Manufactured from the late 1930s until the late 1950s, the Jones & Shipman 520 Miniature Cylindrical and Internal Grinder was intended for the manufacture of small parts such as internal dies, circular tools, punches, fuel injection components and parts for mechanical instruments, etc. Like the similar German-made Beling & Lübke No. 1, it was to be found in high-class tool rooms and such places as the Rolls Royce Experimental Instrument Department where the then leader, Mr. Gordon Hudson, devised a much neater yet more versatile drive system to replace the beautifully-made and effective but rather cumbersome "overhead".
A machine of very high precision - Jones & Shipman claimed an accuracy of 0.0001" and with a surface finish achievable of better than 1 micro inch R.M.S - the 520 could be supplied for bench mounting, or complete on the maker's superb 44" x 28" by 36" high oak cabinet with storage drawers and a built-on countershaft drive unit. The drive unit reflected contemporary practice and hence was a rather large and expensive construction: all shafts ran in ball races, everything that rotated was dynamically balanced to ensure that no vibrations reached the grinding machine and the system, powered by a 1425 r.p.m. 1 h.p. motor, gave the wheelhead and workhead three independent speeds each. Initial drive to the overhead was by V-belts with two smooth-running flat belts (in flax) used to drive the heads - each belt tensioned by its own jockey pulley. A multi-plate clutch and brake, operated by a lever, allowed the workhead to be instantly started and stopped independently of the wheelhead.
Even though small, the machine was massively built and weighed, net (including the bench and countershaft) over 750 lbs (340 kg). In addition, to ensure vibration-free running, all rotating parts (including the complete countershaft unit) were dynamically balanced
Able to accept a maximum of 5.25" (133 mm) between centres, the swing was 27/8" (73 mm) and the 7° swivel table, fitted with power feed, was 13.25" long and 2.75" wide (336 x 70 mm). Table travel was 7" (178 mm) with 1" (25 mm) in traverse and an adjustment of the wheelhead's position on the cross slide of 2" (51 mm). Drive from the handwheel was by step-down gearing to the cross-feed screw, one turn of the handle (graduated with markings showing 0.0001" of travel) advanced the slide by 0.01". To eliminate backlash, the cross nut was pulled backward by a weight suspended beneath the machine. One machine has been seem with a cross-feed dial incorporating a vernier scale - though if this was an original factory fitting, or a subsequent improvement to the specification, is uncertain.
Fitted as standard for external work to the wheelhead was a 5" x 3/8" (127 x 9.5 mm) grinding wheel with a 1" (25 mm) bore that, driven by a 1 h.p. 3-phase motor, ran at 3900 r.p.m. With a full 5-inch diameter grinding wheel the speed recommended was 3900 r.p.m.; with a 4-inch 5000 r.p.m. and with a 3-inch 6750 r.p.m.
The maker's brochure describes lubrication of the wheelhead's superfinished, nitralloy spindle as being by "filtered oil from a reservoir in the head" - but several machines have been found with a pair of either drip-feed or wick-feed oilers screwed into the bearing housings. Whether these oilers were an original fitting, or a subsequent modification by the works, is not known. In addition, the bearings are described as being of white metal - though machines have been discovered with ones in harder-wearing bronze - again, a possible modification in the light of experience. The whole spindle assembly was beautifully constructed with the white-metal version being described as having a spring-loaded segment to eliminate spindle flutter - the latter being identified as a cause of poor finishes and inaccuracy. End thrust was absorbed by spring-loaded, self-adjusting thrust washers, these absorbing the expansion of the spindle as heat built up during high-speed work, the system ensuring that grinding up shoulders was of consistent accuracy (if the grinding was towards a shoulder in the direction of the tailstock, once the spindle had been left to reach working temperature, the springs could be locked and so the setting preserved).
Two workheads were available - the workhead, as the name suggests, is that carrying the job to be ground and always driven in the opposite direct to the grinding wheel. To obtain as great a number of speeds as possible the wheelhead speeds, engaged by a friction clutch, were driven independently of the grinding wheel. For ordinary external work the Dead Centre workhead was used, this being for work mounted between centres or carried on a mandrel. The non-rotating, hardened and ground spindle was bored with a No. 1 Morse taper and carried on its end a bronzed-bushed flat-belt pulley with a drive pin to rotate the job - a set of balanced drive dogs (also called carries) being supplied. Three speeds were available: 375, 686 and 1250 r.p.m. The other workhead was a live spindle collet type for internal grinding, the job being held in a collet or 3-jaw chuck and the whole assembly arranged to swivel to allow the forming of tapered bores. The assembly was similar in construction that employed on a "precision bench lathe" with a hollow, superfinished, nitralloy spindle running in bronze bearings and fitted with a No. 5 Brown & Sharpe taper nose. Collets were retained by a threaded drawbar and handwheel - the 3-jaw chuck (at extra cost) being carried on its own No. 5 Brown & Sharpe arbor.
When delivered the machine was ready for work, fully wired with electrical switchgear and complete with small items such a balancing mandrel, centre points for workhead and tailstock, a set of grinder carriers to accommodate work up to 1" diameter and a full coolant system with all its electrical connections and a switch wired in--though on later models the coolant unit was to be charged extra.
A number of useful accessories were offered including a wheelhead for internal grinding and two internal spindles - one able to run up to 60,000 r.p.m. with a wheel capacity of 1/8" to 3/8" diameter and the other limited to 40,00 r.p.m with a capacity of 3/8" to 3/4". Two and three-point steadies were listed; angular and radius wheel-forming attachments; collets; adaptor sleeves; a Lo-Vo-Lite unit and a mounted diamond for wheel dressing.
Towards the bottom of this page is an example of a 520 installed in a home-based business in Sheffield that concentrates on the rebuilding vintage Scott Motorcycle engines. These, in case you don't know, are wonderfully individualistic machines of handsome appearance powered by a deflector piston, twin-cylinder, water-cooled, two-stroke engine of unusual design (and enormous frustration).
Interestingly a similar miniature grinder was built in Germany by Reiniger, Gebbert & Schall, though of simpler design but just as well constructed and finished..