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Coronet Miniature Precision Lathes
Diamond, Jewel, Ruby  & Tiara
Diamond lathe Page 2   Jewel Lathe   Ruby Lathe

Coronet Wood-lathes Home      Miniature Precision Lathes
Coronet Instruction Literature is available, please email for details




Although to become famous for their high-quality wood-turning lathes and associated equipment, the Coronet Company began life as a maker of machine tools in a rather different field. At the Model Engineering Exhibition of 1946 they displayed not wood-working equipment but four new small precision lathes, three of which were plain-turning types and one backgeared and screwcutting. The plain lathes were the "Diamond" (with a flat-topped bed) and a pair with round, solid steel bar beds; the "Jewel", "Ruby". The screwcutting lathe was the 3" x 12" "Tiara" of which, unfortunately, no surviving example have been found nor any supporting paperwork.
Of rather conventional appearance, with a flat-topped, cantilever-form bed, the 2.25" x 6" "Diamond" had a headstock assembly that could be unbolted from the bed and a base that allowed it to be swivelled 10 in either direction from central. The spindle (plain-bearing and ball-race) was, apart from a 11/16" x 20 t.p.i. nose thread and a No. 1 Morse taper, identical to that used on the other lathes and could be exchanged for the high-speed version. A hand-operated feed was provided for the carriage, the overhung leadscrew (complete with a zeroing micrometer dial) passing, rather unusually, down the rear of the bed. Unfortunately, only a single swivel slide was provided (though with a very large and easy-to-read micrometer dial) carried on a post that fitted into a hole formed in the front of the saddle - the design allowing it to be adjusted vertically over a small range. While this arrangement provided a quick and easy way of adjusting the tool height (just like the fitting on a Round Bed Drummond) it did nothing for rigidity, the cutting tool being cantilevered well away from its mounting. Of the ordinary screw-feed type, the tailstock could be set over for the turning of slight tapers and was fitted with a proper compression-type barrel lock. It appears that the Diamond might have been intended for production in some numbers, the micrometer dials on tool-slide and leadscrew being pressure die-cast in Zamak, just like the ones fitted to the contemporary Myford ML7.
Described by the makers as
The Watch and Clockmakers Lathe and Multi Propose Machine, the tiny, 1.5" centre height Ruby used a headstock casting that doubled as a mounting foot with a bolt-on motor as part of the optional equipment. However, as the latter carried just a 2-step pulley (when a 4-step could have been specified for only a few pence extra), the speed range was severely limited. The headstock pulley was overhung, an unusual and rather brave design decision for a precision lathe where the tradition of super-accurate bearings, of hardened steel, honed and lapped to perfection, with the pulley carried between them, had been established for over 80 years. By coincidence, the same decision had been reached by the English Pultra Company on their new range of 17/50 and 17/70 models, also announced in 1946/7. In the event, Coronet found themselves up against a number of competitors including not only continental makers such as Schaublin, but also Boxford who were manufacturing two miniature precision lathes, one a beautiful 3.3" x  9.25"  plain-turning bench type and the other a dedicated capstan. 
Intended to function either as a lathe or a precision drilling and milling machine, the Ruby was mounted on a heavy cast-iron base plate formed with a post socket at one end.  With the lathe set as a drill, the bed was up-ended, dropped into the socket and held in place by a long through-bolt. The tailstock, already provided with a lever-action feed (by the simple expedient of peg passing through a slot cut through the top of the casting) was fitted with a collet-retained faceplate that acted as a drilling table - while the (optional-extra) compound-slide rest assembly could be pressed into service as a co-ordinate table for vertical milling. In order to provide the greatest versatility, the headstock was available with a choice of two cartridge spindles: one for ordinary work with an adjustable tapered bronze bush at the front and a single ball race at the back (an arrangement also used, in a non-cartridge form, on most of the Company's wood lathes) and the other, a high-speed unit, with ball races at both ends. The assembly (not unlike that used on the first Emco Unimat lathes from 1953 and resembling a bicycle hub) was clamped into the headstock by a single lever closing down a slot in the casting; hence it could be removed very easily and swapped over. With a 0.314" bore and a  5/8" x 26 t.p.i. nose thread, the spindle was designed, like the tailstock, to accept draw-in 8 mm collets.
Beautifully painted in
black ripple enamel (crackle-black, a popular finish at the time and used to denote a quality product ) and with all the locking rings and adjusters beautifully knurled, the basic Ruby retailed for 18 : 18s : 6d without a motor (for comparison a backgeared and screwcutting ML7 was first listed at 36). Complete and ready to run the price rose to 24 : 18s : 0d. A compound slide was an extra 9 : 18s : 6d, a 2.5" precision 3-jaw chuck 6 : 15 : 0d, wire collets 7s : 6d each and stepped collets 12s : 0d. Supplied as standard with each machine was the cast-iron base plate, a hand T-rest, faceplate, driving pin, collet draw-in tubes for headstock and tailstock and one pair of precision centres mounted on collets. An interesting comparison can be made between the Ruby and the German Saacke miniature universal machine of the early 1950s - through the latter would, no doubt, have cost several times as much.
Using many components of the Ruby, including the complete headstock and tailstock units and a bar-bed, the "Jewel" was arranged conventionally with small splayed feet and a carriage driven by an overhung leadscrew running down the front of the bed. A single swivelling tool slide was fitted with the whole machine looking remarkably like the larger but much cheaper and less desirable Velox from the early years of the 20th century.
All versions of Coronet miniature lathes must have been made in very limited numbers, for today they are very rare - even the contemporary Boxford Boxford miniature precision, at an expensive 175, being relatively common in comparison.
If any reader has a Coronet miniature precision lathe, or any literature about them, the writer would be interested to hear from you.
Jewel Lathe   Ruby Lathe

The very rare Coronet "Tiara" screwcutting lathe. Although details of the specification are not known, it would seem to have been a heavily-built lathe of around 3-inch centre height and 12 inches between centres. If it followed the example of the Diamond, the leadscrew would have run down the back of the bed (the handle at the tailstock end can just be seen) with, presumably, a dog-clutch at the headstock end operated by a lever protruding from a boss on the bed below the spindle nose.

Coronet "Diamond" 2.25" centre height by 6" between centres

Like the Ruby the Diamond used an over-hung pulley to drive the headstock spindle. Note the facility to rotate the headstock, the simple, single-slide tool-rest (carried on a bar that fitted into a hole at the front of the saddle) and the large-diameter micrometer dial. This example has been retrofitted with a 4-step pulley.

A Coronet Diamond in its maker's original finish

The leadscrew ran down the back of the bed



Micrometer dial on the end of the leadscrew




Diamond lathe Page 2   Jewel Lathe   Ruby Lathe


Coronet Wood Lathes Home   Miniature Precision Lathes

Coronet Instruction Literature is available, please email for details

email: tony@lathes.co.uk
Home   Machine Tool Archive   Machine-tools Sale & Wanted
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Coronet Miniature Precision Lathes
Diamond, Jewel, Ruby  & Tiara