US3918695A

US3918695A - Clamp for precision cutting tool

Info

Publication number: US3918695A
Application number: US464474A
Authority: US
Inventors: John W Baker
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-07-20
Filing date: 1974-04-26
Publication date: 1975-11-11
Anticipated expiration: 1992-11-11

Abstract

Apparatus for precision cutting of sheet material (e.g. nonferrous metals such as aluminum, brass, asbestos board, or the like), comprising a work-support table, displacement-sensing means mounted along two adjacent sides of said support table and a novel quick-clamping means for holding a workpiece against said table. The quick-clamping means has an elongate clamp bar along each side of the cutting tool, these elongate bars comprising biased means therealong for compensating for differences in thickness along the length of said workpiece.

Description

United States Patent Baker 5] Nov. 11, 1975 [5 1 CLAMP FOR PRECISION CUTTING TOOL 2.506.436 5/1950 Seybold 269/32 '7 '7 Inventor: J n w. a 4 achusetts Dri e, 3.199.860 8/1965 Moherg -69/87...

' west Acton Mass' 0171) Primur E.\'an1inerRoy Lake [22] Filed: Apr. 26, 1974 Assistant E\'uminer- -Mark S. Bicks Attornev. Agent, or Firm-Robert A. Cesari; John F. 21 A l. N 7 L l 1 PP O 464 4 4 McKenna; Andrew F. Kehoe Related US. Application Data [62] lgh'isionn of Ser. No. 273385. July 20. 1972. Pat. No. [57] ABSTRACT Apparatus for precision cutting of sheet material (e.g. U S Cl 269/87 769/366 nonferrous metals such as aluminum, brass, asbestos m g board, or the like), comprising a work-support table. [58] Fie'ld 163 265 displacement-sensing means mounted along two adja- "769/766' i, 5 cent sides of said support table and a novel quickclamping means for holding a workpiece against said ble. The quick-clamping means has an elongate [56] References Cited clamp bar along each side of the cutting tool, these UNITED STATES PATENTS elongate bars comprising biased means therealong for 816.529 3/1906 Burt 269/872 mpensating for differences in thickness alongthe l.5l9.2 5 l2/l924 Tnvns d 269/265 l.942.728 l/l934 Perlsteiil 269/275 length of Sam workplece. 2.166.998 7/1939 Morgan 269/32 7 Claims, 9 Drawing Figures l r- I l E Z: SG

Sheet 1 of 3 US. Patent Nov. 11, 1975 US. Patent Nov. 11, 1975 Sheet 2 013 if 111 I *1 v 7 US. Patent Nov. 11, 1975 Sheet3of3 Fig.3.

CLAMP FOR PRECISION CUTTING TOOL This is a co-pending divisional application divided out of U.S. Ser. No. 273,385 filed on July 20,1972 now U.S. Pat. No. 3,820,233. The copending divisional application is U.S. Ser. No. 464,475 filed on Apr. 26, 1974.

BACKGROUND OF THE INVENTION This invention relates to apparatus useful for rapidly cutting sheet material to a high precision tolerance by utilizing dimension-monitoring sensors associated with a work table and a quickly-actuatable clamp means for holding the workpiece againstthe table firmly enough, and with sufficient speed and convenience, to make the aforesaid precision attainable at practical production rates.

There has long been a problem in achieving cutting of non-ferrous sheet material to precision tolerances. By precision tolerances is meant a tolerance of plus-orminus 0.005 inch but especially of plus-or-minus 0.002 inch or better. Such tolerances are, of course, known to be obtainable in machining such non-ferrous materials as aluminum sheet, asbestos board, and the like. Nevertheless, the apparatus heretofore available for such precision cutting has not been feasible for use in many cutting jobs because of the ineffective use of conventional clamp means. The clamp means heretofore utilized have either allowed slippage which rendered the cutting process imprecise or have taken so much time to operate that any economic advantage of obtaining high precision cutting was restricted to processing a relatively high-priced work product. Consequently jobbers in the cutting of non-ferrous materials have not been able to deliver a high-precision product at a desirably low price. This general problem is particularly evident with respect to relatively small orders of highprecision sheet material.

Heretofore unrelated art concerns the finish of a sawcut edge and how quickly that finish is likely to deteriorate with prolonged use of prior art saw teeth. In general, applicants ability to produce precision-cut nonferrous articles will be understood to allow a customer to avoid any post-cutting machining operations on these articles. The precision-machined part will be ready for use as delivered. In many situations, however, the part will be subjected to a surface treatment, say anodizing, or the like and will require a good finish, say a finish of 63 root mean square (rms) or below. Presently-available saws which will provide this finish initially will provide a deteriorating result with time; that is after a days operation the finish of the cut edge may be as high as 100 rms or more. This obviously presents a problem to manufacturers who wish to produce an excellently finished, precision-cut workpiece without excessive blade-changing or post-cutting buffing steps.

SUMMARY OF THE INVENTION Therefore it is an object of the invention to provide improved apparatus for precision cutting of sheet material.

Another object of the invention is to provide apparatus comprising novel clamp means for holding a workpiece being subjected to a precise cutting operation.

Further objects of the invention are to provide a novel clamp means which is readily clamped and unclamped, to provide a novel clamp means which engages snugly the workpiece even though the workpiece itself comprises dimensional irregularities, and to provide a clamp means which successfully clamps the workpiece against movement induced or allowed by the cutting of the workpiece.

Still another object of the invention is to provide a saw which complements the high precision cutting operation by allowing the operation to produce articles having a superior finish on cut edges thereof.

A further object of the invention is to provide improved means for advancing the workpiece to be cut.

Another object of the invention is to provide a novel and relatively inexpensive means for accurately advancing the workpiece into the cutting path of the saw.

Other objects of the invention will be obvious to those skilled in the art on reading the instant application.

The invention relates to a cutting apparatus having a work table, two adjacent perimeters of which are bordered by workpiece guide rails equipped with means for sensing the proximity of the workpiece to the guide rail at a plurality of positions therealong and, consequently, allowing a quick determination of the square ness (or any predetermined angle) of a piece to be cut and also allowing a means for detecting any drift of positioning during the cutting operation. A workpiece clamp means comprising elongate clamp members closely spaced, one along each side of a cutting means and adapted to clamp the workpiece against the work table, is an important feature of the invention.

In the most favorable forms of the invention, the clamp bars comprise biasing means associated therewith whereby gaps which would ordinarily prevent snug, clampingcontact with the clamp bar are bridged by the biasing means. Thus the biasing means is advantageously an active" means in that it depends from, and contacts the workpiece below, the normal clamping surface of the clamp bar. Moreover, in the most favorable embodiments of the invention, a plurality of biasing means are arranged, not only along the direction of the cut for a distance which is substantially coextensive with the travel path of the cutting means, but also at right angles to the cut, i.e. on both sides of the travel path of the cutting means.

The actuation means for the clamp should be adapted to provide a variable clearance between work table and the clamp. This is best achieved by mounting the clamp for vertical movement and moving it by hydraulic means, mounted beneath the work table, and through a pair of ball bushings mounted proximate each end of the clamp. The clamp actuator is a constant pressure device.

Non ferrous sheet material can be finished to excellent tolerance on the apparatus of the invention. Indeed, even where tolerances of plus-or-minus 0.002 inch are required, say on a nominal /s-inch thick aluminum sheet, the apparatus can quickly and efficiently be used to turn out the sheet.

In order to give the cut edge of such a sheet a more finished" appearance, applicant has also constructed a saw means useful with the apparatus of the invention. In this improvement, finishing teeth comprising narrow flat bands, substantially vertical (i.e. radial) and tapered from the front face to the back face of the tooth, have been found to yield a finish along a cut edge which can be used suitably in a wide variety of applications without further finishing operations. The finish attainable with this saw is markedly superior both with respect to the finish initially obtainable and with respect to the rate of deterioration of the finish of the cut edge of the workpiece with use of the saw. For example, the

cut edge will have a finish of as low as 16 rms initially and is usually in the 30 rms range for non-ferrous metals such as aluminum and its common alloys. More importantly, an initially attained finish of, say 24 rms will not deteriorate substantially during the same period when use of a similar saw, not comprising the finishing tooth modification disclosed herein, would result in a deterioration of from 63 rms to about 120 rms.

Without being bound by the hypothesis, it is believed by the inventor that the advantage of his saw is the use ofa friction inducing surface which is substantially par allel along the radius of the saw blade to the workpiece edge being cut. The work created by this frictional contact of the surface is believed to have a substantial effect on smoothing the surface.

As will be further explained below, the high tolerance work achieved by the apparatus of the invention requires an even advance of the workpiece to the desired position along the linear cutting path of the saw blade. This advance has been achieved by mounting an adjustable rail for movement on two ball screw advance devices, wherein the ball screws are selected to have a close relative tolerance one to the other. Although it has been the custom in the mechanical arts to use screws machined to a particular tolerance in such situations, the inventor has discovered that standard ball bearing screws can be utilized at a great savings in cost. This is achieved by making both advance ball screws by cutting them from a single screw stock, preferable discarding several inches from the end of each such single screw. The resulting pair of screws will have veryhigh relative tolerance despite the fact the manufacturers absolute tolerance would forbid the indiscriminate use of any two separate commercially-obtained screws. Thus instead of using ground ball screws with tolerances such as 0.0005 inches per foot, applicant can use a thread rolled ball screw with a tolerance of 0.001 inch per inch. This procedure saves several hundreds of dollars in manufacturing each machine.

ILLUSTRATIVE EXAMPLE OF THE INVENTION In this application and accompanying drawings there is shown and described a preferred embodiment of the invention and suggest various alternatives and modifications thereof, but it is to be understood that these are not intended to be exhaustive and that other changes and modifications can be made within the scope of the invention. These suggestions herein are selected and included for purposes of illustration in order that others skilled in the art will more fully understand the invention and the principles thereof and will be able to modify it and embody it in a variety of forms, each as may be best suited in the condition of a particular case.

IN THE DRAWINGS FIG. 1 is a perspective view ofa cutting machine constructed according to the invention.

FIG. 2 is a fragmentary plan view of a machine similar to that shown in FIG. 1 and showing the work table and saw-travel path.

FIG. 3 is a side view of the work table and clamp actuating device as viewed along the line 3-3 of FIG. 2.

F 4 is a view of the work table and clampactuating mechanism as viewed along the line 4-4 of FIG. 5A is a fragment of the clamp bar of Fl 5 showing more detail thereof. 1

FIGS. 6 and 7 diagrammatically illustrate a novel finishing saw useful with the apparatus of the invention. 1 FIG. 8 shows the construction of a saw-guard and how it co-operates with the movementof verticallyadjustable clamping means.

Referring toFIG. 1, it is seen that cutting machine 12 is mounted on frame 14 and comprises a work table 16 and a hood-enclosed saw 18 adapted for movement with saw drive motor 19 across work table 16 on ball bushings 21 along support rods 20. Rods are typically constructed of steel 2 inches in diameter and supported on brackets 22 attached to frame 14. Also attached to frame 14 is an electric control box 24. Progress of saw 18 across the work table is dependent on the speed at which feed screw 25 is turned by a variable drive feed screw motor not shown on the drawings.

Mounted proximate work table 16 are two workpiece. positioning rails mounted at a right angle to one another. Adjustable positioning rail is mounted on ball screws 32 by means of brackets 39 and in guide member 33 for controlled movement of rail 30 against a workpiece (not shown on the drawing, but understood by those skilled in the art to rest on slats 34 and slats 35 of table 16. See FIG. 4 for the position of slats 35.). Stationary positioning rail 31 is mounted along one edge of table 16 at a right angle to rail 30. Ball screws I and a dial 42. Probes 40 are positioned to engage.

the edge of a workpiece when it is flat against the

rails

30 and 31. Sensing probes 40 conveniently extend about 0.020 inches from

rails

30 and 31 when in normal position. The dial indicator is. conveniently calibrated to a 0.020 inch scale per revolution.

A clamp bar 50, best seen in FIGS. '5 and 5A, extends across table 16. Clamp bar comprises two elongate clamping members 52, one on each side of the path of travel 54 of the cutting means, saw 18. Each clamp bar 52 comprises a plurality of independent biasing means, i.e. springs 56, mounted in receptacles 58 within clamp bars 52. Springs 56 are affixed with epoxy adhesive 58- at one end thereof.

Each clamping member 52 comprises an elongate recess 62 which provides clearance for saw guide means.

as it travels along clamp bar 52. The clamping member is preferably unitary, that is integrated into a single structural unit as is shown in FIG; 5. One spring biasing means suitable for many purposes would be a steel spring constructed of 0.094 wire, 1 inch long, 0.5 inch in diameter and exerting about 15 pounds force when compressed about 0.050 inches by clamping means shown in FIGS. 3 and 4.

Clamping member 52 is actuated for vertical clamping movement by means of bracket 68 and a flanged cartridge i.e. collar, 69. Clamp-actuation assembly 66 connected between clamp bar and ball bushing shaft 72 via a vertically slideablc ball bushing post member 73 which is snugly clamped between members 52.

Shaft 72 comprises cam rollers 74 at either end thereof; these fitting into a slot at 71in'meinber 73 so that they may turn freely. Shaft 72 is, in turn, connected via a lever arm member 76 to a pivot shaft 78. Lever arm 76 comprises, is welded to operating shaft 72 and pivot shaft 78 respectively. Shaft 78 is pivotally mounted in collars 69. Force is applied to arms 76 via shaft piston rod 80 of hydraulic cylinder 82 acting through clevis-type connector 84. Cylinder 82 is pivotally mounted at pivot 86.

In FIG. 8 is illustrated schematically one means whereby a saw housing 88 is made to accomodate the movement of clamping member 50. Two moveable side shields 90 are held in slots 92 and move freely up and down therein in response to the vertical movement of member 50.

FIGS. 6 and 7 illustrate, somewhat schematically, cutting means which is particularly useful with the apparatus of the invention. In FIG. 6, a rotary saw is mounted for rotation by motor 19 on the shaft 102 of cutting machine 12. The saw is carbide tipped and of a generally conventional design, i.e. it has roughing teeth 104 and finishing teeth 106 alternately arranged along the periphery thereof. Only a few teeth are shown in FIG. 6, this being sufficient to illustrate this aspect of the invention. Roughing teeth 104 rise somewhat higher from the outer circumference 108 of the circular portion of saw 100. These roughing teeth '104 are of conventional design. 7

The particular improvement of the inventor is related to the use in conjunction with said roughing teeth, of novel finishing teeth. As indicated in FIG. 7, finishing tooth 106 comprises a generally tapered member 110, the taper being such that angles 111 are about 3 to 5, although they may be from 1 to 10 depending upon the relative properties of the saw and the material to be cut. Along the top of each lateral faces 1 12 proximate top face 114 is a substantially vertical levelled face 115 defined by two edges 116. These faces 115 run the full length of finishing tooth 106, i.e. about 0.35 inches, and are about 0.030 inches in width. The faces are advantageously between 0.1 and 0.01 inches in width. These dimensions are particularly suited for cutting of such non-ferrous metals as alluminum.

In operation, or the apparatus, a workpieceis placed on worktable 16 and brought snugly against

rails

30 and 31. This, of course, assumes a generally rectangular workpiece since the angle between

rails

30 and 31 is a 90 angle in the illustrative example of the drawings. Assuming all indicators are properly calibrated and the angle of the workpiece is perfectly square, all indicator dials will read the same. However, to the extent that the workpiece is out of square or has other defects like sizeable burrs, they immediately become evident. Thus the piece can be squared" before proceeding further or, if a single side is imperfect, the fault side can be selected to be the side removed during the cutting operation.

Once the operator is assured the workpiece is in condition to proceed, and in the proper position relative to saw path 54, he causes cylinder 82 to retract about 2 inches and thereby causes arm 76 to pivot down. Thereupon clamp bar 50 bears down on the workpiece on each side of travel path 54. The workpiece is supported on slats 35,-the saw travelling between such slats as seen in FIG. 2.

Springs 56 are typically placed about l-inch apart along, say, a 20-inch length of the clamp bar. If just compressed to the edge of their housings, these springs will exert a minimum of about 600 pounds of pressure. Normally, however, the clamping pressure will exceed this considerably and the only springs that will be effective in the clamping action will be those which protrude outside of receptacles 58 to engage a surface which, for some reason, doesnot contact a main bearing surface of clamp bar 50. i

When the workpiece is properly clamped, the sawing can be carried out, and the proper positioning of the workpiece can be visually monitored as the sawing progresses.

Among the modifications which can be made in the illustrated apparatus is the substitution of various elongate biasing means for one or both of the illustrated series of springs. One' desirable substitute would be an elongate strip or elastomeric material, e.g. a distortable synthetic rubber such as chloroprenega nitrile rubber, or an elastomeric silicone resin material. Such a strip would have the advantage of being in continual contact along the portion of the workpiece being processed. Another useful biasing means is a fluid containing balloon which could be expanded by the use of either water or gas to achieve the desirable clamp pressure on portions of the workpiece that do not fit snugly against the main bearing surface of the clamp bar.

It will be understood that a single clamp bar can comprise one or more such biasing means.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

I claim:

1. A clamp for holding a workpiece firmly against a work table and thereby to enable the precision cutting of said workpiece, said clamp comprising A. two elongate clamp members defining a slot between said clamp members said slot adapted to form a travel path for a cutting tool;

B. A plurality of downwardly extending biasing means arranged along the length of each said clamp member, said biasing means adapted to provide means for biasing said clamp and said workpiece to assure clamping contact of said workpiece against said work table;

C. means to raise said clamp vertically from said work table to provide a variable clearance between said table and said clamp, and

D. means to maintain substantially constant clamping pressure on said clamp at variable clearances from said table.

2. Apparatus as defined in claim 1 wherein said biasing means exert a minimum of 600 psig.

3. A clamping apparatus as described in claim 1 comprising additionally a saw housing comprising two moveable side shields adapted to be moved freely up and down in response to the vertical movement of said clamp.

4. A clamp as defined in claim 1 wherein said means for raising and lowering said clamp members with respect to said table are actuated by force applied proximate to each end of said clamp members, and wherein said means for raising and lowering said clamp mem-' bets comprise:

a. post members connected to said clamp members proximate to each end thereof, each of said post members comprising a slot therein,

b. ball bushings mounted on said table and forming means to receive, for slideable vertical movement therein, each of said post members,

0. means to vertically move said post members thereby, adapting said clamp members to clamp and unelamp said object and wherein,

i. said means to vertically move said post comprising l. lever means and 2. cam rollers positioned for rotation in said slots of said post, said cam rollers, forming means to transmit force to said post members on actuation of said lever means.

5. Apparatus as defined in claim 1 wherein said .biasing means comprise a series of apertures, each having a spring connected within, each spring normally protruding from its associated aperture, thereby providing a biasing means which has no substantial effect when said springs are compressed into said apertures,

6. Apparatus as defined in claim 5, wherein said biasing means exert a minimum of 600 psig.

7. A clamp as defined claim 5 wherein said means for raising and lowering said clamp members with respect to said table are actuated by force applied proxi: mate to each end of said clamp members, and wherein said means for raising and lowering said clampmeans comprise: v I I a. post memberscpnnected to said clamp members proximate each end thereof, each of said post .members comprising a slot therein,

therein, each of said postmembers, c. means to vertically move said post members thereby, adapting said clamp members to clamp,-

and unclamp said object and wherein,

i. said means to vertically move said post comprise ing 1. lever means and 2. cam rollers positioned for rotation in said slots of said post, said cam rollers forming meansto transmit force to said post members on actua-

Claims

1. A clamp for holding a workpiece firmly against a work table and thereby to enable the precision cutting of said workpiece, said clamp comprising A. two elongate clamp members defining a slot between said clamp members said slot adapted to form a travel path for a cutting tool; B. A plurality of downwardly extending biasing means arranged along the length of each said clamp member, said biasing means adapted to provide means for biasing said clamp and said workpiece to assure clamping contact of said workpiece against said work table; C. means to raise said clamp vertically from said work table to provide a variable clearance between said table and said clamp, and D. means to maintain substantially constant clamping pressure on said clamp at variable clearances from said table.

2. cam rollers positioned for rotation in said slots of said post, said cam rollers forming means to transmit force to said post members on actuation of said lever means.

2. cam rollers positioned for rotation in said slots of said post, said cam rollers, forming means to transmit force to said post members on actuation of said lever means.

4. A clamp as defined in claim 1 wherein said means for raising and lowering said clamp members with respect to said table are actuated by force applied proximate to each end of said clamp members, and wherein said means for raising and lowering said clamp members comprise: a. post members connected to said clamp members proximate to each end thereof, each of said post members comprising a slot therein, b. ball bushings mounted on said table and forming means to receive, for slideable vertical movement therein, each of said post members, c. means to vertically move said post members thereby, adapting said clamp members to clamp and unclamp said object and wherein, i. said means to vertically move said post comprising

5. Apparatus as defined in claim 1 wherein said biasing means comprise a series of apertures, each having a spring connected within, each spring normally protruding from its associated aperture, thereby providing a biasing means which has no substantial effect when said springs are compressed into said apertures.

7. A clamp as defined in claim 5 wherein said means for raising and lowering said clamp members with respect to said table are actuated by force applied proximate to each end of said clamp members, and wherein said means for raising and lowering said clamp means comprise: a. post members connected to said clamp members proximate each end thereof, each of said post members comprising a slot therein, b. ball bushings mounted on said table and forming means to receive, for slideable vertical movement therein, each of said post members, c. means to vertically move said post members thereby, adapting said clamp members to clamp and unclamp said object and wherein, i. said means to vertically move said post comprising