IMPROVEMENTS IN MACHINERY FOR DRESSING OR CUTTING MILLSTONES
Year: 1868

page_text: PROVISIONAL SPECIFICATION left by Augustus Bryant Childs at the
Office of the Commissioners of Patents, with his Petition, on the
22nd August 1868.
I, AUGUSTUS BRYANT CHILDS, of No. 16, Mark Lane, in the City of
London, Engincer, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN MACHINERY FOR DRESSING OR CUTTING MILLSTONES," to
bé as follows:-
My Invention relates to dressing or cutting the grinding surface of
millstones with diamonds or other hard mineral substances in a more
expeditious and perfect manner than has hitherto been practicable.
The said Invention consists chiefly in giving to the diamond tool or
cutting point a peculiar compound motion, and also in the devices for
producing such motion in combination with the devices for holding the
diamond and for moving the same in the required direction over the face
of the stone. I prefer to dress the stones with a spiral "crack" or
groove extending continuously from the centre to the periphery of the
stone. To produce this spiral "dress" it is necessary that the diamond
tool or point should move to or from as well as around the centre of

page_text: the stone, I therefore attach the tool holder to a travelling frame or
carriage, which is fitted to slide endwise upon a radial horizontal arm
or bar extending from a vertical shaft which rotates at the centre of the
stone. This sliding carriage is caused by suitable gearing to travel
endwise on the radial arm as the latter turns with the central shaft, the
motions of the shaft and carriage being so proportioned to each other
as to give the required "pitch" to the spiral "dress." The diamond
holder is fixed upon a horizontal spindle or axis, and in order to
accelerate the cutting of the spiral "dress," and also to prevent the
fracturing or blunting of the diamond point, I give to the latter, besides
the motions above described, a rapid rotary motion around the said
spindle or axis, such rotary motion being derived from the motion of
the horizontal arm and imparted to the said spindle by means of belts
and pulleys or other suitable gearing. If desired two or more diamond
tools, each carried on a separate arm, may be employed. The horizontal
arm is securely keyed upon a vertical spindle or shaft which rests in a step
fixed over the eye of the stone to be dressed, and revolves freely in a
socket or bearing carried by a frame which extends across the top of the
stone; this arm is accurately planed on the greater portion of its length,
and the apparatus which carries the framing for holding the diamond
and the gearing for working the same travels on the said portion. The
spindle of the diamond holder is made to revolve rapidly by means of
a stationary bevel or face wheel fixed to the under side of the central
socket or bearing on the frame. This wheel gears into a small pinion
fixed on a shaft which is carried in bearings attached to the horizontal
arm. This latter shaft is by wheels and pulleys and an intermediate
shaft or spindle connected to the spindle of the diamond holder. The
movement of the apparatus which carries the diamond tool along the
horizontal arm is effected as follows:-Upon the under side of the
stationary bevel or face wheel above mentioned is cast or otherwise
securely fixed a worm or screw, into which is geared a worm wheel
which is carried on a spindle extending endwise along the horizontal
arm; the outer extremity of this spindle carries a small spur wheel
which gears into another spur wheel fixed on a screw which extends
from end to end of the arm and which is fitted to work through a nut
attached to the tool carriage. When the vertical spindle with its
horizontal arm revolves, the worm wheel which is geared with the fixed
worm and whose spindle turns with the said shaft and arm is caused
to rotate on its axis at a speed depending upon the relative proportion

page_text: of the number of teeth in the worm wheel and worm. The motion of
the worm wheel is through the spindle and spur wheels imparted to the
feed screw, which may be arranged to propel the tool carriage either
towards or from the centre of the stone; the pitch or distance between
each turn of the spiral groove in the stone may be regulated by varying
the proportion of the worm wheel and worm, or by varying the relative
size of the spur wheels or the pitch of the feed screw, so that if desirable
the pitch of the spiral groove may be so arranged as to dress the stone
to a perfect face or floor. At a convenient part of the frame which
carries the diamond spindle I arrange a pointer, which can be removed
at pleasure for the purpose of adjusting the face of the stone in relation
to the framework of the machine before commencing the operation of
dressing. When two or more horizontal arms and tools are employed
the mechanism of all of them may be operated from the same worm and
bevelled wheel.
The diamond holder is constructed with two circular plates or discs
of steel or other suitable material, which are accurately bored to fit the
spindle to which they are attached; the inner faces of these discs are
formed with dovetail recesses, which are made of a convenient depth
and filled with a soft metal, by preference that known as "Babbitts"
metal. Small recesses are made at the periphery of these discs-corre-
sponding with each other, in one of which the diamond is inserted in
such a manner that when the two discs are screwed up face to face with
each other the diamond is firmly embedded therein, the soft metal
yielding to a certain extent to the pressure; the diamond thus finds its
own bed, the pressure required to hold it being equalized upon all points
of its surface. The diamond is by this means securely held, while at
the same time the danger of breaking it by unequal straining or
compression is entirely obviated.