It is not often that a piece of specialist equipment escapes from a precision instrument company (such items are often destroyed to deny potential competitors any advantage) but this S.A.D.A.M.E.L. "Type 4" jig borer has proved to be an exception. Manufactured by the Sadamel Company of La Chaux-de-fonds, Switzerland - a firm still in existence making automatic ticket machines and similar products - the borer is little known and infrequently encountered. Designed for use in watch factories (the example illustrated is thought to have come from the Bulova in New York having been imported by another now-defunct company called Alina) the Type 4 was described by its makers as a "Jig Borer and Measuring Machine" and, protected in a temperature-controlled tool room (and so secured from those tempted to use it for other than its specialist tasks) was reckoned accurate enough to make use of enormous 4.3-inch diameter vernier-scale micrometer dials that allowed the 0.001-inch marks to be set approximately 0.140 inches apart and hence the vernier scale to read off settings with an accuracy of 0.00005" (five one-hundredth thousandths of an inch). . However, the present (very experienced) precision-engineer owner of the machine (illustrated on this page) believes the claimed level of accuracy may be open to question. For coarse positioning precision rulers was set into the base casting just below the table's front face and on the side of the horizontal ram. To protect the dials from damage each was encased, with a small aperture at the top to take readings, in a semi-circular metal housing. The heavy 15" x 57/8" table carried 2 T-slots, had 8 inches of longitudinal movement driven by a 3/4-inch diameter feedscrew with a 10-t.p.i 60-degree thread.  The table, which ran on a base with ways machined as one inverted V and one flat, was designed to run with absolute smoothness and to achieve this was held in place by just the feedscrew and its own weight, there being no dovetail edges or adjustable gib strips. Of course, before boring began, the table had to be locked in place and a powerful clamp was provided for this purpose. If the readings from the dials were as accurate as claimed, the machine would have been very useful as a two-dimensional comparator device, being able to check, for example, hole-centre distances, progressive and periodic errors of thread pitch and tapers by simply attaching suitable pointers and reading from the scales.
The vertical head, fitted with a lever-action quill to accept 8mm watchmakers collets and with a supplementary coarse feed by a small, un-calibrated handwheel (connected in the manner of a microscope rack), was mounted on a wide, 6-inch travel ram running, as did the immediate forerunner of the jig borer the SIP watchmaker's pointing machine of 1919, in "sunken" V- ways. Like the table, it too was devoid of any retaining dovetails or adjustable gib strips with a clamp to lock it once the settings had been achieved. The head ran up and down two inverted V ways and could be adjusted to come within  2 3/4" of the table or moved as far as 71/2" away; it accepted a number of interchangeable fittings that could be simply slid in and out: a centring microscope with cross hairs, a "sliding centre" (to enable the accurate positioning of pre-drilled work) and a quill able to accept 8-mm horological collets - the quill travel of only 1.5 inches being a reminder that this was machine designed for the production of jigs and fittings used in the watch and instrument industries. A quill depth-stop was supplied and this, running on a 1-mm pitch screw, carried a metric-graded graduated dial - one hopes the operator was mentally agile enough to accommodate the switch from inch units on the table.
The operation of the down feed was interesting: the spindle assembly, sliding in the head, weighed 3.3 lb and was normally supported in its uppermost position by a swing-away stop. The spindle was lowered towards the table by gently supporting the lever arm, one finger beneath
it being sufficient to ensure a very light contact with the workpiece - an essential feature when using miniature drills. Rather unusual and very delicate.
The jig-borer was fitted with a form of variable-speed drive using a vertically-mounted 3000 r.p.m 230-volt motor connected to a "tube" - and so almost certainly of DC configuration. In order to obtain a constant belt tension as the head moved up and down and in and out a rather complex drive system was devised with the motor connected to a vertical drive shaft the top section of which carried a long, spring-loaded arm and a round-belt pulley that took the drive out to a tall, vertical, flat-belt pulley that in turn passed the drive across to the spindle head. Whilst the spring-loading of the arm held the flat belt tight the drive to the spindle itself passed first through a small aluminium-cased 3 : 2 reduction gearbox, so relieving the spindle and its super-accurate bearings of any sideways loading. With the pulley system gearing up the maximum motor speed to become 4075 r.p.m at the input to the gearbox (and with the 3 : 2 reduction allowed for), the spindle speed range would have been from a few rpm above zero to 2700.
If you have a Sadamel machine tool, or any literature about them, the writer would be very interested to hear from you..