Thread: my build from the start
-
02-01-2011 #51
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.
-
02-01-2011 #52
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
-
02-01-2011 #53
-
02-01-2011 #54
3 stud PCD= S/0.866
peter
-
The Following User Says Thank You to ptjw7uk For This Useful Post:
-
02-01-2011 #55
thanks peter star man, added it to the post :-)
-
02-01-2011 #56
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.
-
The Following User Says Thank You to Jonathan For This Useful Post:
-
02-01-2011 #57
thanks jonathan ;-)
-
02-01-2011 #58
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.
r=x/(cos(90(n-2)/n))
PCD = x/(2*cos(90(n-2)/n))
enjoy!Last edited by Jonathan; 02-01-2011 at 04:49 PM.
-
02-01-2011 #59
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
-
02-01-2011 #60
x=bolt spacing(centre to centre)
Peter
Thread Information
Users Browsing this Thread
There are currently 1 users browsing this thread. (0 members and 1 guests)
Similar Threads
-
Well here we go again, start another build
By D-man in forum Gantry/Router Machines & BuildingReplies: 5Last Post: 22-01-2014, 09:59 AM -
Build log when to start posting on this site
By ramsbury in forum General DiscussionReplies: 6Last Post: 15-01-2014, 10:43 AM -
NEW MEMBER: Hello all, finally ready to start a build log.
By Iwant1 in forum New Member IntroductionsReplies: 11Last Post: 25-12-2012, 06:03 PM -
A few questions before I start my build
By eclassic in forum General DiscussionReplies: 0Last Post: 11-07-2011, 10:54 PM -
NEW MEMBER: Were do I start?!
By tonygagey in forum New Member IntroductionsReplies: 4Last Post: 07-08-2010, 07:55 PM
Bookmarks