Hi,
today I started to get serious and try my first blank.
I started by turning an M12x 1.75 pitch metric thread
with a 60° tool.
My only variation was to only cut it about 3/4 of full depth
so that there were still flats at the top.
I also spun the cross travel to 29° so that the thread cutting
was only being done on one side of the tool to stop chatter.
This worked really well and cut a very clean thread.
After several dozen passes at the same final depth, it was
very smooth to the eye and dead on concentric.
(Depth of cut was only added with the top slide not the cross
travel).
I cut a long thread so that part could be the final worm and
part could be the 'hob'.
I scored the hob section again with my dremel to make it
have cutter flutes as previous.
The blank was machined concentric previously and the spindle
fitted to the toolpost.
After hobbing I drove the worm wheel blank to the 'worm' section
of the M12 and bedded it in with cutting compound for an hour.
It ended up quite a smooth job but slightly off centre as you
can see by the pics.
The beauty of this is that I can turn it down and have another go
This diameter, again, self indexed by pure luck, no maths was
involved.
It ended up having about 275teeth and a diameter of 148mm.
Steve