I just about have the needed parts to start assembling my machine.
Here's what I've got:
2 ground screws(they seem to be at least) and 1 rolled screw. No backlash, accuracy between ~0.0003"/12" and 0.0005"/12".
2 pairs of THK linear rails, 26"-SR25s(overkill) and 14"-SR15s, and one SR35 48" pair of NSKs (super overkill)
quite a bit of 8020 3030 stock (3"x3")
I have reason to believe that the heavy duty 8020 aluminum extrusion will allow for repeatible cuts for wood and aluminum at slow speeds, but here are a couple of my concerns about accuracy.
I am assuming that the rail pairs are straight and dimensionally identical. However, even the best stuff coming off of manufacturing line at 8020 is not going to be exactly square or identical (i.e. 3.0001x3.0004 at one end, 3.0000x3.0007 at the other), and these are the pieces onto which the rails are fastened to. Sort of like tossing a ferrari engine into a pinto. So, this automatically tosses the 0.0005"/12" out the window. Due to using this type of framing for the whole structure, I now have error all over the place. welcome to the real world, I guess. AND, This is heaped on top of my own human error when mounting the rails!
What can I do to minimize this?
1) Have the framing mounted together on a milling machine and have the tops surfaced together?
This seems to be the best solution, although this could get expensive.
2) Assemble the machine and use trial and error, using depth guages, micrometers, etc to adjust the machine. making depth cuts at the extremities of the machine's cutting envelope in order to get feel for how the rails are skewed, and the them use thin shims to gradually bring the rails into the same plane. Do this for each axis.
thanks for any suggestions.