my build from the start

[blackburn mark]

219.91148575128552669238503682957mm ish :)
2 x pi x r

unless iv got the wrong end of the stick

[h4ppy-chris]

3 holes around a circle 35mm apart if that helps what is the circumference ?

[Jonathan]

Erm, surely that's just 35*3 = 105mm? I've probably got a different end of the stick...

[m_c]

I get a radius of 20.207.

I'd explain fully, but I'd need to do a drawing.
It involves the constant that all the angles within a triangle add up to 180deg, and a bit trigonometry.

[blackburn mark]

ahh... i get it now, im with m_c on this one 20.07mm radius will intersect 3 points 35mm apart

took me ages to work that out

[h4ppy-chris]

i can find the formula for 4,5,6 but not for 3 :confused:

PCD Calculation Formula
3 stud PCD = S / 0.866
4 Stud PCD = S / 0.7071
5 Stud PCD = S / 0.5278
6 Stud PCD = S / 0.5

[ptjw7uk]

3 stud PCD= S/0.866

peter

[h4ppy-chris]

thanks peter star man, added it to the post :-)

[Jonathan]

Ahh, now I understand the question! You wanted *diameter* not circumference at stated in your post.

It's just cos(30)...

Let x be side length of the triangle the three points form (i.e 35mm).

(see diagram)

Draw in lines on triangle that bisect the angles. So we've now got a smaller triangle with one side length x/2, and we know the angle indicated is 30 degrees, since it's an equilateral triangle and we've bisected the corner angle.

cos(30)=(X/2)/r
r=X/2/cos(30)
r=17.5/cos(30) = 20.2072594...
(since d=2r, d=X/cos(30))

Incidentally to help remember it cos(30) is just sqrt(3)/2 = 0.866025...
Hope that helps. You can get the other PCDs using similar methods. 4 is half root 2.

[h4ppy-chris]

thanks jonathan ;-)