit. The rotary driving unit is an air turbine having the same form as the upper driving unit in the housing 18, and the same reference numerals are used for corresponding parts. The lower end of the lap is fixed in a chuck device 58.

The upper portion of the housing 63 projects through the top of the base, where it is fitted in an annular trough 64 for catching lubricant.

On top of the post 25 on the upper turbine housing 18 is fixed a balance valve 65 for controlling the supply of pressure air to the inlet port 55 of the thrust bearing unit 52. This valve incorporates a cylinder 66 in which is vertically slidable a piston 67. The top of the piston is engaged by a coiled return spring 68 fitted within a recess 70 in a cap 71 on top of the cylinder. A recess 72 in the bottom of the piston houses a coil compression spring 73 which bears upon the top of the tube 23 that carries the valve plate 22. An inner pipe 74 for the supply of oil mist lubricant passes centrally down the tube 23; its upper end passing through a clearance hole 75 in the middle of the piston 67, and being in communication with an inlet port 76 for the supply of oil mist under pressure. On the lower end of the oil mist tube 74 is a tubular nose 77 which is a free sliding and rotary bit in a central hole within the stator 21. In the tip of the nose is a housing for a thrust ball 78. There is a clearance in the thrust ball housing for the passage of oil mist into the turbine housing 18. The ball bears upon a thrust disc 99 on the top of the spindle 19.

The opposed walls of the piston and cylinder of the balance valve 65 are provided with co-operating

annular ducts

80, 81. The duct 81 in the cylinder is connected to a port for the supply of pressure air through the pipe 56 to the port 55 in the bearing unit. The supply of air to the port 55 is controlled by the extent of the adjustable overlap between the two

ducts

80, 81 through up-anddown movement of the piston 67. Pressure air is supplied to the annular duct in the piston through a pipe line 82 connected to a source 83 of air pressure.

A similar balance valve 84 is fitted on the bottom end of a post 35 that projects downwardly from the turbine housing 63 through the base 13 and platform 11 into the hollow stand 10. The same reference numerals are used for corresponding parts. A branch pipe 86 for the supply of oil mist from the source 83 is connected to an inlet port 76 in the bottom of the lower balance valve.

When the lap element is fitted to the machine, it is stretched so as to contract the coils. The pressure of air supplied to the thrust bearing device 52 is so adjusted as to first balance the tension of the lap. There is then no load, or but negligent load, on the rolling bearings 152.

The balance valves each act to adjust the pressure of air supply applied to the coned face of the associated thrust disc 54, in such a way that the air pressure on the disc is automatically adjusted to counterbalance any changes in pull on the spindle 19 due to changes in tension by the lap element during the lapping operation. Assuming there is an increased pull by the lap element, there will be an initial downward movement of the upper spindle 19, which carries down the thrust disc 54 and bladed rotor 20. There is a following downward movement of the inner tube 74. In consequence, the piston 67 of the balance valve 65 slides down the cylinder; and the overlap between the two

annular ports

80, 81 is increased, so increasing the supply of pressure air to the chamber 53 of the bearing unit 52, until the pull by the lap element is counterbalanced. Thus the pressure of the lap element against the surface being lapped is maintained substantially constant and an axial pressure in the machine bearings is reduced or removed. There is a corresponding adjusted compensation effect produced by the lower balance valve 84 for the lower bearing unit 52.

A lever arm 90 is pivoted under the platform 11 to the back of the stand. This arm extends forwardly, and is coupled by a link 91 to a pedal lever 92. The front edge of the pedal lever projects through a hole 93 at the front of the machine, where it is provided with a pedal 94. Near its free front end the lever arm 90 is connected by a pull rod 95 to the body of the lower balance valve 84. When the pedal 94 is depressed, the lever arm 90 is drawn down, and this movement produces a corresponding downward movement of the lower balance valve 84. The post 85 moves down with the balance valve, so drawing down the housing 63 for the lower driving unit in its bore 62. The chuck device 58 holding the end of the lap element is thereby pulled down so as to stretch the lap element and thereby contract the coils.

The forward tip of the lever arm 90 is adapted to be engaged by a stop 96 to limit upward movement of that arm. This stop is carried by a slidable handle 97 fitted with pins 98 guided in a support 100. If the pedal 94 is first pushed down, and the handle 97 pulled forward, against a return spring 101, so as to draw the stop 96 forward, the pedal can then be released so as to enable the lever arm 90 to move to a fully raised position at which tension on the lap element is relieved. The purpose of this operation will be described later.

The machine is provided with a platform or work-table 102having guides 103 at its sides which are slidably fitted on the two columns 15, 16. The work-table has a clearance hole for the lap element. Bellow-shaped gaiters 104 protect the columns and serve as ducts for oil mist. A work-piece is shown at 105 in dotted lines on the worktable. The lap element 61 shown is intended for lapping a round hole of cylindrical form in the work-piece. During the lapping operation, the work-table is moved automatically up and down so as to cause the lap element to move along the hole while the lap element is rotating. This movement of the work-table is produced by a hydraulic mechanism (shown diagrammatically) which incorporates two piston-and-cylinder devices 110. Oil is supplied under pressure alternately to the two ends of each cylinder 111 through valves 112 controlled automatically by a trip device 113 operated by stops 114 on one of two vertical piston rods 115 fixed to the sides of the worktable 102.

At the back of the machine (see Figures 2 and 3) there is a vertical tubular shaft 'mounted for rotation in a bracket 121 and a bearing 122. At its upper end the shaft is fitted with a radial arm 123 that carries a pin 124 engaged within a fork 125 at the end of the arm 24. The lower end of the shaft is fitted with a pair of parallel

radial arms

126, 127, connected by a pin 128 which engages a fork 129 on the lower arm 24. The valve plates 22 are turned to one or other of their two positions by swivelling the shaft 120 about its axis by a manual control. This control consists of an arm 160 on the shaft 120 actuated by a push-pull rod 161 that projects to the front of the machine where it is fitted with a hand knob 162.

At 130 is a vessel for supplying compressed air with oil mist through

pipe lines

131, 132 to the ports 76 in the two balance valves.

The source of air pressure 83 is connected to the bottom end of a tube 133 (see Figure 3) housed within the shaft 120. The two pipe lines 27 are connected respectively to the upper and lower ends of this tube. The two pipe lines 82 are also connected to the ends of the tube. There is a further branch pipe (not shown) for supplying pressure air to the vessel 130.

In setting up for a lapping operation, the work-table 102 is lowered, and with the upper end of the lap element 51 fixed in the upper chuck 58, the lower end of the lap element is led through the hole in the work-piece 58. The lower end of the lap element is now fixed in lower chuck 58. The pedal 94 is now depressed, so as to stretch the lap element, and thereby contract the coils, whereupon the work-table is raised in order to bring the coiled portion of the lap within the hole of the work-piece. The petal 94 can now be released to permit expansion of the lap coils against the wall of the hole. The tension is adjusted by turning the dial 48. The turbine motors can now be run to rotate the lap element about its axis for the lapping operation.

It is preferred to fit each end of the lap element with a nipple 134 as shown in Figure 8. The nipple has a shank 135 which is screwed to receive a coiled end 136 of the wire lap. The nipple is adapted to be engaged in a chuck 58.

The lap element shown in Figures 9 and is intended primarily for lapping blind holes, but it can also be used for lapping open-ended holes. A helically-wound wire lap element 140 is mounted co-axially on a rod or mandrel 141, and one wire end is fixed to a boss 142 on one end of the rod. The other end of the rod is formed with an integral boss 143, which is slotted at 144 to receive a sliding blade 145. A sleeve 146 mounted on the boss is internally screw-threaded at 147, and engages screw threads 148 on the blade. A collar 149 slidable on the rod is secured by screws 150 to the blade. The collar is connected to the adjacent end of the lap element. A thrust bearing 151 is fitted between the adjacent ends of the sleeve and boss. When the sleeve is turned, the collar slides along the rod, so adjusting the length of the lap, and thereby contracting or expanding its coils. When using this lap element only one driving unit may be used, the lap element being adjusted manually.

In Figure 11 is shown another form of lap element incorporating two

coiled wires

160, 161 arranged in the manner of a two-start thread. The

non-cutting end portions

162, 163 are coiled to a smaller diameter, and pins 164, 165 with nipples are engaged within these coiled ends, where they are secured, as by sweating or screwing. There may be three coils in the form of a threestart coil, or a greater number of coils arranged in a similar manner. The provision fo two or more coils avoids any possibility of a one-sided pull at the ends of the element which would cause the element to run out of truth. The coiling of the element along the full length also affords truer running under tension because of the increased flexibility.

In the lap element of Figures 9 and 10 an additional coiled wire may be provided as shown at 166.

The wire from which the lap is made may be of any suitable section, such as round, square, or rectangular.

6 A convenient section is a round section. This section, however, has the disadvantage that it has only a line contact with the surface of the hole. It is therefore advisable to grind or roll a flat on the coils.

In one suitable way of loading the lap element with an abrasive, the surface is coated electrolytically with a layer of copper. Some suitable abrasive material, such as diamond dust, is pressed into the coating. It is of importance that the particles shall stand proud of the coils in order to afford a working clearance for lubricant and swarf. The coils of the lap are thereafter treated electrically by a reverse process to remove a portion of the copper layer, until the diamond particles are exposed by approximately /5 to /6 of their diameter.

I claim:

1. A lapping machine comprising a lap element, which lap element comprises at least one helically-coiled, resilient wire and end members at the ends of the element connected together by the wire, said wire constituting the only connection between said end members and providing a lapping surface for the element, support devices gripping said end members, reciprocating means for effecting relative movement of the support devices in the direction of the axis of the lap element, whereby an axial tension can be applied to the lap element and its diameter thereby adjusted, supporting means for holding a work-piece to be lapped, and means for effecting relative rotation between the lamp element and the supporting means.

2. A lapping machine comprising a lap element, which lap element comprises at least one helically-coiled, resilient wire and end members at the ends of the element connected together by the wire, said wire constituting the only connection between said end members and providing a lapping surface for the element, rotary support devices gripping said end members, reciprocating means for effecting relative movement of the rotary support devices in the direction of the axis of the lap element, whereby an axial tension can be applied to the lap element and its diameter thereby adjusted, driving means for rotating the support devices, a thrust bearing for each rotary support device, which thrust bearing comprises a rotary disc-like member connected to the rotary support device for rotation therewith and pressure means for subjecting that face of the disc-like member nearer to the lap element to fluid pressure, thereby counterbalancing the axial pull of the tensioned lap element, supporting means for holding a work-piece to be lapped, and reciprocating means for moving the supporting means in an axial direction.

3. A lapping machine as claimed in claim 2 in which throttle means are provided displaceable by the pull of the lap element to regulate the fluid pressure in accordance with the pull of the lap element.

4. A method of lapping a round surface of a work-piece, comprising the steps of forming a coiled wire lap element made of resilient material and having a lapping surface with coils having a radius greater than the radius of curvature of the round surface, gripping the ends of the lap element and applying an axial tension to the lap element, positioning the lap element co-axially with the round surface, adjusting the axial tension on the lap element so that'the coils resiliently press on the round surface, and positively rotating both ends of the lap element and thereby producing relative rotation between the lap element and the work-piece.

5. A method as claimed in claim 4 in which the axial tension applied to the lap element is adjusted during said relative rotation.

6. A method of lapping a round hole in a work-piece, comprising the steps of forming a coiled wire lap element made of resilient material and having a lapping surface to a diameter greater than the diameter of the hole, gripping the ends of the lap element and applying an axial tension to the lap element so as to stretch the lap element and thereby contract the coils and reduce the diameter of the lap element to an extent suflicient to enable it to be passed into the hole, positioning the stretched lap element Within the hole, reducing the axial tension of the lap element and thereby increasing the diameter of the element so that it bears against the surface of the 1101c, and positix'ely rotating both ends of the lap element and thereby producing relative rotation between the lap element and the work-piece.

References Cited'in'the file of this patent UNITED STATES PATENTS 8 Soule July 27, Hodgkins Aug. 28, Hedeen Nov. 17, Green Oct. 9, Kennedye May 22, Stempelin Jan. 22, Johnson July 30, Sam Apr. 7,

FOREIGN PATENTS Great Britain Feb. 10, Great Britain July 25,