[Alex van de Wetering]

Time for a new update. The chainwheel is done in the meantime. Here is a short description of the process:

There were two issues with the newly cut BSA chainwheel; it's is a few millimeters too big (while the centre is of the correct size) and it's completely flat, compared to an original chainwheel which is slighly pressed into shape, creating an edge to guide the chain onto the teeth.

To create the correct shape and size of the chainwheel I decided to use the cranks and the teeth of the stuff that came with my bike and the centre of the newly cut BSA toothwheel.
I fixed the newly cut wheel to the "modified" crank (rounded to the BSA shape) with two small welds. This way I could check if it was centered and straight, before securing it.
After checking, I made a ring of welds "filling" the gap between the hole in the chainwheel and the slightly smaller crank. After cleaning up the welds I welded some extra material to the centre to get it a flat surface in the centre.
A normal chainwheel has a boss near the centre, which is basically some material from the crank which is forged around the hole in the chainwheel. It also ensures the chainwheel positions good on the bike itself. I replicated this by welding a thick washer onto the chainwheel. Four holes were drilled to be able to weld it securely to the chainwheel.