US1157762A - Surface-plate. - Google Patents

Description

W. C. COMMONS.

SURFACE PLATE.

' APPLICATION FILED FEB. 17. 1915.

11 Patented Oct. 26, 1915.

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WILLIAM C. COMMONS, OF WOONSOCKET, RHODE ISLAND, ASSIGNOR TO TAFT PEIRCE MANUFACTURING COMPANY, OF WOONSOCKET, RHODE ISLAND. A COR- IPOBATION OF RHODE ISLAND.

SURFACE-PLATE.

Specification of Letters Patent.

Patented @ct. 26, 31915.

To all whom it may concern:

Be it known that I, WILLIAM C. COMMONS, a citizen of the United States, and a resident of the city of Noonsocket, in the county of Providence, State of Rhode Island, have in vented new and useful Improvements in Surface-Plates, of which the following is a specification.

This invention relates broadly to tools and more particularly to precision tools in the nature of surface plates.

The principal object of this invention s to provide a surface plate of extremely rigid construction having the test surface thereon supported by members adapted to absorb and distribute any stress applied to said surface. I

A further and primary object of this 1nvention is to provide a surface plate with a test surface so constructed as to minimize A the possibility of error due to collection of foreign matter on the said surface,

A further object of this invention is to provide a surface plate with a test surface constructed of a plurality of small spaced test surfaces all of which lie in the same plane.

Another object of this invention is to pro vide a surface plate with a test surface constructed with depressions adapted to collect and receive foreign matter, such as dirt and grit which may accidentally be deposited on said'surface.

A still further object of this invention is to produce a surface plate having a test surface thereonconstructed to obviate the production of vacuums between the test surface and the work being tested thereon.

Other and further objects of this invention will in part be obvious and will in part be pointed out hereinafter byreference to the accompanying drawings wherein like characters are used to represent like parts throughout the several figures thereof.

Figure 1 is a plan view. Fig. 2 is an elevational view showing a portion of the device in section. Fig. 3 is a small detail view illustrating a small section through the test surface. Fig. ?l is a plan view looking at the bottom of the device.

Surface plates are old and well known devices used in precision tool work, and are usually constructed with surfaces which are scraped to lie in substantially a single plane.

These surfaces as heretofore produced are usually of relatively large area. In the use of such surface plates it is customary to coat the plate with a very thin layer of red lead or some oily substance and apply the work to be tested to the coated surface. Where the work face being tested has a rela tively large area, the application of the work face against the test surface expels substantially all of the air between the two surfaces. Any attempt to separate the surfaces has the effect of producing a vacuum and the surfaces are held together by atmospheric pressure. It will be seen that where the surfaces are relatively large the effective atmospheric pressure is considerable, and consequently the test surface of a surface plate is often injured in attempting to remove tested work from the said surface. In the surface plates heretofore produced, having large test areas, it was necessary to carry grit or dirt which might lodge in the center of the plate entirely to the edge of the plate before it could be removed from the test surface. As these test surfaces are substantially true planes it will be seen that the continual wiping of grit and dirt across the surfaces will in time appreciably affect their accuracy.

The present invention which will hereinafter be described by reference to the drawings, includes a surface plate having a relatively large test surface composed of a great number of small surfaces separated by depressions or grooves. It will immediately be seen that these grooves at all times admit atmospheric pressure between the work and the general area of the testsurface thereby obviating the liability of sticking due to atmospheric pressure. It also breaks up the test surface into small areas and thereby substantially obviates adhesion. It will also be seen that by having the test surface made up of relatively small areas separated by grooves that any particles of dust or dirt need only be carried a very short distance before they are disposed of, by lodging in one of the grooves. This type of surface plate therefore is extremely accurate, due to the elimination of possible errors from the causes specified, and is very durable and not liable to injury due to sticking. Furthermore, the surface plate forming the subject of the present invention includes a relatively thick plate of metal idity for the least amount of metal.

Referring now more particularly to the drawings, the bed plate 1 is provided with an accurately formed test surface 2. This surface may be formed by grinding, lapping, or any other well known method of producing accurate surfaces. This test sur face is cut by a plurality of intersecting grooves 42 thereby dividing the general surface 2 into a multitude of small surfaces 5. These small surfaces all lie in the same plane, and therefore effectively cooperate in such manner as'to be equally as useful as a test plane as if the grooves a were absent. As has been previously explained, the grooves 4i obviate sticking and afford lodging places for foreign matter, thereby minimizing the possibility of error due to these two causes and also increasing the effective life of the test surface; Since the use of the test surface necessarily demands that it be supported so that it will not tend to bend or twist when in use, the present in vention includes a very rigid backing or support which comprises a pair of large intersecting triangles A and B arranged so that the apex of triangle A substantially bisects the triangle B, and vice versa. A web C joins the intersection of the sides of the triangles A and B, thereby forming substantially six small nested triangles 6. In order to take advantage of the cantaliver effect in securing rigidity and absorption of stresses, the major triangles A and B are slightly smaller in their dimensions than is the area of the bed plate 1, and the overhanging parts of said bed plate are supported at the ends by brackets 7 extending substantially parallel to the length of the bed plate, and the sides are also supported by brackets 8 extending substantially transverse of the bed plate. In order to produce an even primary support for said plate, supporting feet 9 are preferably formed at each angle of the triangle B thereby providing a three point suspension or support for Copies of this patent may be obtained for the plate to be carried upon. Bosses 10 are formed adjacent the meeting of the central bracket 7 and the bed plate 1, and preferably are threaded to receive the lifter bolts or handles 11, which may be used in lifting the plate where the work is of such a nature that it is difficult to bring the work to the plate, in which case the plate is lifted and applied to the work surface.

By reference to Fig. 2 it will be noted that the webs are thinner in substantially the transverse middle portion of the supporting members, and this construction is of utility for two reasons; first, the base webs of the triangles A and B act substantially as cantalivers so that for supporting purposes the metal may be lessened at the middle of the webs, and secondly this construction permits of a free air circulation beneath the bed plate and the supporting members thus i11- suring the plate to be subjected to substantially the same temperature conditions on all sides thereof. This feature is of considerable importance, as on relatively large surface plates, unequal heating may have a tendency to very slightly warp or bend the plate thus introducing an error which may be appreciable in extremely accurate work.

Having thus described my invention'what I desire to claim is 1-- 1. As an article ofmanufacture, a surface plate having the test surface thereof crossed by a plurality of grooves.

2. As an article of manufacture, a surface plate having the test surface thereof crossed by a plurality of intersecting grooves to divide said test surface into a plurality of individualized areas.

3. As an article of manufacture, a surface plate having a test surface provided with a plurality of depressions adapted to collect and receive grit and dirt.

4. As an article of manufacture, a surface plate having the test surface thereof crossed by a plurality of intersecting straight line grooves.

WILLIAM G. COMMONS.

Washington, I). C.-

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