Hi All,



With a reasonable sized build the Rails are not to be worried about.

Why are you talking about “reasonable”? We’re talking about squeezing every last theoretical micron of accuracy and precision out of our builds!

I know, I’s kinda like trying to grind telescope optics out of Coke bottles with used playground sand, and insisting on a perfectly curved surface to work on… :slight_smile:


HAHAHAHA, I know…I never learn. I say it can’t/shouldn’t be done, then someone proves me wrong…or is that my plan all along?

Sounds like a PITA for very little gain.

If you want that type of accuracy… build your MPCNC and use it to cut all aluminum parts for a larger/more rigid structure.

Lots of folks commented on Tom S’s stream last night about filling the tubes. Seems to be a reasonable enough and common supposition. Hence the concrete sticky post. Foam seemed to be the most common suggestion.

I am curious if foam in the side rails would decrease any resonance and cut down on noise. Having side rails that are 36", I have more room for issues. Put mid-span supports in and everything is smoother. Also getting my bearing hardware tweaked just right to ensure contact. I’ve had a few bearings that weren’t contacting 100% and that gave some buzzing.


A normal 24" bed it seems to not be an issue. Only when folks push the envelope do you get into complications.

Everything I have read here on from the many posts on YouTube and other places is that the MPCNC is a great design as is. Follow the specs. It just works. And I am a believer. No tweaking in software needed having bought the Archim 2 board and the steppers from the shop.

Epoxy granite has similar/better resonance dampening properties than cast iron. I am kind of tempted to build a smaller machine with stainless rails, filled with epoxy granite, specifically for milling aluminum. Just go overboard on anything that could possibly add rigidity, then use it to cut out the plates for my from-scratch CNC mill design.

Especially since I’m upgrading my minirambo so I’ll have an extra minirambo laying around…

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I would love to see the equations for that but I am sure a few milimeters shorter tube would far outweigh any filling you could possibly put in a SS tube. Even more so for a Shorter Z axis and legs. So if you really wanted to beef it up mount the bottom corners directly to a table and skip the legs/locks/feet. A few build them this way.

I’m not a Mechanical Engineer and my ME friends don’t like me enough to do math for me.

But I could do a before/after test.

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Like I said, I am wrong all the time, I am getting curious if I was wrong about this. But… I am confident enough not to spend anymore time on it myself.

I find that hard to believe. You must have really pissed them off somewhere along the line if they’re not willing to do maths for you. Not willing to show you the maths, or give you the proofs… That I can understand. That would require payment or romantic entanglements.


I was at work one day and an Engineer put an quadratic problem on the whiteboard. He was looking at it for a while, a little too long, so I got up and started asking questions. Then the other engineer got in, and a few minute later the boss (also engineer) got in on it.

We turned around and all of the designers were cracking up, Just watching us having fun doing math. HAHAHAHAH


It’d probably be easier to fill the tubes with sand and cap them than it would to try to pressurize them. Plus side to the sand is then you wouldn’t be running a small pipe bomb in your basement.

Yea, I’ve seen the point loads put flats on stainless, pressurized stainless would be awesome to watch, over a camera feed.