Patent GB-122735-A (GB)
Title: Improvements in Twist Drill Point Grinding Machines.
Inventor: HUNT HERBERT
IPC: B24B3/24
Filed: 1918-03-11
Abstract: 122,735. Hunt, H., Hunt, H. W., and Hunt, P., (trading as Hunt & Son, H.). March 11, 1919. Twist drills, sharpening; disk apparatus; driving and feed devices; work-holders. - Relates to machines for grinding the points of twist drills of the kind in which the twist drill is clamped in a rotary holder that is given an axial and a swinging movement, and consists in supporting the drill near the point in interchangeable bushes or sieeves that are formed with shoulders to facilitate the initial setting of the drills. The axial movement of the drill is effected by a cam, which rotates at twice the speed of the drill-holder. The drill is ground against the periphery of a grinding-wheel which is reciprocated parallel to its own axis. The machine is shown in elevation in Fig. 1 and in plan in Fig. 3. The grinding-wheel 34 is carried on a shaft 35 mounted in a bearing 36 capable of sliding axially on a frame projecting upwardly from the tray 3, which is fixed to a pedestal 1. On a block 4 also integral with the tray 3 slides a feed-table 5, which can be moved towards and away from the grinding-wheel 34 by a feed-screw 48. A plate 6 with a scoop-shaped end 6<a> is secured to a pivot-pin 7, the lower end of which turns in a socket in the feed-table 5. The plate 6 has radial guides, in which slides a block 8 carrying the drill-holding tube 11 and chuck 12. The swinging movement of the plate 6 about the pivot 7 is steadied by the engagement nf rollers on pins depending from the plate with an are-slot 9 in the feed-table 5. The drill-holder 11 is rotated by bevel gear 15, 17 from a vertical shaft 14 itself driven by bevel gear 18, 23 from a horizontal shaft 22 operated by fast and loose pulleys 29, 30. The vertical shaft 14 is mounted in a boss 13 projecting downwardly from the block 8, and rotates at twice the speed of the drill-holder 11. A cam 16 secured to the shaft 14 engages a steel stud on a cross-bar 6<c> on the plate 6 so that, for each half rotation of the drillholder, it is moved towards and away from the grinding-wheel 34. Springs 20 effect. the return movement of the block 8. A pin secured eccentrically to the lower bevel wheel 18 is connected by a link 25 to an arm 26 on the feed-table 5. The rotation of the bevel gear thus causes the plate 6 to swing to and fro about the pivot 7, one complete oscillation taking place during each half revolution of the drill-holder 11. To permit the necessary freedom of movement, the bracket 28 carrying the fast and loose pulleys is pivoted to a rigid bracket 27 and the shaft 22 is slidably mounted within the pulleys. The drill is held in the chuck 11 and is supported near its point by passing it through a bush 7b held in jaws 7a on the oscillating pivot 7. A set of such bushes to suit drills of various diameter is provided. The feedscrew 48 may be operated by a hand-wheel 53; or it may be rotated automatically by a projection 6<d> on the oscillating plate 6 striking a pivoted arm 54, to which is hinged a pawl 55 engaging a ratchet wheel on the screw shaft. A pin 53<a> on the hand-wheel 53 may disengage the pawl 55 after a predetermined rotation of the screw. In order to secure uniformity of wear on the grinding-wheel 34, its shaft and bearings are given an axial reciprocating movement by means of a centrally-pivoted lever 39 operated by a link 42 attached to the oscillating plate 6. The pine 44, 40 for attaching the link 42 to the plate 6 and the lever 39 to the tray 3 are arranged to engage any one of a series of holes. The link 42 may be lifted off the pin 44 by a handle 45, and the grinding-wheel 34 may then be moved out of the way to enable a drill to be removed from or inserted in the holder. When inserting a drill, the holder 11 is turned until a notch on a rigid sleeve 58 is opposite a pivoted index finger 57 and the drill is then secured in such position that one edge of a flute in the drill lies flush with a shoulder 7<d> formed on the bush 7<b>. The shoulders 7<d> lie about one-sixteenth of the intenior diameter of the bush above the axis. A single pulley and clutch may be used instead of the fast and loose pulleys 29, 30. The lubricant and waste material are guided by the scoops 6<a> to an opening 3<a> in the tray 3, through which they fall into a pan 47.