I'm cutting gears ('wheels' to the horologist) for a clock. So far they have been of tooth counts that make it easy to perform the indexing with the rotary table. However, I will have to make a 21 tooth escape wheel, and 21 divides into 360

17 1/7 times. I'm prepared to makke a 21 hole indexing plate if need be, but I got to thinking about how accurate one could be just using the rotary table. Here are my calculations:

Wheel diameter: 2 inches.

RT is calibrated to 2 minutes, with a vernier to get to 10 seconds.

By eye, I believe I can come within 1/2 minute without even using the vernier.

So how accurate is 1/2 minute? If the circumference is 3.141 x 2 = 6.282 inches, then there are 6.282/360x60 inches/minute of arc, which comes to 0.291 mils/minute,

or .145 mils/half minute.

If I haven't blown the math or made any dumb assumptions, then I'm thinking that I can easily be as accurate indexing with the RT as I can making a plate. I'm not at all sure I can drill to .15 mil precision.

Any thoughts?

17 1/7 times. I'm prepared to makke a 21 hole indexing plate if need be, but I got to thinking about how accurate one could be just using the rotary table. Here are my calculations:

Wheel diameter: 2 inches.

RT is calibrated to 2 minutes, with a vernier to get to 10 seconds.

By eye, I believe I can come within 1/2 minute without even using the vernier.

So how accurate is 1/2 minute? If the circumference is 3.141 x 2 = 6.282 inches, then there are 6.282/360x60 inches/minute of arc, which comes to 0.291 mils/minute,

or .145 mils/half minute.

If I haven't blown the math or made any dumb assumptions, then I'm thinking that I can easily be as accurate indexing with the RT as I can making a plate. I'm not at all sure I can drill to .15 mil precision.

Any thoughts?

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