An Operation & Parts Manual is available for the Ainjest
Manufactured originally by Saunderson & Costin Ltd. in Highclere near Newbury in Berkshire, the Ainjest "quick-threader" was a long-time favourite in production and jobbing machine shops. Bolted and dowelled to the right-hand face of the apron, it was intended to replace the ordinary screwcutting mechanism of almost any lathe in the 5 to 9-inch centre height range and, with both metric and inch versions available, transformed the normally rather laborious thread cutting process into one that was both simple and quick. Typically, using tungsten-carbide tooling, it was possible to cut a 2-inch diameter 12 t.p.i thread at a spindle speed of 1200 r.p.m. in just four passes. Equipped with its own leadscrew half-nut and engagement mechanism, the use a dial-thread indicator and the need to visually monitor progress were both rendered superfluous - it being possible to cut threads tight to a shoulder and into blind holes at high speeds in complete safety. Once set up, all the operator had to do was press down on the engagement hand, the drive engaging automatically at the correct point - even when cutting fractional threads. Threads could be generated by either the straight-in or half--included-angle approach, though in the latter case allowance had to be made for the fact that the tool would have moved forward by half a pitch at the end of the cut. Fitting the attachment did not interfere with a lathe's normal operation and it could be brought into operation within a few seconds - though obviously a careful reading of the instruction manual was a prerequisite for complete success….