On Fri, 22 Apr 2005 15:57:58 -0700, Eric R Snow wrote:

On Fri, 22 Apr 2005 20:53:42 GMT, (Marvin
W. Klotz) wrote:

On Fri, 22 Apr 2005 20:47:42 GMT, "William Graves"
wrote:

If you place a plate of thickness, t, between one jaw of a 3-jaw chuck and
now bore a hole,
what is the offset of that hole from the center of the original rod
(diameter, D).

One source says it is 2/3 of t. This might be = 1 / (1 + cos 60 deg) but I
failed to derive this with trig.

Anyone know how to derive this mathematically?
Anyone know if this is true?

thanks
-- - - - - - - - - - - - - - - - -
Bill Graves RKBA!



The formula is a good bit more complicated than that. Take a look at the
ECCENT.ZIP archive on my website for a program that implements the correct
formula.

Regards, Marv

Home Shop Freeware - Tools for People Who Build Things
http://www.geocities.com/mklotz.geo
Greetings Marv,
Thanks for the posting. Years ago my boss and I tried to figure out a
formula to figure out how much the offset would be for a certain sized
shim in a three jaw chuck. Neither of us being math whizes didn't
deter us. Nevertheless we never did figure out and exact way to
determine the offset. I made up a chart from actual measurements but
I've been bugged for a long time about this problem.
Cheers,
Eric

It's a lovely exercise in trigonometry...

For the benefit of folks who want the actual formula:

w = width of chuck jaws
d = diameter of workpiece
e = required eccentric offset
r = d/2
root3 = sqrt(3)
p = required packing thickness

if (w root3*e)

{p=1.5*e}

else

{p=1.5*e-r+0.5*sqrt(4*r*r-3*e*e+2*e*w*root3-w*w)}


Regards, Marv

Home Shop Freeware - Tools for People Who Build Things
http://www.geocities.com/mklotz.geo