Thread: my build from the start
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.
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
3 stud PCD= S/0.866
The Following User Says Thank You to ptjw7uk For This Useful Post:
thanks peter star man, added it to the post :-)
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).
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.
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.
The Following User Says Thank You to Jonathan For This Useful Post:
thanks jonathan ;-)
Ahh just realised. My method can easily be extended to the general case for n bolts. You just need to know half the angle interior angle of the particular polygon. Then do cosine of that to get the factor...
3 = Triangle, 60/2 = 30, so cos(30)
4 = Square, 90/2 = 45, so cos(45)
5 = pentagon, 108/2 = 54, so cos(54) = 0.5878 (!)
6 = hexagon, 120/2 = 60, so cos(60) = 0.5
The formula to find the interior angle is 180(n-2)/n.
So that means, given n bolts with spacing x.
PCD = x/(2*cos(90(n-2)/n))
Last edited by Jonathan; 02-01-2011 at 03:49 PM.
like the formulae but...
er where is x used??there are 10 sorts of people in the world
them as understand binary
and thems as doesn't
x=bolt spacing(centre to centre)
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