Beginners screws ( was ACME ( was Re: leadscrew,

> Just want to report , that I was at Home Depot and carefully inspected
> caster wheels.
> They seem to be perfectly round to me!
> Designated them as important component of the future guideway.

You should put a dial indicator on them as they rotate. 10 thou is not easy to see by eye, but if you do things like vee routing text, that error will show up in your finished part. Roller blade wheel bearings should be available at a local sporting goods store. If I were looking for locally available solution, that's the way I'd go. I think you'll find the bearing to be cheaper than casters also.

I learned all this stuff the hard way. My table started out as a simple 2 axis plasma cutting table. After I got the table, rails and carriages built, I decided to add a Z axis to retract and lower the torch. After the Z axis, I realized that I could do some pretty cool 3D carving. It was then that I figured out that the angle iron rails did not offer much linear consisency. I made a jig to grind the angle rails and got them to within .002 which has been working fine for woodworking.

My point is that your choice of rollers will effect your Z axis accuracy. If all ytou want to do flame or plasma cut, then that is not a big deal, but if your want to carve photographs and make signs, Z axis precision is pretty important. Imagine cutting a photograph .020 deep and for every revolution of an X axis roller, the carriage floats up and down .010 because a roller is out of round.

Ross