CNC router for wood processing

[ademenev]

I am planning to build a router for wood, with occasional machining of some aluminium parts. I have plenty of time before I will be able to actually start building the machine, so I though it would be a good idea to start a thread to gather opinions and advise from more experienced CNC builders.

The build is going to be based around the parts I already have at hand:

• 2x 1400mm linear rails
• 2x 800mm linear rails
• 2x 350mm linear rails
• 1x 1400mm ball screw
• 2x 800mm ball screws
• 1x 350mm ball screw
• 2.2 kW water cooled spindle
• 4x NEMA23 steppers

All screws are 1605, the rails are 20 mm rectangular, 2 slider blocks per rail. X is going to be the longest axis. One reason is that I want 2 ball screws on Y axis, and the other is that this configuration better fits my planned workshop layout.

Materials:

• all steel
• 80x4 square tubes for frame and gantry, smaller tubes for base (possibly filled with concrete or sand )
• 4 - 5mm thick steel for plates, gussets, brackets and similar parts

Goals and requirement:

• simple power tools. Angle grinder, MIG welding machine, hand drill, possibly a very basic drill press. No machined parts
• aiming for 0.1 mm precision across whole working area
• fast axis movement would be nice, but precision is much higher priority
• the design should include 4th (rotary) axis, although I will be building it only after the 3 axis machine is complete

Given the precision goal, I need to provide means for aligning the rails. I am thinking about using set screws as shown in the pictures below



After the alignment is done, I can pour epoxy to permanently fix the rails (oh, how do I prevent leaks through holes in the tube?!). This will allow me to precisely align the rails in up-down direction, but I will have to tolerate any inconsistencies the rails may have in left-right direction. Also, X axis will need both rails mounted on the same plane (front of gantry) instead of mounting one in the front and one at the top. That is probably OK.

I have also seen people pouring resin into interconnected channels built around rails supports, and then mounting the rails on top of resulting surface. Intuitively, set screws allow for more precise alignment, but maybe I am wrong.

For me, the alignment approach is the fundamental decision I have to make before I start designing the machine, so that's it for now. Comments and advise are highly appreciated