First jig boring machine

First jig boring machine, 1921 made by Societe Genevoise D'Instruments de Physique for the Royal Small Arms Factory at Enfield

The jig-borer is a very accurately made and extremely rigid machine tool intended for the exact location and boring of holes and is suitable for use in making jigs and dies. The drilling head is mounted on a cross beam spanning the table and supported by columns in the manner of a planing machine. The head is capable of being traversed along the bridge and the table can be moved at right angles to this direction.

This machine has a capacity of 18 inches by 24 inches and weighs about 2 tons. The precision of a jig-boring machine is such that it should be kept in an air-conditioned room at constant temperature.

The jig-borer originated from the pointing machine made in 1912 by the Société Genevoise d'lnstruments de Physique, at Geneva, for marking out watch plates. This led to the design of the industrial jig-borer of which this, the first made by the company, was built in 1 921 for the Royal Small Arms Factory at Enfield. In the meantime the Pratt and Whitney Company had brought out a jig-boring machine in 1917.

The lateral movement of the boring head and the movement of the table are controlled by lead-screws, set by micrometer drums. A pitch-correcting device rotates the vernier sector, by which the setting of the micrometer drum is made, by an amount which eliminates the error at the position in which the table or the head is being set. The amount of rotation is determined by a lever, in the ratio 200:1, in contact with a metal template. The template was made for each lead-screw in terms of a high precision scale read with a microscope at one centimetre intervals. The guide ways of the bed are slightly convex in order to correct for the deflection produced by the weight of the table.