Ok, I confess, I've caught the bug and I have to have a CNC router. What I want to do here is to go over some of the calculations I've been doing. The idea is basically collect a bunch of back-of-the-envelope calculations to direct the design decisions. Hopefully we can get a handle on the strengths and weaknesses of the design and build it up or pare it down accordingly.
Here are the design objectives (in no particular order):
1) Cheap, hardware store style router. All components should be easily sourced from the internet or from local stores. Shouldn't require any non-diy type tools to build, i.e. no welding, milling, or turning. Ideally just a circular saw/table saw and a drill.
2) It should be super rigid, doesn't have to be especially strong. This is a hobby machine, so machine speed isn't of the essence the way it is in a production environment. If the loads are too much for the strength of the frame, then just slow down the motion, take a lighter cut, etcetera...
3) It should be very precise, but doesn't have to be especially accurate. Basically the motion should be very repeatable, but doesn't have to be spot on relative to all the other points on the table. The idea here is that accurate components cost mucho bucks, and require lots of work to assemble and tune. On the other hand, this thing is being driven by a computer which can easily distort the toolpaths to compensate for inaccuracies in the motion. So let's build a precise, but inaccurate machine that can be calibrated such that the computer can make it accurate. The ideas for doing this will probably be posted in a separate thread.
Since it is much easier to talk concretely about a specific machine, here's a pic of what I have in mind. It's a typical moving gantry style router along the lines of JGRO's or Joe's. Cutting volume is 48" x 24" x 5", which should allow for a wide range of possibilities. The frame is constructed of Unistrut, which I arrived at after considering MDF for a long time.
I'd love to get some feedback on the calculations. The trouble with quick calculations is that you invariably assume certain things, which may not turn out to be true in reality. Hopefully some of you experienced CNCers out there will spot the problems.
Cheers, -Russ