#56117
david pierce
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• Topics Started: 90
• Total Posts: 1360

William,
You made a wise choice for your slide rule selection. You won’t even have to put on your reading glasses to see the numbers. Ok, here is the david pierce method for setting a dividing head. First find out the number of turns it takes the sector handle to produce one revolution of the dividing head spindle. The normal number of turns for your type of head is 40 but check and make sure. For the example I will assume that your head is 40.
1) Divide the number of divisions you want into 40. If you want 7 divisions the problem will read 40/7 = 5 5/7. Notice that I did not use a decimal for the remainder.
2) Set the number 5 on the C scale over the number 7 on the D scale.
3) Your hole patterns read 15,16,17,18,19,20,21,23,27,29,31,33,37,39,41,43,47,49. Look through the numbers on your D scale until you see an integer over one of the numbers. In this case you will see 15 on the C scale lined up over 21 on the D scale and 35 on the C scale lined up over 49 on the D scale.
4) You now have two solutions to the problem 5 15/21 and 5 35/49. This means that you will have 5 complete turns of the sector arm crank plus 15 holes on the 21 hole plate or 5 turns of the sector arm crank plus 35 holes on the 49 hole plate.
5) Set the sector arms for the selected number of holes so you won’t have to count the holes on every index.
david