Originally Posted by
oneclick
I'd use wood if I had to, but
Sounds like you have not used wood blocks, so I thought I'd respond with my own experience.
a) wood is softer and weaker than aluminium - I'd expect that the bearing surface would get marked/damaged/distorted easily; would have to make (an)other pair(s) of blocks;
I've made blocks out of dogwood, a hard resilient woods that worked well for rolling with none of the damage you mention. If I were to make another set, I'd use Lignum Vitae, which I didn't have on hand at the time. LV is twice as hard and used for shaft bearings on ships.
b) lubing/friction will be less consistent with wood than aluminium;
Why would this be?
c) hole saws do not cut accurate or smooth holes (not even Forstner bits). They are meant for making holes that you put something like electrical wiring or heating pipes through - clearance is the goal, and 1/8 inch bigger than nominal size is no problem; and
I used a forstner bit in a drill press. Accuracy is a function of your equipment, not the material.
d) if you don't get the saw split at exactly 1/2 you will have problems getting one of the block pairs around the tube; better to get two blocks with flat faces and bolt them together before making your hole - the centre-line will help keep the drillbit in the middle. (If you are boring the hole this should not be a problem, but drillbits sometimes go where they want to, not where you want them to.)
I agree that it better to clamp 2 halves and drill down the center (and you really have to use a drill press with the blocks held firmly). A thin saw kerf shouldn't be a significant issue with careful clamping on the frame tubes since it's the nominal radius of the hole that matters.