I was thinking 12 since it's evenly divisible by both 3 and 4 and I have 3 and 4 flute end mills - and a rotary table (7.5 turns per 30° at
90:1) . It's raining here again and I have no other projects ... except the neighbor's SxS UTV , and I ain't working on it in the rain . So a little while ago I started roughing stock for this project . Yesterday it wasn't raining , but I wanted to watch the guys installing my new septic tank . Concrete this time , the last one was steel and only lasted about 18-19 years . Snag
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Manual indexing is a tedious and error-prone task. You can double-check by setting dividers to the spacing of the first two holes and using them to confirm the next drilling location if you are interrupted. Any error should be large, a whole or half turn. My last dividing job was cutting a 68 tooth gear and there were issues... The one before that was 13, to spline a shaft for a motorcycle drive sprocket.
That storm may be heavy snow or ice when it arrives here, 'tis the season. I finished prepping for it an hour ago. jsw