IMPROVEMENTS IN ROCK DRILLS
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by James William Larmuth and Robert
Birken Howarth at the Office of the Commissioners of Patents on the
16th February 1883.
JAMES WILLIAM LARMUTH and ROBERT BIRKEN HOWARTH both of Pendleton
in the County of Lancaster, Engineers "IMPROVEMENTS IN ROCK DRILLS
Our Invention relates to improvements in rock drills and is more particularly
applicable to that class of drill in which the boring tool is carried by a recipro-
cating and rotating piston actuated by fluid pressure. The objects of our invention
are to economise the consumption of the said fluid pressure and generally to
simplify and render more efficient the class of machine under consideration. Rock
drills as hitherto constructed are usually furnished with a valve which directs the
pressure through ports to the interior of the cylinder. In many instances these
ports are of considerable length and capacity and have to be filled with pressure at
each stroke of the drill. In accordance with our Invention we form on or attach
to the cylinder a valve chamber equal in length to the cylinder and containing a
valve consisting of a spindle having a slide valve at each end which works over
inlet and exhaust ports leading to the interior of the cylinder-the length of the
said ports being equal only to the thickness of metal of the side of the cylinder
where the valve is applied. By this arrangement the pressure has only to fill at
each stroke a short port of small capacity instead of a long passage of large
capacity as heretofore and consequently a great saving of the fluid pressure
employed is effected. Another improvement which we apply to the valve consists
of an arrangement for locking the valve in position when it has been moved one
way or the other so as to prevent the shock of the blow from disturbing the valve.
The central part of the valve spindle is enlarged and recessed to permit the
introduction of the tail of a three armed tumbler which is pivoted on a fulcrum
fixed to the cylinder. The curved shoulders of a recess turned in the piston act
alternately upon each of the two lower arms of the said tumbler and cause it to
rock upon its' fulcrum and by means of the third arm to reciprocate the valve.
In executing this movement which is effected without the shock which is so
destructive to the cams of ordinary rock drills the nose of one of the lower arms
slides up the curved shoulder on the piston and rests upon its circumference while

page_text: the other arm is depressed so as to act upon the bottom of the recess in the piston.
The tumbler is thus held immovable between these two points and prevents any
accidental shifting of the valve when the blow is delivered.
Our improvements relate further to the means for advancing or feeding the
boring tool when the machine is in action. Under the arrangement at present in
use when the feeding screw and nut have become so worn as to permit of a little
play the shocks of the boring tool cause great jarring of the screw and feeding
bandle and are the occasion of inconvenience and injury to the operator. To
obviate this disadvantage and to increase the usefulness and durability of the said
feeding screw and nut we apply a secondary binding nut to the screw in the rear
of the usual nut. The said binding nut is carried on screwed studs projecting
from the rear of the machine in line with the feed screw and by tightening nut on
the ends of the said studs the secondary binding nut is forced towards the feed
nut and the feeding screw is pinched between the nuts and prevented from
jarring or the distance between the nuts may be increased to obtain the same
result,