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Manufactured by Herbert Hunt & Sons with works in Elsinore Road, Old Trafford, Manchester, the Hunt range of drill grinders were heavy, industrial machines and sold well for many decades. In addition to "Hunt" the machines have also been found carrying Churchill, Dormer, Herbert and Jones & Shipman badges. Although made in several sizes, all used the same, relatively simple operating procedure that allowed even unskilled workers (given just a minimum of training and a little practice) to produce good results.
Early machines were numbered simply as the Types 0, 1 and 1A Standard (these versions being intended for two-lipped drills only); the No. 2 and No. 3 Universal (able to grind two, three and four-lipped drills); No. 2 and 3 Automatic (identical in ability to the Standard models but with all motions, including an in-feed to the drill, driven by a separate 3-phase motor - these varying in power from 0.5 to 0.75 h.p.) and the No. 4 Standard. By the 1950s the range had been renamed as the DG Series with models types including the DG2S, DG2A, DG3S DG3A and later still (reflecting metrication), the DG50 (2" capacity) and DG100 (4" capacity) automatic types, this latter pair differing from the original versions in having the grinding wheel instead of the drill holder set to oscillate.
Often described as the "Hunt's Patent", the machine was carried on a heavy cast-iron base and consisted of a grinding wheel fitted to a belt-driven, ball-bearing-supported spindle with a compound slide assembly used to carry the drill holding table - the latter arranged to swing to and fro by hand on the Standard models and by motor drive on the Automatics. On the later DG50 and DG100 Models instead of the drill swinging it remained stationary, with the wheel head arranged to swivelling instead The reason for this change was several-fold: to increase the speed of metal removal without burning, to allow a wider range of point angles to be ground (from 80° to 180° - or beyond if used for trepanning points to drill thin sheet steel) and to obviate the difficulty of grinding very long drills when, as the drill-support table swung to and fro, there was a danger of the drill end catching a workman's clothes - or worse. With this new arrangement, the Hunt grinder could safely handle extraordinary long drills, up to 10 feet long or more. On all models the plain end of the drill was held in either a self-centring 3 or 4-jaw chuck (or a Morse taper for Morse-taper shank drills) with the end to be ground supported in a hardened bush - the latter not needing to be an exact fit as the drill only needed to be set so that it rested against the lower inside surface of the bush; a range of bushes was supplied in standard sizes with each machine. In operation the drill was revolved by hand through a system of gears and, by the swivel action of the drill-support arm, the same clearance was given to each cutting edge - this being adjustable to make the drill suitable for working through hard or soft materials. Bevelled corners were also generated, these being claimed to extend the drill's survice life before re-sharpening was required. Point thinning - the process by which the straight line formed where the flutes faces meet at the point of the drill - was cut away (thinned) at each side by a movement of the cross slide that brought the drill under a separate, narrow, thinning wheel carried on an extension to the shaft on which ran the main wheel. Drill bits used for heavy feeds often have much thicker webs than standard and are neither intended nor suitable for use without thinning; any drill with a web thickness greater than one-eighth of its diameter should be thinned. A demonstration of point thinning can be found here).
A machine designed for a long life, all the slides were adjustable, the swivel slide - its surfaces were equipped with hardened steel inserts - turned on rollers and grease cups and oilers fitted where necessary. An essential element in the successful grinding of drills was an adequate supply of coolant, this being lifted from a tank within the base by (on early models) an impeller pump driven by a friction disc fitted to the spindle drive pulley - the latter taking its drive from either a built-in motor or arranged so that it could pick up a belt from overhead line shafting..
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