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Hobrough Surface Grinder

A Manual is available for the Hobrough Grinder

Little-known and now seldom found, the Hobrough was one of the very few machine tools to have been manufactured in Wales. Of conventional layout and design, the Hobrough was, in effect, a developed copy of the well-known and proven American-built Brown & Sharp No. 2 Three models were available, mirroring those offered by Brown & Sharpe, all with 18 inches of longitudinal table travel and 6 inches in traverse: the Type 2AA had all-hand feeds to the table, the Type 2BA the addition of power longitudinal feed and the top-of-the-range Type 2EA with both power longitudinal and traverse feeds - the following description applying to the latter.
Table travel was electro-mechanical and mechanical in action - the mechanism employed to produce the automatic reversing left-to-right, right-to-left table travel being by a "feed box" that contained no gears and needed no lubrication. In place of gears, magnetic clutches operating at 90 volts DC were used, the whole assembly able to be replaced by a service exchange unit (that the factory kept in stock for immediate delivery) in less than 30 minutes. Drive was by a separate 1/4 h.p., 940 r.p.m. motor mounted in the rear of the cast-iron base, an "expanding and contracting" var-speed pulley on its shaft driving a large, front-mounted V-belt pulley. To open and close the pulley - and so change the output speed - a knurled knob was provided to move the motor platform backwards or forwards, this providing a rate infinitely between limits of 25 and 35 feet per minute. Unfortunately, to change the setting, the door on the front face of the stand had first to be openedů.
Set above the box - and driven in opposite directions by a continuous flat belt - two pulleys were fitted, each holding an electromagnetic clutch controlled by mercury switches tripped by the table dogs. With one clutch engaged - say for travel of the table left to right - drive then passed, via a belt driven by V-pulley on the clutch output shaft, to a further shaft above fitted with a pinion that engaged the table rack. When the table tripped the stop dog at the end of its travel, the other clutch was automatically engaged, the rotation of the output shaft reversed and the table moved in the opposite direction.
When operated by hand, one turn of the table's longitudinal handwheel produced a travel of approximately 2" - the wheel able to be disengaged against a spring-plunger for safety reasons when power drive was engaged.
More mechanical ingenuity was to be found in the table's automatic cross travel, the limits of its movement being controlled by stop dogs mounted in a T-slot on the saddle's right-hand face. A friction-type arrangement, the automatic cross-feed mechanism could be set to index the feed in, or out, at either or both ends of the table travel - the setting being achieved by two knurled-rim nuts set in partial-circle slots on the face of the unit. Feed rates (at each change of table direction) from 0.01" to 0.09" were available, a large knurled-edge nut in the middle of the assembly being used to engage and disengage the drive; with the mechanism in the latter state the cross-feed could be manually operated without fear of the drive re-engaging.
The spindle assembly - described by the makers as a "
Boneham & Turner Precision Replaceable Quill Type" and running at 2830 r.p.m. - was driven by a 1 h.p. motor and raised and lowered by a large-diameter handwheel connected to a pair of bevel gears - the horizontal one of which was threaded to take a non-rotating, precision-cut, heat-treated screw. Being of a considerable size, the handwheel rim was used as the micrometer dial, the widely-spaced graduations reading to 0.005"
Saddle ways (for the in-and-out feed) were of the V-type and the table ways of V and flat with roller lubrication..


On the left the Hobrough and, to the right, the grinder on which it was based: the Brown & Sharpe No. 2 as manufactured during the 1930s



A Manual is available for the Hobrough Grinder

lathes.co.uk
Hobrough Surface Grinder
email: tony@lathes.co.uk
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