Intended for both production and general workshop use, Pollard auto-reverse tappers Models, 1, 2, 4, 5, 200 and the very special 3PF pitch-feed type, were intended for attachment to pillar and bench drills and vertical milling machines. Built with mounts to fit No.1 to No. 4 Morse tapers - or with custom-made flange mounts and ones to a customer's particular requirements - they were simple to set up and use. Heavily built, the units held helical gears with shafts running in largely ball or needle roller bearings, the whole assembly being contained in a sealed housing together with the double cone-clutch forward-reverse mechanism. The range of taps that could be used rant from 1/16" to 3/4", though the makers did state that, under favourable conditions, they could be used to tap holes larger than the intended maximum for each model size.
On all models but the special 200, which used collets and was intended for very fine work at high speed, the operator simply inserted the tap into the self-centring chuck and tightened it by hand. The drill's feed handle was used to apply a light pressure upon which the tapping action started automatically. The pressure applied could be varied as necessary to drive the tap down, an operator new to the process quickly adapting to what was needed to work with small or large taps and in different materials of varying resilience. When a pre-set depth was reached - the drill's depth stop being used for this purpose - simply putting a back pressure of the feed handle caused the tap to withdraw at a higher speed than that with which it was driven downwards. If the tap jammed, or reached the bottom of the hole being tapped, the clutch would slip, so protecting both the tap and the job. It was not necessary to reverse the motor on the machine being used to run the tapper to achieve withdrawal.
If you buy one of these units and have not used one before, do practice first on some scrap material before stating on that new cylinder block for your Bugatti Type 35B….