Deflection calculation

Mostly Printed CNC - MPCNC Troubleshooting
1

So I’ve taken the plunge and ordered 1" 304 steel for my ~6x3 ft cutting area build (84" and 48" tube lengths). I realize this is something I should have done before ordering parts, but I’m trying to figure out the deflection of the cross beams to make a rough guess at what kind of real-world rigidity I can expect. For the sake of argument assume that I’m going to fully support the frame, so I need only worry about the gantry. I’m assuming the most deflection I can expect would be the full weight of the tool head supported by the shortest cross member (48")…

I guess I have two questions: 1.) is this a reasonable worst-case assumption, and 2.) how much force would typically be applied by the tool head?

A third (and only somewhat related) question: Could I add a “sliding” support cross section that would allow me to support the gantry for smaller pieces, thus preventing me from having to maintain 2 machines? Has anyone tried this?

2

The math is so far above my FEA skills I would have no trust in the final calculations. I can’t help you here.

Flex of the rails, flex of the plastic (numbers would be very different for each printer and plastic infill and density, ambient temp ect), flex of the mount, slop in the chuck, flex of the bit (different for each material and tooth load).

3

Fair enough. I was mostly just trying to think of a scenario that I could use as a reference point lower that the bounds of the machine so I don’t get my hopes up too high :slight_smile:

I got my tubes in yesterday… Looking at how thick the steel really is, I’m sure it’ll be fine for wood. And if not, I’ll cut it down and use the spares to make a tiny second one for aluminum milling.