US2410877A - Dimension gauge - Google Patents

Description

2, w46. J. B.' HALL 24i087'7 DIMENSION GAUGE Filed Aug. 27, 194s i 2 sheets-sheet 2 Iaweazoal: da.. 6M

Patented Nov. 12, 1946 DIMENSION GAUGE JohnB. Hall, Wakefield, Mass.,v assignor of onehalf to Frank I. Hardy, Boston, Mass.

Application August 27, 1943, Serial No., 500,269

3 Claims.

This invention relates to improvements in tools and more especially to improvements in gauges of the type employed in making precision measurements whereby mechanical parts are brought into close conformance with accepted standards;

Examples of precision tools of the character rem ferred to are surface plates, snap gauges, plug gauges, angle irons, pedestals, and many others. Thesetools are customarily made of metal, a ma,- terial which is subject to the development of. lnaccuracies` from Various causes. For instance, metal develops dimensional instability upon exposure to iiuctuating temperature conditions. Similarly, metal is subject to minute distortion or flexing from pressure conditions developing externally of the metal, as by a. weight applied thereon, and also internally of the metal from stresses and strains within the metal itself. Gauges of metal are further subject to Wear which likewise causes inaccuracies. In the case of some of these tools, as for instance surface plates,` it is necessary t provide relatively large surfaces nnished to a line tolerance. Such surfaces cannot be accurately formed by conventional grinding operationsand as a result, hand scraping operations are necessary which require considerable time and' greatly increase the cost of the tool.

An object of the invention is to improve tools used in making precision measurements and to devise means for overcoming er substantially reducing the various difliculties above noted. a further object of the invention to. provide irnproved gauges which are characterized by cheap.- ness, durability, and more ecient operation.

The nature of the invention and its objeetswill.

be more fully understood from the following. de-

scription of the drawings, and discussion relating.

thereto.

In the accompanying drawings:

Fig. l is a perspective view illustrating a surface plate of the invention;

Fig. 2 is a cross section taken on the line 2-2 of Fig. 1;

Fig. 3 is an enlarged detailed view of the surface plate illustrating a ground surface;

Fig. 4 is a perspective View illustrating a modi-V It isv selvesto formation into various types of precision tools, inV which form the rocks provide various advantages in comparison with metal. Examples of materials suitable for this purpose are the igneous rocks, suchas granite, gabbro, diorite, dabase, basalt, trap, rhyolite, and others.

Theterm igneous rock as employed in geology ief'ersto a class-'of substances which were formed by heat beneath the earths crust and forced to thel surface by pressure, thereafter forming an extremely hard mass through a period of slow cooling and seasoning. Igneous rock of the class represented by the above indicated group of rocks, du@ tov slow cooling and seasoning processes, is substantially free from stresses and strains such are sometimes encountered in metal, is substantially unaffected by temperature changes, and is highly incompressible. Igneous rock is distinguished fromK sedimentary rock by the fact that the latter substance is formed by deposits in thelabsence of heat.

There occur in nature several'types of granite which are, further classied as biotites, hornblend, biotite-muscovite, and quartz-monzonite, andthe like. Ofthese; the largest number of so-Called commercial granites. utilized in connection wit the invention, are biotites.

Referring more in, detail to the application of igneous rock to precision tools, I have disclosed in Fig. l' a preferred embodiment of the invention, consisting of a surface plate I which is composed entirely of a granite such as biotite. The surface plateco-nsists of a flat slab of the granite. To facilitate handling, the granite may, if desired, be formed with rib portions 2 and with a flange or overhanging, edge 3 constituting an extension ofthe workingV surface il. The surface 4 presents a grain formation made up of tiny peaks 5 and.

pits or depressions 6.

characteristic of the granites is a well-dened grainV formation which may be visualized as resulting from multiplicity of tiny flat particles piled one upon another in a definite pattern of straight lines. Cleavage of the rock across. the particles forms a definite grain surface, which is commonly, referred. to as the head grain, and a surface` formed b y cleaving a granite body across its particles includes the characteristic heads 5 and pits 5, illustrated in Fig. 3 of the drawings.

The importance of the grained surface l of the plate l is best understood from a consideration of thek requirements of a conventional surface plate; Such tools are generally utilized to provide an extremely accurate supporting surface for assembling work which must be finished to close tolerance (.0001-.0005). Such a requirement calls for an exceedingly smoothly finished surface which, in the case of metal, may reduce slidability. In the case of a surface plate especially, it is desired to maintain slidability at the surface so that work may be easily adjusted and will not freeze thereon. To prevent such freezing while still maintaining ne tolerance, it is customary to hand scrape a metal surface and form therein minute depressions which serve to prevent freezing.

The grained surface 4 of the granite surface plate of the invention is especially desirable from the slidability point of view since by reason of the tiny pits E occurring between the heads 5, an interrupted surface is always provided for and "freezing is automatically avoided.

In place of the hand scraping operation commonly carried out on metal, the present plate is surfaced by a grinding operation, utilizing granite surfaces which are applied to the surface tc be ground, in conjunction with the use of a fine abrasive such as carborundum. While the surface 4 is preferably formed from cleaving the granite across the grain to expose the head grain in the manner described, it may nevertheless be desired, for some types of tools, to utilize the granite with the grain running in other directions than at right angles to the plane of the surface of the plate.

Formation of a metal surface by hand scraping operations is a diicult and time-consuming operation, made necessary by reason of the fact that metal grinding equipment cannot be used on account of deflection or distortion developing in the grinding members. In the case of the granite plate, however, surface grinding operations may be successfully carried out by the use of granite grinding members which are not subject to deflection or other dimensional instability.

Grinding may be carried out by reciprocating movement of a granite block on a plate surface, making use of abrasive such as carborundum, or by grinding with a granite wheel, or in other ways. One immediate result obtained from this ability of granite to serve as a grinding member as Well as to be formed by grinding, is that close tolerances can be carried out on relatively large sized plates, whereas it is practically impossible to conform to standard tolerances by hand scraping of metal in the larger sizes of surface plates. For example, a tolerance of .0001 of an inch is commonly specified for a 12 square metal plate, while a 24" square plate can only beground to .0002 tolerance and so on, with larger sizes being limited to tolerances of .001 or greater. With the plate of the invention, a .0001 tolerance can be maintained throughout the surface of large size plates.

In use, the granite surface plate exhibits several unusual properties. It is substantially free from dimensional changes in the presence of fluctuating temperatures, and it is believed that if any change whatever does take place from changing temperature conditions, it does so in a very uniform manner, with the result that no irregularities develop in the surface 4 of the plate. This resistance of the granite to temperature changes is thought to be due in part to the fact that it is of a highly impermeable and seasoned character and that it only very slowly accepts or releases heat. Because of this dimensional stability it is possible to provide standard gauge members, in

various sizes, which may be used in a wide range of temperatures without significant variation ln tolerance.

A common feature of metal surface plates is a reinforcing construction consisting of a number of ribs disposed at the under side of the metal surface plate and running in various directions to offset any deflection in the plate from pressure conditions. Such deflection is generally recognized as being due to a slight resiliency present in metals, especially those which may include stresses and strains.

The matter of deection in the case of the granite surface plate of the invention does not arise since there is substantially no resilience whatever in the granite and it develops no tendency to flex under any pressure conditions, due to its highly incompressible mass formed under heat and pressure and subsequent slow cooling by natural processes.

The tendency of metal surface plates to Wear, results in the need for frequent correction and resurfacing operations of expensive character. This problem of Wear is greatly minimized by the use of granite as the latter material successfully withstands usage with a highly developed resistance to wear which has not been fully determined but which is understood to greatly reduce resurfacing operations, and in some cases to eliminate resurfacing throughout the life of the tool.

The surface plate of the invention is characterized by various other advantages such as being rust and corrosion resistant, and hence does not require applications of oil or grease to protect the finished surface. The surface itself can be renished in less time and at less cost than is the case with metal. The finished granite surface when damaged will not raise burred edges, which might scratch or mar lapped metal surfaces applied thereon. Instead of raising burred edges, the surface plate merely chips away, leaving only a depression.

The dimensional stability of granite and other i igneous rocks furnishes a basis for a desirable modification of the conventional form of surface plate. Such a modification has been illustrated in Fig. 4. I have chosen to designate the modification as a table gauge. This gauge includes a base 'l consisting of a granite surface plate corresponding in all respects to the surface plate I illustrated in Fig. 1. Mounted on the base 'l is an upright frame member 8, also composed of an igneous rock such as granite, and preferably formed with a side surface 9 which extends at right angles to the plane of the surface l0 on the surface plate 1, thus to provide a second vertical gauge surface of equal dimensional stability and ne tolerance. In addition, the frame has a top anvil portion Il, with still a third gauging surface I2 formed at the under side thereof, which lies in a plane parallel with the surface I0. The distance between the surfaces is carefully ground to a standard, thus to provide in effect a greatly enlarged snap gauge which includes a surface plate of a size adapted for large scale work.

The modification illustrated by Fig.. 4 may further include an angle iron member i3, having still another gauging surface B4 which extends at right angles to the plane of the surface l0 and parallel with the surface 9 of the upright frame 8. The angle iron i3 is illustrative of various other gauging tools which may be desired to be utilized on the surface plate l, in conjunction with the upright 8, and affords a means of carrying out various gauging operations, all of which may be free from dimensional instability irrespective of temperature changes and other conditions.

Preferably the entire body of the upright frame 3 is formed of granite in order to resist any inaccuracies from temperature fluctuations. It may, however, be desired to form a part only of the upright of granite, with some other material utilized for the remainder of the tool. Various other arrangements may be resorted to which utilize the property of the granite of being free from dimensional instability.

A further modication of the invention has been illustrated in Figs. 5 and 6, which disclose a straight edge member l5 also formed of an igneous rock such as granite, and including a straight edge surface I6, a rib portion I 1, and pedestals I8, with the rib portion I1 further being formed with openings I9. This tool conforms in all respects to the shape and style of a metal straight edge but is characterized by the properties inherent in igneous rock as already set forth in connection with previous modications. Various other applications of igneous rock may also be resorted to in accordance With the invention, a-s for example in making ring gauges, plug gauges, buttons and anvils for snap gauges, and others. Any of the Various igneous rocks as a1- ready referred to may be employed in this con nection.

From the foregoing, it will be seen that I have eiected substantial improvements in gauges by means of which closer tolerance may be obtained, better resistance to wear is possible, freedom from substantially all dimensional instability is achieved, and simplicity and cheapness are made possible in connection with precision instruments.

While I have shown a preferred embodiment of my invention, it should be understood that various changes and modifications may be resorted to, in keeping with the spirit of the invention as defined by the appended claims.

I claim:

1. As an article of manufacture a gauge member which consists of a body portion and a gauging surface formed on the body portion, said body portion formed of granite and said gauging surface presenting a multiplicity of tiny irregularitiesl resulting from grinding the granite at right angles to the head grain.

2. A gauge tool comprising a body of igneous rock which includes a multiplicity of very small particles arranged in a definite pattern to constitute a head grain extending continuously from one side of the Hoody to an opposite side along a denite axis, said tool presenting a gauging surface which is dened by a plane cutting perpendicularly across the said axis and intersecting two other sides of the body.

3. Means constituting a working surface for slidably engaging metal bodies, comprising a granite base material which includes a multiplicity of very small particles arranged in a deflnite pattern to constitute a head grain which extends continuously from one side of the granite base material to an opposite side thereof along a definite axis, said granite material presenting a Working surface which is defined by a plane cutting across the said axis substantially at right angles thereto.

JOHN B. HALL.

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