On Sun, 02 Oct 2005 15:37:28 GMT, Bruno wrote:

wrote:

I need some guidance on figuring out what the bolt hole co-ordinates
are to build a drive flange. The hub I need to bolt to has three
holes, evenly spaced with a center to center dimension of 3.607. How
do I calculate what the bolt hole x-y co-ordinates are to drill this
when held in the mill vice? thanks in advance, ron

No trig needed on this one...

I assume an equilateral triangle... the holes at each point at 12:00,
4:00 and 8:00. Based in the center of the bolt hole pattern, I first
calculated the triangle for the 4:00 hole by drawing a triangle with
the hypotenuse as the line from the hole to the center. It's a classic
30-60-90. We know the X value is 1/2 the hole to hole distance (3.607
/ 2 = 1.8035). Divide that by sqtr(3) gives the Y coordinate. The 8:00
hole has the same Y and negative X coordinate. For the 12:00 hole, I
make another triangle with the hypotenuse from the 4:00 hole to the
12:00 hole. Another 30-60-90 where the height is 1.8035 time sqrt(3)
and then we subtract out the Y of the other holes to get the Y off
center.

So, the coordinates based on center are...

0, 2.0825
-1.8035, -1.04125
+1.8035, -1.04125


-Bruce

Oops. Bruce is right. I use a bolt circle of 3.607 dia rather than
center-to-center distance of 3.607.