Smallest of the Company's twin-column models, the modern-looking 3K - with its angular lines and neat enclosures - had a 25.5" x 18.5" (520 x 380 mm) table with a working range of 18" (450 mm) longitudinally and a maximum of 24.5" (620 mm) available between table top and spindle-nose. Side-to-side travel of the head (mounted as usual on a carriage between the upright) was 14" (350 mm). Instead of the built-in standard scales and optical readers common to many other SIP jig borers, the 3K used a combination of external rulers and feed-screws fitted with very large diameter (and almost totally enclosed) micrometer drums that incorporated the SIP automatic vernier correction mechanism. The latter was a clever, highly effective arrangement dating back to at least the early 1920s that ensured the accuracy of the complete machine was greater than that of its precision feed-screws. 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 micrometer dial. Thus, for any position of table or head, a corrected reading was automatically obtained - though care in taking the vernier reading was, of course, essential. With such equipment installed, coordinate readings down to 0.00005" (0.001 mm) were possible, though with separate auxiliary ruler scales provided to cope with rapid changes when making long-travel, coarse settings. Using the standard SIP method of calculating accuracy, the displacements of table and spindle-saddle could be held to within 0.00015" (0.004 mm). The boring capacity of this substantial machine was, at 4" (100 mm), twice that of the larger single column SIP model with recommended drilling limits of 1.2" (30 mm) in cast iron and 1" (25 mm) in steel.
Able to be moved by hand or under power, the two screws used to elevate the crosshead were completely protected against swarf and dirt and fitted with a positive lubrication system - as were the covered ways over which the table ran. The cross movement of the head-saddle was motorised for a rapid traverse (with safety knock-off switches at each side) with control of both it and the spindle feed by simple but positive-action turn-push-pull levers.
Running in the usual super-precision, SIP-manufactured ball and roller bearings, the No. 2 Morse taper spindle was formed on its outside with a SIP taper, in an appropriate size 2e, and counterbalanced by a spring, the aim being to give the finest possible sensitivity to the hand feed when drilling very small holes. Rollers and races were "specular ground" to better than 10 micro-inch (0.25µm) by a special process that eliminated the need for further finishing. The bearing rollers had their diameter and concentricity consistent to within 4-millionths of an inch (0.1µ). At the signing-off test, the maximum permitted eccentricity at the spindle nose was 0.00008" (0.002 mm) and the spindle assembly was not allowed to increase in temperature by more than 10°C during a 24-hour run at high speeds. For use in regular boring, or production work, a useful 6 rates of power feed were fitted: 0.0008, 0.0016, 0.0024, 0.0036, 0.0048 and 0.0072" (0.02, 0.04, 0.06, 0.09, 0.12 and 0.18 mm) per revolution of the spindle - safety switches being provided to knock off the power at each end of the travel. Downfeed could be measured in various ways: by reference to a ruler for a rough setting or by combining the ruler with a holder for slip gauges and a very sensitive dial gauge.
Driven by a 1 h.p. 3-phase motor, the eight spindle speeds were: 75, 125, 210, 340, 480, 770, 1250 and 2000 r.p.m. An electric coolant pump, tank and fittings were supplied as part of the standard equipment.
With an overall front-to-back measurement of 67.75" (1720 mm), a width of around 60" (1520 mm) the 3K weighed about 3900 lbs (1775 kg) net..