ì2, w46. ' - , , ` ì J. B.' HALL 2’4i0’8î7'7 DIMENSION GAUGE- Filed Aug. 27, 194s i 2 sheets-sheet 2 Iaweazêoa’l: día.. 6M Patented Nov. 12, 1946 2,410,877 » UNITED STATES PATENT OFFICE 2,410,877 DIMENSION GAUGE JohnB. Hall, Wakefield, Mass.,v assignor of one half to Frank I. Hardy, Boston, Mass. Application August 27, 1943, Serial No., 500,269 3 Claims. (Cl. 33-174) l 2 This invention relates to improvements in tools whenexposed to temperature changes and other and more especially to improvements in gauges conditions, and that these substances lend them» of the type employed in making precision selvesto formation into various types of precisionmeasurements whereby mechanical parts are tools, inV which form the rocks provide various brought into close conformance with accepted 5 advantages in comparison with metal. Examples standards; of materials suitable for this purpose are the Examples of precision tools of the character rem igneous» rocks, such- as granite, gabbro, diorite, ferred‘ to are surface plates, snap gauges,> plug díabase, basalt, trap, rhyolite, and others. gauges, angle irons, pedestals, and many others. The‘term “igneous rock” as employed in geology Thesetools are customarily made of metal, a ma, i‘ef'ersto a class-'of substances which were formed terial which is subject to the development of. ln by heat beneath the earth’s crust and forced to thel surface by pressure, thereafter forming an accuracies` from Various causes. For instance, metal develops dimensional instability upon ex extremely hardì mass through a period of slow posure 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 appliedthereon, and also internally of the metal from stresses and strains within the metal itself. Gauges of metal are further subject to Wear which 20 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 sub likewise causes inaccuracies. In the case of some stantially unaffected by temperature changes, and is highly incompressible. Igneous rock is dis tinguished fromK “sedimentary rock” by the fact of these tools, as for instance surface plates,` it is that the latter substance is formed by deposits necessary t0 provide relatively large surfaces nn in thelabsence of heat. ished to- a line tolerance. ‘ Such surfaces cannot There occur in nature several'types of granite be accurately formed by conventional grinding 25 which are, further classiñed as biotites, hornblend, operationsand as a result, hand’ scraping opera tions are necessary which require considerable biotite-muscovite, and> quartz-monzonite, andthe like. Of‘these; the largest number of so-Called commercial granites. utilized in connection wit 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 the invention,_ are biotites. ' Referring more in, detail to the application of devise means for overcoming er substantially re igneous rock to precision tools, I have disclosed ducing the various difliculties above noted. It isv a further object of the invention to. provide irn proved gauges which are characterized by cheap. ness, durability, and more eíîcient operation. The nature of the invention and its objeetswill. be more fully understood from the following. de in Fig. l' a preferred embodiment of the inven tion, consisting of a surface plate I which is com posed entirely of a granite such as biotite. The surface plateco-nsists of a flat slab of the granite. scription of the drawings, and discussion relating. thereto. In the accompanying drawings: 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 v a grain formation made up of tiny peaks 5 and. Fig. l is a perspective view illustrating a sur pits or depressions 6. ¿characteristic of the granites is a well-deñned grainV formation which may be visualized as re face 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 sur sulting from face plate illustrating a ground surface; 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 Fig. 4 is a perspective View illustrating a modi-V fication of the invention; Fig. 5 is a perspective view illustrating‘still an other modiñcation ofthe invention; and Fig. 6 is a View in. cross section further illus trating the modiñcation shown in Fig. 5. The invention generally includes the discovery that there is a class of natural rocks which are substantially free from dimensional instability multiplicity of tiny flat particles 45 piled one> upon another in a definite pattern of 50 its particles includes the characteristic heads 5î 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 pro 2,410,877 ` 3 slidability. 4 various sizes, which may be used in a wide range vide an extremely accurate supporting surface for assembling work which must be finished to close tolerance (.0001-.0005). Such a require ment calls for an exceedingly smoothly finished surface which, in the case of metal, may reduce 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 In the case of a surface plate espe cially, 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 ñne tolerance, conditions. Such deflection is generally recog nized as being due to a slight resiliency present in metals, especially those which may include stresses and strains. 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 The matter of deñection 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 tend ency to flex under any pressure conditions, due to its highly incompressible mass formed under 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 heat and pressure and subsequent slow cooling "freezing” is automatically avoided. In place of the hand scraping operation com 20 by natural processes. The tendency of metal surface plates to Wear, monly carried out on metal, the present plate results in the need for frequent correction and is surfaced by a grinding operation, utilizing resurfacing operations of expensive character. granite surfaces which are applied to the surface This problem of Wear is greatly minimized by tc be ground, in conjunction with the use of a While the 25 the use of granite as the latter material suc cessfully withstands usage with a highly de veloped resistance to wear which has not been fully determined but which is understood to in the manner described, it may nevertheless be greatly reduce resurfacing operations, and in desired, for some types of tools, to utilize the some cases to eliminate resurfacing throughout 30 granite with the grain running in other directions the life of the tool. than at right angles to the plane of the surface fine abrasive such as carborundum. surface 4 is preferably formed from cleaving the granite across the grain to expose the head grain The surface plate of the invention is char acterized by various other advantages such as be Formation of a metal surface by hand scraping ing rust and corrosion resistant, and hence does operations is a diñicult and time-consuming op eration, made necessary by reason of the fact 35 not require applications of oil or grease to protect the finished surface. The surface itself can be that metal grinding equipment cannot be used reñnished in less time and at less cost than is the on account of deflection or distortion developing case with metal. The finished granite surface in the grinding members. In the case of the when damaged will not raise burred edges, which granite plate, however, surface grinding opera tions may be successfully carried out by the use 40 might scratch or mar lapped metal surfaces ap plied thereon. Instead of raising burred edges, of granite grinding members which are not sub the surface plate merely chips away, leaving only ject to deflection or other dimensional instability. of the plate. a depression. 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. 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 modifi One immediate result obtained from this ability of granite to serve as a grinding member as Well cation as a “table” gauge. as to be formed by grinding, is that close toler plates, whereas it is practically impossible to con form 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 com monly specified for a 12” square metal plate, while a 24" square plate can only be~ ground 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 60 plates. In use, the granite surface plate exhibits several unusual properties. It is substantially free from dimensional changes in the presence of fluctuat ing temperatures, and it is believed that if any change whatever does take place from changing temperature conditions, it does so in a very uni form manner, with the result that no irregulari ties 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 This gauge includes a base 'l consisting of a granite surface plate ances can be carried out on relatively large sized 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 ñne tolerance. In addition, the frame has a top anvil portion Il, with still a third gauging sur face 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 fur ther 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 75 with the upright 8, and affords a means of carry 2,410,877 , 5 ing out various gauging operations, all of which achieved, and simplicity and cheapness are made may be free from dimensional instability irre possible in connection with precision instruments. spective of temperature changes and other con While I have shown a preferred embodiment ditions. of my invention, it should be understood that Preferably the entire body of the upright frame various changes and modifications may be re 3 is formed of granite in order to resist any in sorted to, in keeping with the spirit of the in accuracies from temperature fluctuations. It vention as defined by the appended claims. may, however, be desired to form a part only of I claim: the upright of granite, with some other material 1. As an article of manufacture a gauge mem utilized for the remainder of the tool. Various 10 ber which consists of a body portion and a gaug other arrangements may be resorted to which ing surface formed on the body portion, said utilize the property of the granite of being free body portion formed of granite and said gauging from dimensional instability. surface presenting a multiplicity of tiny irregu A further modiñcation of the invention has laritiesl resulting from grinding the granite at ' been illustrated in Figs. 5 and 6, which disclose 15 right angles to the head grain. a straight edge member l5 also formed of an 2. A gauge tool comprising a body of igneous igneous rock such as granite, and including a rock which includes a multiplicity of very small straight edge surface I6, a rib portion I 1, and particles arranged in a definite pattern to con pedestals I8, with the rib portion I1 further being stitute a head grain extending continuously from formed with openings I9. This tool conforms in 20 one side of the Hoody to an opposite side along a all respects to the shape and style of a metal deñnite axis, said tool presenting a gauging sur straight edge but is characterized by the proper face which is deñned by a plane cutting perpen ties inherent in igneous rock as already set forth dicularly across the said axis and intersecting two in connection with previous modiñcations. Vari other sides of the body. ous other applications of igneous rock may also 3. Means constituting a working surface for slidably engaging metal bodies, comprising a Ábe resorted to in accordance With the invention, a-s for example in making ring gauges, plug granite base material which includes a multi gauges, buttons and anvils for snap gauges, and plicity of very small particles arranged in a defl others. Any of the Various igneous rocks as a1 nite pattern to constitute a head grain which ready referred to may be employed in this con 30 extends continuously from one side of the granite nection. » Ábase material to an opposite side thereof along a From the foregoing, it will be seen that I have definite axis, said granite material presenting a eiîected substantial improvements in gauges by Working surface which is defined by a plane cut means of which closer tolerance may be obtained, ting across the said axis substantially at right better resistance to wear is possible, freedom 35 angles thereto. from substantially all dimensional instability is JOHN B. HALL.