I’m playing around with some ideas for a larger-format CO2 laser, looking for about 1250mm by 700mm cutting area (in pass-through, I’d like to be able to put something 4’ wide in it).
To drive Y motion, I am playing with two ideas. The first thing I came up with was a C-shaped belt loop with the gantry attached to the sides of the C, and the motor at one corner. That would be about 5500mm of belt, at which point I start to wonder if it would stretch dynamically enough to affect quality. (Also, 5500mm of 9mm Gates belt would cost over $80, so not a cheap mistake if I ended up throwing it away.) I haven’t seen this belt layout in a large format machine; I think it was used a few times by people experimenting with reprap, but I don’t think it’s ended up in successful designs.
The other option is to run a torsion rod down the front or back with a loop of belt at either side and a motor driving the torsion rod. This is a relatively common setup in 3D printers (part of the ultimaker movement, also used for stacked movements in printers like the Ender 5) and I see it also in a bunch of lasers. Picking a random example from the OpenBuilds forum with a similar size, the Vulcan uses a torsion rod setup. However, it has a dual-shaft motor in the middle, whereas I have a specific single-shaft servo motor in mind.
Thoughts on what kind of torsion rod to get that’s about 1300mm long that will be both light and stiff? I could see “whipping” being a problem. I guess I could spread a few radial bearings in blocks at irregular intervals (no two on low-order nodes of the same harmonic series) but is there a state of the art that I should pay attention to? I’d like to avoid anything heavy to reduce ringing, if I take this route.