I've accepted the fact the I am eventually going to have to build a cnc mill from scratch, not because I need another mill (got a cnc'd taig), but because i need to design and build something else (mechanical engineering student, classes and theories and no application is driving me crazy)
I'll present my general ideas and some questions that i have and would very much appreciate any helpful input. I want something that can remove material at over 2x the rate of my taig with .005 accuracy and virtually no backlash
LM
I have pretty much decided on thk blocks/rails and C7 ballnuts with a zero backlash set-up, hopefully with screw mapping i can get my acuracy down to .001". What are the pros/cons of preloaded vs dual ballnuts?
Rigidity/Frame
I am thinking a steel tubing weldment c-pillar. I considered epoxy granite but it seems much easier to build a square rigid frame out of steel. The rigidity ofsteel is going to help my capabilities more that the vibration reduction of epoxy granite right? Hopefully i can get the rail mounting surfaces ground flat and the mounting holes precisioned with a HAAS here at school. That and precise squared angles gives me a great frame right? I also considered simply filling the tubing with e/g, but the steel will much more thermal expansion that the steel... so i think that's out... what are some other options?
Spindle/Motor
Completely unsure, if i am beefing up everything else i guess i should get a beefier spindle, any suggestions?
I have access to welding supplies and a fixture table, so it shouldn't be to hard to precisely jig up and weld the frame it shouldn't it? My taig is 2.5x3/16 square tubing and i want considerably more rigidity so 4x.25 should do nicely shouldnt it? I will do deflection analysis on my design before i buy materials... I am not oversimplifying the process am i?
I know i need angular contact bearings. I am pretty sure i need doubles (or 2 single, if theres any difference?) But when I look for bearings they are either $10 products that dont mention accuracy or $200 precision grade. There has to be a happy medium. How much should i be paying for bearings? Can i get good bearings for less than $50/axis? If so,where?
I have though more into it but i need to hit the sack for tonight. Any input would be greatly appreciated. Thanks