IMPROVEMENTS IN TWIST DRILL GRINDING APPARATUS
Year: 1879

page_text: PROVISIONAL SPECIFICATION left by William Darling and Robert Varley
Sellers at the Office of the Commissioners of Patents on the 8th May
1879.
WILLIAM DARLING and ROBERT VARLEY SELLERS, of the Firm of Darling &
Sellers, Airedale Works, Keighley, in the County of York, Tool Makers and Iron
Founders. "IMPROVEMENTS IN TWIST DRILL GRINDING APPARATUS.”
Our Invention relates to apparatus for holding twist drills in position to give
them positive, equal, and true ground cutting edges. For this purpose we employ
a compound slide rest, which we fix to an ordinary grindstone or emery wheel.
On the top of the compound slide rest we fix a bracket having a boss, and this boss
may be cut through so as to press more or less on a spindle which passes through
the boss; or the side of the boss may be made with a projection, in which screws a
set screw to secure the spindle in position. The spindle is made with a small
reduced end, and by preference the reduced end is cut partly away on the side.
The spindle when passed through the split boss, and when placed to the required
holding position, is screwed in the boss by a set screw fitted in the boss. The spindle
can be set either in a vertical, horizontal, or angular position, and can be set to any
size drill to catch the groove or spiral of the drill; or the spindle can be set
to catch the groove or spiral on either side or on either edge of the groove or
spiral.
The twist drill to be ground is secured in a support which is by preference made
with a V groove, which allows several sized drills being secured therein. The
support is secured to the required angle on the top of the compound slide rest, and
to secure the drill in position in the groove we employ a spindle which receives a
lifting and lowering action by means of a screw, and on the end of the spindle is
fitted a loose foot of suitable form for holding the drill in position by pressing on
the top of the drill and adjusting itself to the angle at which the drill is set for
grinding; the spindle and screw work in a bearing secured to the side rest. A
stop is also employed, which prevents the drill moving longitudinally. The stop
works in a slot hole made in a bracket secured to the slide rest, and the stop is
secured in position by a thumb screw.
The drill having been fixed in position the reduced end of the spindle is brought
in contact with the groove or spiral of the twist drill at any suitable part of the
groove, or on either side, or on either edge of the groove or spiral. The drill is then

page_text: brought in contact with the grindstone or emery wheel, cutting the edge, and to
cut or grind the other edge the drill is released in the V groove of the support, and
the drill given a half turn; the reduced end of the spindle is brought in the other
groove or spiral, or in alternate groove or spiral, by which means the exact half
turn is obtained, and the edge of the drill being brought in contact with the grind-
stone or emery wheel gives a positive, true, and equal cutting edge to the edge
previously cut. The compound slide rest on which the apparatus is fixed can be
either drawn back from the grindstone or emery wheel, and set up to the same
place by having an index, or it can be moved off the side of the grindstone or emery
wheel until the required half turn is given to bring the next edge to be cut into the 1
proper position for grinding.