The Formula

SK. 1 shows a very simple example requiring to position 5 holes on a given diameter.

The formula for the X co-

(P -

X = R Cos-

N

where

R equals the radius (that is PCD/2)

P equals the hole number, e.g. 1, 2, 3, 4, 5, etc.

N equals the number of holes, 5 in this case.

Similarly for the Y co-

(P -

Y = R Sin-

N

Calculating these values, even when there are many more holes, will not be that arduous if you have a calculator having trigonometrical functions. Unlike printed tables, that normally list values up to 90 degrees, a calculator will deal easily with the angles above 90 degrees, giving the value and whether it is positive or negative. I would suggest therefore that, with simple scientific calculators being available quite cheaply, one should be a standard item in the home workshop. Even better though, it is likely that your PC has one already installed, try start>programs>accessories>calculator

A disadvantage of the method in Sk1 is that it involves both positive and negative
co-

P -

X = R Cos-

N 2