I'm building a CNC impact engraver for engraving anodized aluminum, plastic, and maybe some other materials. The idea is a cross between the handheld vibratory engravers and a dot-matrix printer. It works like a dot matrix printer, except it produces small pits in the material instead of applying ink.
The travel will be about 30x20" depending on the slides I find. Either way, it is larger than any other cnc impact engraver I'm aware of.
Anyways, I'm trying to decide on the drive system. The machine looks like a typical gantry cutter. My idea is to use a toothed belt drive to move the gantry and cross axis. The gantry would have a belt on each side to keep it perpindicular to the slides. The belts are what dot-matrix printers use, and it seems to work well to get the required resolution, but I am wondering about using ball screws instead.
The resolution would be in the 200-400DPI range, so the tolerance would ideally be around 0.0025". Realistically, as long as it too far from that, it should produce nice engravings. I would be engraving equipment faceplates, computer cases, etc... so it doesn't have to be perfect since it will be viewed from a few feet away.
Would ball screws be worth the extra cost for this, or would the belts work well? I'd like the machine to be under 800$ (which it would be with belts), but its more important that it work. Another option is to make the gantry ride on a rack and pinion.
I might be able to add a linear encoder later if high precision is required (as is also used in some printers).
I always lean toward rack and pinion drives. They are very stiff, have good accuracy, and can have zero backlash. For an engraving application which you describe, you could drive the long axis with a common cross shaft having pinions on each end to engage the two racks. There are a lot of positives for rack and pinion including cost and ease of application.
I forgot to mention that I have a 32 x 36 (3) axis table, .001 resolution, which would work "right now" for your application. I could send you pix if you like, or doa sample "engraving" using a very fine line pen if you want to send me the G-code for a sample engraving.