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Патент USA US2410877

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ì J. B.' HALL
Filed Aug. 27, 194s
2 sheets-sheet 2
día.. 6M
Patented Nov. 12, 1946
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)
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
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.
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
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
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
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
cases to eliminate resurfacing throughout
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
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 ,
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
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
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
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