SIP Jig Borers of the 1920s
No. 2C and No. 3
Société Genevoise d'Instruments de Physique
Operation & Maintenance Manuals are available for most SIP Jig Borers
SIP Home Hydroptic 6A & 7A Jig Borer 1-H Jig Borer 2P
Jig Borer 3K Jig Borer 4G Jig Borer 5E Jig Borer 8P
Accessories Jig Borers 1920s No. 2C and No. 3 Tooling Cabinet
According to a book published in 1954 by Société Genevoise d'Instruments de Physique "As Ninety Years Went By, 1862-1952", the Model MP4 was the first industrial purpose machine built by SIP in 1921, and the first of its kind to be able to precisely locate and bore a hole. This was superseded, in 1923, by the MP5, a slightly larger machine - however, the smallest and cheapest model in Company's twin-column range of the early 1920s was the SIP No. 3, a jig borer intended as both an economical purchase for smaller machine and tool-making shops and for use in manufacturing plants. As a lighter model its work capacity was somewhat limited, it being able to drill a 1-inch (25 mm) hole and bore up to 4-inches (100 mm) in diameter - both in hard steel - and drill a 1.5-inch hole in cast iron. However, despite the lower price and specification, accuracy was not compromised, the makers guaranteeing that the maximum error in distances between the axes of bored holes would not exceed 0.0006" (0.015 mm), that holes bored and finished with a fine cut would be cylindrical and true to within 0.0004" (0.01 mm) and the accuracy of displacement of table and cross slide would be 0.0002" (0.005 mm).
Intended to be run from a motor bolted to the frame, it could also be powered from a flat belt connected to an overhead line shaft. Four spindle speeds were available - a rather slow set of 75, 150, 300 and 600 r.p.m. - driven from a 4-speed gearbox with an integral friction clutch
With three longitudinal T-slots 1/2" (12 mm) wide, the 16" x 24" (400 x 600 mm) table had a travel of 16 inches (400 mm) with the head able to be traversed through 12 inches side to side on the cross beam (though an additional 43/4 inches (120 mm) of movement available to the left to allow the removal and insertion of tools when working with extra thick jobs. All feeds on table and cross beam were by hand. The machine could be supplied to metric or inch specifications with the former having 5 t.p.i feed screws and the latter ones of 5 mm pitch. The huge micrometer dials (even on these early models, almost fully enclosed as a precaution against damage) graduated to 0.0005" (0.01 mm) and with vernier scales reading down to 0.00005" (0.001 mm) - incorporated the novel SIP auto-correction mechanism. After the machine was assembled, any errors in the movements of table and cross-slide were assessed with great accuracy by comparison with a standard scale of a type similar to those prepared for use in National Measuring Laboratories. A "curve of errors" was prepared and reproduced, in an enlarged form, on a strip of hardened steel, fixed to one edge of the table and work-head slides. As the slides moved, a small lever followed the strip's profile and transferred its movements, via a long rod held in brackets, to a lever at its other end connected to a sliding vernier scale secured next to the rim of the feed-screw
With 6.5 inches (165 mm) of travel, the No. 3 Morse taper spindle could be moved so that its nose was a maximum of 12 inches from the table, allowing jobs up to 8-inches thick to be mounted. In addition to a hand-driven down-feed, power was fitted, the three rates of feed (selected by a quadrant lever) being driven through oil-immersed helical gears at the rate of: 0.003, 0.005 and 0.008" (0.08, 0.13 and 0.21 mm) per revolution of the spindle.
51-inches wide, 57-inches deep front to back and standing about 72-inches high (1230 x 1450 x 1815 mm) the No. 3 weighed approximately 2550 lbs (1150 kg).
Built as a "single-column" machine the SIP No. 2C Jig Borer had (like the modern 2P) a motor mounted at the rear of its head. Little is known about this model save that the design of the table and its ways was unusual. With the head fixed and unable to be moved fore and aft, the table was arranged to sit on a casting carried on two slightly elevated wings formed as part of the main body casting and running at each side of the upper column section that carried the head.
If you have an early SIP jig borer, the writer would be interested to hear from you..