Ali T. Borahan wrote: (clip) Does it really matter if the contact point is the tangent line that's exactly perpendicular to the center of the arm? (clip) ^^^^^^^^^^^^^^ It matters not at all! The design I described in an earlier post takes this to an extreme. Instead of slots, I mount the arm through a drilled hole, with a clamping bolt. I get the distance from the centerline by swinging the arms away from center--the action the guides would prevent. I have built two steadies this way, both used on large lathes, and they work just fine.
Long before the work has a chance to start whipping, you would notice a little looseness at the wheels, and correct it. If the bolts are tight, and the work is round, that is sufficient.