I remanufacture obsolete spares, and one part I regularly get asked for is a 70mm OD and 50mm OD, cast iron, stepped vee belt pulley with ¾” keyed bore. Never been able to find a supplier of them. Anyway, recently found 70mm OD, double vee pulleys on eBay. So I made up a mandrel to suit the 19mm keyed bore and a vee shaped form tool, and machined one vee down to 50mm OD. It worked, but I got quite bad chatter on the tool. Donkeys years since I used a form tool so, should the tool have top rake, which would make the sides cut below centre height? Or should I go in with a parting tool first, so form tool only cuts the sides?