Thanks for that tip, Will. (I don't have a lathe.)
The drilled end of the 3/8" square bar seems plenty robust to me. I like that it avoids having an aluminum pin. I have a prejudice against aluminum bearing surfaces. The one in the photo has a brass pin in one end - to facilitate tapping screw holes into the cross rod for the knee lever cradle - and a steel dowel pin in the other. Both 1/4". They fit tight enough to require light hammering, but I epoxied them also. The rod mounts in nylon bearings.
I centered the hole just by measuring carefully. It seems to me that the concentricity is not actually all that critical. I did take a lot of care to clamp the rod perpendicular to the drill press table. My hunch is that the error is in the same ball park as the error I'd get with a lathing or annular milling process (if done in an urban tenement apartment like the one I work in). If I were doing a bunch of these, maybe I'd devise a jig that would better insure that the second hole drilled was in line with the hole at the other end (which is what's critical).
Re: hollow mills: I have a number of counterbores that act as annular mills if you leave the centering pin out. I don't have one large enough for a 1/4" pin. But maybe people shopping for hollow mills/annular cutters might want to check out counterbores too?
Jon
a different way to do cross rods!!?
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Re: a different way to do cross rods!!?
Why not just tap a hole and add a 3/16" thread allen head screw on each end? They could easily be polished to function as bearing surfaces.
Re: a different way to do cross rods!!?
A good idea Per.
Ron Mc
Ron Mc
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Re: a different way to do cross rods!!?
I have been racking my brain on how to round my square cross shaft ends on my new build, I,m sure glad I stumbled cross this posting from Wayne, I have plenty of stainless steel allen headed screws to tap in the ends. Thanks Wayne for sharing your thoughts. Rick
Re: a different way to do cross rods!!?
Kline turned his cross shafts down to 1/8",,,smaller diameter = less friction. Being that short, into a bushing = plenty strong enough. JMO