DIY Gantry CNC Router - Y Axis - Moving Gantry vs Moving Work Bed

[Neale]

Briefly - moving-bed allows the gantry to be part of the structure of the machine, so stronger, and can be braced for more resistance to vibration. The moving bed can be pretty strong and well-supported. If you think about it, most milling machines (at least the traditional 3-axis sort) are effectively moving-bed. Big downside is that it has a much bigger footprint - over twice the cutting envelope along the bed axis.

Moving gantry has a much smaller footprint but needs care to make the gantry stiff, both to take cutting forces and avoid vibration/resonance, while being light enough to be able to accelerate and decelerate fast enough to give decent performance. What is decent performance, though? If you are cutting big rectangular panels, acceleration is nowhere near as important as for cutting lots of small fiddly shapes where cutter direction is continually changing.

So, this is an engineering problem and like most engineering problems, it's a compromise that has to take in what you what the machine to do (materials, cutting speeds, general fiddliness of shapes to be cut), material availability and cost (many people use aluminium extrusion but with welder and angle grinder steel is a practicable alternative), and your own skills and workshop facilities for building. There is no "one size fits all" solution which is why this forum is often asked for an "ideal machine" but you aren't going to find two people who agree on what "ideal" means!

Broadly, if the main use is a larger format machine for wood and plastic cutting, moving-gantry is fine. For steel, moving-bed. For aluminium, either will work but moving-gantry will need much more care in design and build and will never have the ability to cut as fast and deep as the moving-bed machine.

Best idea is to give a better description of what you want the machine to do, overall size, etc, look at examples in the build logs, and then propose an outline design that seems to match your personal criteria for constructive criticism.

Good luck - there's a lot of head-scratching and work ahead of you, but it's great when the machine is finished and working, and does what you expected it to do!