Improvements in Machinery for Grinding and Polishing Slates and other similar articles.
Year: 1891

page_text: Date of Application, 20th Oct., 1891-Accepted, 21st Nov., 1891
COMPLETE SPECIFICATION.
[Communicated from abroad by JUSTUS HENRY RUDOLPH, of Walnut Port,
Pennsylvania, United States of America, Manufacturer.]
Improvements in Machinery for Grinding and Polishing Slates and
other similar articles.
I, William Henry Beck, of 115 Cannon Street, London, E.C., Consulting
Engineer & Patent Agent, do hereby declare the nature of the said invention and
in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement
--
My invention relates to the polishing of the surfaces of school slates and the
While designed
reduction of the slate to a uniform thickness throughout its extent.
specially for this purpose the invention may be used for the reduction or polishing
of like surfaces where the material is difficult to handle and a uniform surface
desired upon one or both sides.
As the slate comes from the quarry it is of varying thickness and uneven surface;
it is brittle and easily broken by pressure applied to the surface and hence requires
great care in the handling, especially in view of the fact that the sheets are usually
very thin in order that the greatest possible yield may be obtained from the slate
quarry. These thin sheets of slate are usually slightly curved and this increases
the tendency to breakage and the necessity for great care in the manipulation of the
slate in the reduction and polishing of the same.
It is the object of my invention to provide a method of holding and applying this
slate to the abrading surface whereby all tendency to rupture is avoided and an
even and uniform surface produced without regard to the thickness of the slate or
the amount of curvature. A further object is to provide means for carrying out of
the main object of the invention.
The invention consists primarily in the art of grinding and polishing or reducing
the surface of slate or like material by first securing said slate to a holder forming
a rigid backing against which the slate is securely clamped and in applying the slate
so held face downward to the action of an abrading surface and allowing it to feed
automatically by gravity.
The invention further consists in the devices and combination of devices herein-
after fully described and particularly claimed.
In the accompanying drawings:
Figure 1, represents in side elevation a form of table with the abrading disc and
the means for driving it shown in dotted lines.
Figure 2, is a plan view of the table shown in Figure 1.
Figure 3, is a detail view of the slate holder with a slate in place and
Figure 4 is a modified view of the clamp for the slate.
Figures 5 and 6 show the holder with modified means of pivoting the said holder
so as to allow uniform movement throughout its extent as the slate is reduced.
Figure 7, shows a means of adjusting and regulating the movement of the holder
and the slate carried thereby.
Figure 8 represents a holder for the slate adopted to permit the sides or ends of
the slate to be bevelled off.
In carrying out my invention I take the sheets of slate and first bevel the edges
by presenting the slate to the action of an abrading disc while held at an angle
thereto as shown in Figure 8 in which a post a supports an angular holder pivoted
thereto, the slate passing through an opening in the base 6 while its upper ends fits
beneath a flange c. An abrading disc operated in any suitable manner as by the
belt and pulley v, w, is directly beneath the base b; and hence the end of the slate

page_text: projecting through the base comes in contact with the abrading surface at an
angle so that the edge of the slate is bevelled. The action of the abrading surface
continues until the straight sides of the post a and the corresponding part of the
holder e meets, thus forming a stop and preventing further downward movement of
the angular holder. To vary the amount of bevel a stop screw is provided to
check the pivotal movement of the angular holder at any point. Instead however
of the means described for bevelling the edges of the slate this may be effected by
other means, though I prefer the means described.
After the edges of the slate have been bevelled I place the slate upon the face of
the slate holder A. which is preferably of metal and sufficiently strong for the
purpose.
On its face at one end it is provided with a raised ledge having its front edge
forming one wall of an angular recess corresponding to the bevel of the slate edge
which is adapted thereto.
At the opposite end of the holder is a clamp g which after the slate is placed
upon the surface of the holder is turned up until its projecting lip h, engages the
bevelled edge of the slate. The clamp may be prevented from displacement by a
spring bearing against a projecting lug such as shown in Figure 4 or other means
may be used for this purpose.
The surface of the slate thus held by its bevelled edges projects beyond the faces
of the ledge and the clamp g, and as it is held against a perfectly plane bearing
there is no tendency to rupture and any curvature in the slate is without effect in the
operation of reducing the surface to interfere with the uniformity of the surface, as
this curvature disappears in the clamping of the slate against the plane surface.
The holder with the slate carried thereby is then inverted and applied to the surface
of an abrading disc uutil the lower surface of the slate becomes smooth and
uniform, after which the slate may be removed and reversed in position and the
opposite side reduced in like manner.
In order to hold the slate in the two positions the ends of the slate are bevelled
outwardly from one surface while the sides are bevelled outwardly from the opposite
surface.
While the holder may be applied to the abrading surface by the hand of the
operator I prefer to support the holder above an abrading surface and to auto-
matically regulate the downward movement of the holder so as to insure an even
surface on the side first polished and a definite reduction of the slate on the opposite
side in order that the slate may not be ground down too thin. To this end I show
in Figures 1 and 2 a table C which has a series of openings in its surface and
beneath the level of this table in line with the opening, an abrading surface D is
revolved.
The enlarged views of Figures 5 and 6 show the holder working in the openings
and having projecting ledges i, i, of greater extent than the opening. In Figure 5
the holder is secured to the edge of the table by means of a link k which allows the
holder to move uniformly so as not to cause any irregularity or inclination in the
surface of the finished slate. In Figure 6 the pivot of the holder is held between
two upright lugs while in Figure 7 the holder A is guided in its movement by
posts m and regulated as to its movement by nuts n engaging screw threads on the
posts. It will thus be seen that by providing for the regular downward movement
of the holder and a.stop to limit its movement, which may be a table as shown in
Figures 5 and 6, or the nuts as in Figure 7 or equivalent means, the slate held by
the holder may be reduced to an absolutely even surface and to a uniform thickness,
this thickness being predetermined by the amount of movement allowed the holder,
as it will be readily seen that the abrading surface will continue to act to reduce
the surface of the slate until the downward movement of the holder is checked and
the abrading action then ceases.
By employing the table C with openings and allowing the slate to
matically downward, the grit and water which it is necessary to use is
the grinding disc and the workman is protected from flying sund or grit.
feed auto-
retained on
It may be

page_text: pointed out also as an advantage arising from the arrangement of the disc with the
grinding face upward that as the grit and water floats on its upper face the grit
removed from the slate is caught and retained to aid in the grinding action.
It will be observed that by inverting the holder and presenting it to a grinding
surface below it that the feed is entirely automatic and the attendant need only
adjust the holder in position and properly place the stops and then the device
requires no further attention until it is filled again. In this way one attendant can
keep in operation number of holders and even should one holder be neglected it
would have no disastrous effect as the downward feed of the plate would be arrested
by the stops at the proper time.
I claim as my invention:
1. In combination, a grinding disc arranged with its grinding face upward, a
holder for the slate arranged with its face downward and movably supported above
the grinding disc to fall automatically by gravity, and a stop for limiting the down-
ward movement of the holder substantially as described.
2. In combination, a grinding disc arranged with its grinding face upward, a
holder for the slate arranged with its face downward and a top or covering plate
above the grinding disc having an opening through which the slate holder moves
toward the grinding disc.
3. The improvement in the art of grinding or polishing and straightening slate or
like thin material, consisting in reducing the side edges towards one face and
reducing the end edges reversely to receive an overhanging clamp, then clamping
the slate by its side edges to a backing plate to straighten the same, presenting it
thus held to a grinding disc, then reversing it and clamping it by its end edges to
complete the straightening and subjecting it as thus held to the action of the
grinding disc.
4. In combination, the grinding disc, a slate holder having movement towards
the same, a stop for limiting said movement, the said holder being pivotally
supported substantially as described.
Dated this 15th day of October 1891.
W. H. BECK,
115, Cannon Street, London, E.C.