Patent GB-627828-A (GB)
Title: Improvements relating to rock drilling apparatus
IPC: E21B19/081
Filed: 1945-05-22
Abstract: 627,828. Percussive drills. HOLMAN BROS., Ltd., and ORAM, M. May 22, 1945, No. 12739. [Class 124] [Also in Group xxn]  A rock-drilling apparatus comprises a stationary support 1 carrying a rotatable feed screw 3 driven by an air-operated motor 4, a drill head 2 longitudinally slidable in the support and having a nut engaging the feed screw, and a drill bit which can advance to a limited extent relative to the support without rotation of the feed screw, the feed motor being controlled in accordance with the extent to which a gap between two parts of the apparatus is closed by advance of the drill bit. In one form, the invention is described as applied to a percussive drill Fig. 1, in which the drill head 2 is slidably mounted on a support or cradle 1 adapted to be clamped to a column and rotary valve 5 operable by a handle 51 controls the supply of air to the drill-actuating motor through a passage 53, Fig. 1A, and to the feed motor 4 through a passage 54, a spring-loaded valve 6 and a hose 55; air pressure is supplied to both chambers of the valve 6 by passages 63, 64. A passage 65 leads from the upper chamber of the valve to a spring-loaded valve 71 which is mounted on the drill head and communicates with atmosphere. When the drill bit has penetrated a short distance, the gap between a shoulder 74 on the drill holders and the valve 71 is closed and the valve is opened, thus raising and opening the valve 6 to supply air to the feed motor to feed the head forward until the valve 71 is moved clear of the shoulder; an automatic step-by-step feed is thus provided. The automatic feed may be cut out by pressing in a spring-loaded valve 66 and exhausting the pressure in the lower chamber of the valve 6 through a passage 68 so that the valve 6 remains closed. The feed motor has a reversing valve 41 to permit retraction of the head, during which the valve 6 is open as its upper chamber is exhausted through the passage 65 and the valve 71; alternatively, the valve 5 can be set to a position in which air is supplied to the feed motor only and the passage 65 is exhausted through a slot (not shown) in the valve 5. On completion of retraction the head engages a rod 42 connected to the reversing valve and stops the feed motor. The feed motor may be provided with a metering valve 43 to effect manually-controlled feed if the valve 6 is omitted. In a modification, the support is aligned with the head and the feed motor has spikes to engage the floor of a mine working. The feed screw coacts with a nut within a tube which is fixed to the head and telescopes into a tube fixed to the feed motor. The feed cut-out valve is disposed in a control handle projecting from the drill head and the reversing valve is operated by foot plungers. Rotary drills.-In a modified form as applied to a rotary type drill, the feed screw 3 Fig. 3, is splined to the feed motor shaft and engages a nut 22 on the head. The feed screw is urged forward relatively to the support 1 by resilient means comprising a rubber bushing 82 bonded to an outer sleeve 81 having a lug acting on a collar 31 on the feed screw and to an inner sleeve on which is a worm wheel 84 rotatable by a worm 86 for adjustment of the resilient pressure. Also engaging the collar 31 is a lever 32 that operates a valve 6 controlling the supply of compressed air to the feed motor. With the feed screw held in the forward position and the valve 6 open, the head moves forward until the drill contacts the work when the head and feed screw will be moved back against the action of the rubber spring, closing the valve 6 and stopping the feed. The drill is held against the work by the rubber spring until the drill has penetrated sufficiently to allow the feed screw to move forward to close the gap between a collar 90 and the cradle, so opening the valve 6 and restoring the feed. Specification 522,734 is referred to.