The hardest part is measuring accurately the distances between the bolt holes. ?The way I do that is to measure the distance between?the inner edges of the holes and the outer edges of the holes using sliding jaw caliper such as a vernier, dial or digital type, then average the 2 dimensions. ?Call this Y, the centre distance for the holes. ?
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Unfortunately your trigonometry is too blurred to read - I'm guessing that the internet automatically reduces resolution when we post anything - but it looks like you have 3 equispaced holes, so the formulae for an equilateral triangle apply in order to find the pitch circle. ?Radius =?Cos 30 x Y / 2. ?(Cos 30 ?= ?0.866, near enough).
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Having drawn the circle using the radius found above, keep your dividers set at the same radius and you can then divide the circumference into 6 equal parts.
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Even numbers of holes is easier - just measure the spacing of the holes across the diameter. ?Mark the centre of your fist hole, draw a line from this through the centre, extrapolating to find the opposite one, then for 4, bisect from the 2 centres at the vertical positions to find the 2 at the horizontal positions. ?For 8, bisect again. ?For 6, proceed as though for 3.
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Eddie
