MK2: moving gantry router for metal cutting - comments sought!

[paulus.v]

Thank you all for your input!

I'm intending to add a layer of foil-faced Tecsound damping sheet inside my gantry extrusion, I've found it very effective in the past on metal enclosures. I may also try some expanding polyurethane foam, either on it's own or in conjunction with the Tecsound: just need a bit of time to experiment!.

Tecsound looks promising. Not sure how different could be compared with the ISODAMP C-1002 mentioned in the MIT paper. A friend is soundproofing cars for 'dB drag racing' with StP. Not sure how good it is at vibration damping but I'll test it.
I don't think the PU foam has any damping characteristics. If you knock it the sound is very well propagated.

The answer is easy, the implementation of it is not, you set up a factory to make the Aluminium Foam filled parts of your choice, it is not an "Aftermarket Filler" choice.

I see a few books cited on wiki about ally foam manufacturing. I need to get my hands on one of these books.
Here's an experiment but the result doesn't look that great. https://www.youtube.com/watch?v=8FHTK2LZNTY

In the end, for this size of machine, the weight vs dynamics can be managed with appropriate motion component choices.

Exactly here's my problem. I need a lightweight machine, and being light allows me to use steppers and the price difference to servo I can use to improve damping and stiffness without adding to much weight.

Wow, never heard of this! Veeeery interesting. You just added another option to investigate to my list.

About shrinking/retraction, I don't think this such an issue, or at least that it can't be solved easily, as this is a construction method used daily in buildings. Quite sure there should be something in Sika or other product range for this problem.

This is actually my champion ATM! I find this Constrained Layer Damping technique very interesting by its use of multiple materials, smart mechanical principle, and affordable materials and build techniques.
Visco-elastic mat used in the thesis can be found and is not insanely expensive, and I'm sure can (and most probably will) be replaced by other cheaper and/or more easily available products. I'm currently thinking to asphalt mats...
They also use (IIRC) aluminum oxyde in concrete mix as an expansion agent, which should also be an answer to the previous retraction issue.

I doubt the expansion agent will work with foam concrete as it will tend to put pressure on the air bubbles in the concrete not against the walls of the mold. This chart shows that the shrinkage increases as concrete density lowers.

Even if I'm a little surprised by your stiffness numbers... Price remains one of the top decision factors, at least because all cents saved in structure will be to increase quality and performance of other components.

i have checked the deflection only with online calculators, two for each and they gave similar values. But now I tried a lot more calculators fot the RHS and the values were different... from 0.007 to 0.11

Could any engineer here help me with a proper calculation?

Other usual suspects are epoxy concrete/granite casting, and of course, solid granite stone. These are my second and third options.
You'll find tons to read about the first, and high end machines are also built this way.
About the second, you should be very interested by this build series https://www.youtube.com/playlist?lis...BoMfvQ8Ttsq-57 (as well as by all other videos from this guy!)

Interesting granite build.
The epoxy-granite is another story. There's the famous thread on cnczone with almost 5000 replies. But as far as I understand it, the most difficult part is the vibration for compacting. Vibrators are not cheap and not that easy to build and for good results they need to be tuned to the right frequency using inverters...

But a epoxy-granite cnc wouldn't be lightweight so it is out of the question for this build.

I won't even look for pricing infos just to not feel the pain!

They say 5-6 times the price of roller rails. But the price of their rails not the hiwin ones... And requires a dedicated oil pump.

Hi Paul,

Are you sure about the stiffness you describe above.

As a rule of thump, steel is more rigid by a factor of 3 for a given shape at the same weight.

Box section should be more rigid than tslot profile..

You explain above the tslot alu 13.5kg is more rigid than the steel box at 18kg....

I am not saying you are wrong... it just doesn't sound right.
Please check to make sure.

Also weight is your friend preventing vibrations.

I know it is hard to make the choices.

If you have access to tools and skill to go the steel frame / epoxy route i recommend it.

Grtz Bert.

I'm not sure anymore about the hollow section stiffness... If the calculation was wrong and stiffness is not a problem I'll probably take the steel/epoxy route with some sort of vibration damping inside them.