I’m about to start a gallery topic about improvements and modifications to my Shapeoko 3 XXL; I’ve found that my work has gravitated towards aluminum, and there’s some improvements I’d like to make.
In this process, I want to do meaningful research to help people achieve maximal “bang for the buck”, and to avoid modifications that have minimal impact or degrade the capabilities of the machine. So I’d like to keep things quantitative. Looking for some guidance and ideas.
Stiffness/rigidity/deflection: I’m intending to test as-is, then upgrade to an aluminum bed, and eventually move to linear rail for the Z carriage’s mount to the X axis. An HDZ is also a thought. Ballscrews down the line??
I purchased a fish scale and dial indicator, and would like to do some deflection quantification, at different locations on the bed. I’m thinking dead center and the SE portion, corresponding with the two areas I work in most (also, I have a pet theory that it’s stiffer in the corners). Is there a standard height above bed that people measure deflection at? Is there a standard endmill and protrusion from collet? Standard deflection force? If there’s not a standard, I’m inclined to measure half an inch above bed with a one inch protrusion from a 1/4" endmill (which?? or just solid shaft?), mirroring a lot of my work. 5 pounds (~20N?) looks like a common figure (is there a better number?) Maybe force generated at the cutter makes more sense?
Harmonic/Resonance suppression: I get a LOT of vibration from the machine. I also often get terrible surface finish on the edges of my parts. Are these related? I don’t know. I aim to fill the ways with either sand, shot, dynamat, or granite epoxy. I also intend to brace the bottom of my board and maybe dynamat it, as well.
I’d like to take baseline and modified figures, but I don’t quite know how to measure/quantify. Maybe set up a standard cut, and measure resonant frequency with something like a reed frequency meter? Maybe if I get an unbalanced motor and run monte carlo sweeps? (but then how do I measure resonance?) Which axes are the ones that matter? Maybe X and Y at the center of the table? Does Z matter?
Belt stretch: Sounds like steel core belts are where it’s at for aluminum. Is it because of belt stretch? I feel like I should measure the stock polyester belts under some elongation weight; maybe a week at room temp? Then see what happens at freezing and 100F? Or maybe just do some tracking accuracy tests with a drag bit over time.
Side question: Is there an optimal belt tension, in terms of force? We could use a torque wrench measurement to dial this in, instead of the ol “guitar string tight” guidance.
What other measurements should I be considering?