cnc for marble

[Rufe0]

The problem is at 3m long your going to need quite large screws so that they aren't flopping & wipping around. Large screws generally have a large thread pitch, plus you'd want to use a large thread pitch anyway for rigidity. With a thread pitch of say 20mm your only going to get steps accuracy/resolution of 0.1mm with a stepper motor(with no gear reduction). Which may or may not be OK in terms of accuracy but it means the slow speed movement of the machine would be horrible. So I would suggest you find a way to gear it down or use whatever system to achieve a high resolution. 0.001mm would be good I guess. That would make slow feeds very smooth.

In terms of the machine design I'm sure we can help you design a machine that will be alot more rigid. Do a drawing and we can comment on it. Firstly you need atleast 2 rails per axis, 2 carriages/bearing blocks per rail and 2 screws per axis. I recommend you use thick wall steel box section tube for the construction, however some parts may need to be even heavier duty and so may need to be custom machined for you. I would recommend a dual gantry design. Large seperation between carriages/bearing blocks probably 400 or 500mm. That means you machine will have to be 2000x3500 to get 1500x3000 travel.

I assume that the marble will almost always be a similar thickness and that it won't be very thick. That is a good thing because you won't be able to have much Z travel, in fact I recommend you make it as little as possible.