An Improved Method of and] Apparatus] for "Gritting" Marble.
Year: 1885

page_text: An Improved Method of and] Apparatus] for "Gritting" Marble.
"
I, EDWARD JOSEPH DOUGLAS, of N° 100 Collins Street East, in the city of
Melbourne and colony of Victoria, Brassfounder, do hereby declare the nature of
my invention for "AN IMPROVED METHOD OF AND APPARATUS FOR GRITTING
MARBLE "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 "gritting" of marble, "gritting" being that part of
the marble polisher's work which immediately precedes and prepares the face of the
marble for "polishing." Hitherto "gritting" has been a wet process, the face of
the marble being wetted and rubbed by a grit-stone held in the hand of the
operator. Sometimes grit-stones of various degrees of fineness are used in
succession but they are always used wet. Now, according to my invention the
gritting" is a dry process and is performed by revolving emery-faced wheels of
peculiar construction. Generally two such wheels are used, one having an emery
face of finer quality than the other, and there may be more than two if so
preferred. By an "emery-faced" wheel I mean a wheel having an emery face on
its periphery. The peculiarity in the construction of such wheels is that they must
not be made of any rigid material, because if they are so made they will break and
gouge the marble slabs presented to them for treatment. They are therefore made
of some non-rigid material, and I have found the following to answer well. I take
a number of pieces of canvas say eighty-and cut them into a circular shape as
near as possible to the diameter of the wheel required-and I have found an eight
inch one to answer well. These I glue together with a composition consisting of one
part of treacle to ten parts of glue and I lay the pieces together so as to cross the
grain of its neighbour in order to prevent their subsequently unravelling. This I
then allow to dry and afterwards, when it is hard-bore a hole through the centre
and insert a metal (say brass) bush upon which the wheel is turned true. I then
soak it in warm water to wash out the adhesive composition of glue and treacle and
allow it to dry again. Finally, when thoroughly dry I first cover its periphery with
an adhesive coating-say of glue and then with an outer coating of emery
powder. For the first wheel I may advantageously use what is known as
N° 40 Emery and for the last N° 120 Emery.
These wheels are placed on a shaft revolving at say two thousand a minute and
the meshle elabo hold on to them by hand or by any suitable elastic pressure.

page_text: In a very short time-less than one quarter of that required by the old wet hand
process the marble will be perfectly "gritted." Before presenting it for polishing,
however, I prefer-although it is not absolutely necessary to put the finishing
touch by subjecting them to the action of a revolving wheel or roller made of
separate layers of bleached linen on the periphery of which is a coating of what is
commonly sold as a metal polishing composition, and consisting of a combination
of mutton tallow, flour of emery, and beeswax.
For gritting the grooves in marble faces I prefer to substitute a piece of walrus
hide of the requisite thickness for the pieces of canvas herein referred to as being
used in the manufacture of the non-rigid "gritting" wheels. I coat this walrus
hide with glue and emery powder as before.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is
First My improved method of “ gritting' " marble substantially as herein
described and explained, the essence of which consists in performing this operation
dry by means of one or more non-rigid emery-faced revolving wheels.
Second. My improved apparatus for "gritting" marble substantially as herein
described and explained, and which consists of revolving non-rigid emery-faced
wheels prepared preferably in the manner herein described.
Dated this twenty-third day of July One thousand eight hundred and