Big CNC router

Hello all;
I keep putting off this project out of fear that I will end up with yet another piece of equipment I don't need. However, another four hundred bucks went down the road to a competitor this weekend. This customer appears to have an ongoing need.

We want to build a router table to handle 4'X8' sheets of .125 aluminum with +/- .005 in./ft. accuracy in drilling and slotting. Speed is not a major consideration here, as most of the work is prototype. On the other hand, the machine will later be used for cutting patterns in plywood and particle board, so we will eventually need high feedrates.

1. Should I use preloaded nuts on rolled ballscrews or are the nuts tight enough without preloading?

2. Most of the low end or home built machines use cast aluminum toolplate for the gantry. Is this preferable to a steel weldment?

3. Larken and a few others are using dual screws for the X (moving the gantry) axis. This seems like a sensible approach. Should I use a chain or belt to couple them or would dual motors be advisable? I am assuming that dual servo motors driven with G320's would reduce the chance of problems one might encounter with steppers. I am using CNCPro.

4. Is cast aluminum toolplate the best option for the table? How thick? MDF would not work with coolant.

We have about $6,000 in the budget for this machine.

Doug


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