Machining Cylinder Fins
Special-Purpose Maxicut Lathe for Aero-Engine Work

One of the problems connected with the manufacture of air-cooled aircraft engines is the economic machining of the cylinder cooling fins (Fig. 1); usually, the sides are tapered and the depth varies to provide equal expansion throughout the length of the cylinder. In the case of the Hercules engine, one bank of fins is eccentric with the cylinder bore. The methods employed by different firms in both Great Britain and abroad, described from time to time in this journal, consist of either turning the fins with packs of narrow tools (Fig. 2) or plunge-grinding with banks of wheels. Some idea of the difficulties encountered may be seen from the Hercules cylinder, which has an eccentric bank of 19 fins with a concentric bank of 20 on each side, giving a total of 59 fins approximately 1.25" deep, the fins are tapered on both sides.

Fig. 1. Section through the cooling fins of an aero-engine cylinder barrel. Note the tapered form and varying depth of the fins.	Fig. 2. An earlier type of tooling for cutting 40 concentric fins in the Hercules cylinder barrel. There are 78 separate tools, each with a ground and lapped tungsten-carbide tip. Very similar tooling is employed on the Maxicut lathe.	Fig. 3. The Hercules cylinder barrel, which has two banks of 20 fins concentric with the bore and one bank of eccentric fins in the centre.