I am working on the design of a bench-top CNC gantry milling machine. Yes, I am calling it "milling machine" because the intent is to build something that will be able to machine aluminum and steel, not just wood like CNC routers do.
I am currently considering various geometries. The most common out there seems to be what I think is known as the "moving gantry" geometry. You find these all over eBay and, of course, in real serious designs:
Moving gantry machine
The other design, less common in the little desktop mill world, is the "moving beam" approach. Here's a big boy that uses this design approach:
Moving beam machine
I am leaning towards going with a moving beam design using either thick welded steel tubular framing, epoxy granite or a hybrid. I have, BTW, read the vast majority of the huge epoxy granite thread.
Here are some of my reasons:
- You can have long work pieces extend out along the x and y directions
- Being that all active components would be on top of the machine, making a machine of a different height is as simple as replacing the frame
- With some creative design I can even think about the idea of having the ability to have huge Z axis space (not travel, just room). Think knee mill table lift married to a moving beam gantry.
- Inherently easy to deal with coolant and chips
- Easy to mount a nice sub-plate
- Sub-plate or machined-piece weight not an issue
- Can be enclosed (for chip and coolant control, maybe noise) very easily
- Less mass to accelerate along the Y axis
- Could be more rigid (highly design dependent)
- Easily adaptable to other configurations. For example, add a second bridge to have dual heads (crazy, but, hey, it's my list)
- If welded steel, easy to fill with epoxy granite for excellent damping
- Can extend frame vertically and have electronics right above machine
I am looking for feedback supporting either design configuration. I can see that in a moving beam mill whatever supports the ends of the beam needs to be design to be more rigid and deflect as little as possible under cutting forces. On a moving bridge machine this function is relegated to the machine's base, which could be quite stiff.
Thanks for your feedback.