wrote in message
...
Recently I had a customer ask me to adapt a toothed belt pulley to
a hub with a tapered bore. The hub fits a Bosch magneto from the
late
twenites or early thirties. Apparently Bosch and other manufacturers
made magnetos for cars at least as far back as 1905. This mag is
going
on the customer's model A Ford.
The hub had 3 keyways broached in it and all were undersize for
modern woodruff keys, and the mag is milled for a woodruff key. So I
needed to broach one of the keyways to size and needed a tapered
broach guide bushing to do the job.
I started to measure the tapered bore angle when I decided to see
if the internet had the answer. What I found was a scanned
transcript
of a 1905 meeting of the SAE where they discussed several subjects.
One of these subjects was the fact that mags made for 6 cylinder
engines had a different taper than those mode for 4 cylinder
engines.
It was proposed and then decided that the new standard would be for
all mags to have a 5.75 degree taper, the taper that the 4 cylinder
mags used..
So I made the bushing to 5.75 degrees and it worked perfectly. I
just love the internet.
Eric

Good hunting.

Keys can be milled thinner too, or offset to adjust timing:
https://bikemanperformance.com/bmp-o...ming-keys.html