Dividing Head Question

Actually, 2º 10' is equal to 130' and 360º is equal to 21600'. Dividing the former into the latter give exactly 166.153846153846 divisions, according to Excel. (Bob, you got caught in rounding error)

However, the question was how do you set up a dividing plate to produce a rotation of 2º 10' (+/- 5 ", the typical resolution of a rotary table)?
 
RJSakowski said:
Actually, 2º 10' is equal to 130' and 360º is equal to 21600'. Dividing the former into the latter give exactly 166.153846153846 divisions, according to Excel. (Bob, you got caught in rounding error)

However, the question was how do you set up a dividing plate to produce a rotation of 2º 10' (+/- 5 ", the typical resolution of a rotary table)?
Click to expand...
Well, a standard B&S dividing head does not do differential indexing, and 166.153846153846, even if 166 divisions can be done, will not be within the 5" tolerance. Perhaps on a differential indexing head, with all the attachments, but I think this confirms that the dividing head is not equal to the rotary table for the randomly stated sample angle. And that is what I had guessed. If the boss told me to make it with the dividing head, my answer would have to be "not with the tooling on hand."
 
Insubordinate employees always give me headaches.
 
RJSakowski said:
Actually, 2º 10' is equal to 130' and 360º is equal to 21600'. Dividing the former into the latter give exactly 166.153846153846 divisions, according to Excel.
Click to expand...
Well, likely not "exactly." Notice that the long number has repeating groups of 5 digits after the decimal point. That will repeat on and on, never reaching an end. Still, close enough for anything we are doing by calling it 166.15 divisions. Measure it with a Moore Special Tools rotary table, mark it with a carpenter's pencil, cut it off with a hardy (hardie) and a hand sledge.
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Bob Korves said:
Well, likely not "exactly." Notice that the long number has repeating groups of 5 digits after the decimal point. That will repeat on and on, never reaching an end. Still, close enough for anything we are doing by calling it 166.15 divisions. Measure it with a Moore Special Tools rotary table, mark it with a carpenter's pencil, cut it off with a hardy (hardie) and a hand sledge.
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Click to expand...

Good catch, Bob. I didn't notice the repeating sequence. When I used Excel to do the math, I set the number of decimal places to the maximum which was 30 decimal places. It gave all zeroes after the 12th decimal place and the implication was an exact answer. Apparently, Excel has rounding errors too. :idea: To put things in perspective though, a 5 second error in laying out an agle would amount to .00012" on a 5" radius.
 
To turn the dividing head 2 degrees 10 minutes, a 54 hole dividing plate should get the job done. with a 40:1 reduction
13 holes out of 54 holes is 360*13/54 = 86-2/3 on the dividing plate, 2-1/6 on the head.
Not the easiest way to get there, but It would work.
 
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