Surely unique amongst lathe-mounted milling slides this special twin-spindle Cataract unit can only have been equalled or outclassed by that available for lathes produced by the Waltham Machine Works.
Intended to tackle difficult, precision-milling jobs the device was mounted in place of the toolpost, and so had available the full range of movements allowed by the compound slide rest.
The cutter head carried two hardened, ground and lapped spindles, each revolving in adjustable bearings. One spindle carried a standard Hardinge 1C collet and draw bar, the other a No. 4 Brown & Sharpe taper. The cutter head could be swivelled and, by removing the retaining nut and inverting it on its seating , the heads made to change places.
At the driven-end of the spindle was 3 :1 gear set, with interchangeable driver and driven gears. Input speeds of 300 and 600 rpm from the overhead drive, or grinder countershaft, gave spindle speeds of 100, 200, 300, 600, 900 and 1800 rpm.