[walter]

Larry, we may be onto something here

Our home made machines are growing in size, it takes ridiculous amount of time to weld these silly structures...

The alternative should be:

1. pourable, non toxic
2. low cost
3. zero shrinkage
4. self leveling
5. low cost...

The idea is to use concrete-like solution for frames, tables, etc.
How thick can we go with this "polymer-concrete" type of products?

Do we need reinforcements?

I'd like to be able to "pour" my frame- let's say 2"x4" slabs of zero shrinkage concrete-type-of-stuff. I would just use regular Home Depot cement but that stuff shrinks..

I think the self leveling feature is also important- imagine router tables with 8' - 16' of work area... Such a pain to level those linear rails!

My solution- just pour a 4" x 4" slabs and fasten the rails.

Yes, some of these compounds have incredible properties (vs cast iron) but we're trying to solve some very "basic" problems here.

[greybeard]

For the "larger" size tables, would there be a good case forbuilding it straight onto the floor ?
You may well need a fence around it to keep the kids and the pets from investigating this noisy "animal" tearing up and down, but if you've already got a concrete floor flex in the x axis shouldn't be a problem.

You could even park the car over it ?

John

[dansutula]

Folks,
The former Light Machines Corp. (Manchester, NH, USA), now owned by Intelitek, has been using Polymer Concrete for the frames of their top-line ProLight PLM and Benchman milling machines for nearly 20 years now. At one time (in the mid 1990's the bases were being made by ITW Philadelphia Castings. In fact there were pictures of the PLM molds and castings in the ITW catalog. I'm not sure if ITW is still making the bases for Intelitek, and I suspect possibly not, as I have noticed some minor changes in the newer PLM castings, and an absence of the PLM pictures on the current ITW website (although this may be for "trade-secrecy" reasons).

At one time I had seen an intentionally fractured sample bar (2"x2"-ish tensile or flexure test?) of the "zanite" type material used in the PLM bases. As I recall, some of the quartz or granite aggregate was similar in size and shape to "fish tank gravel" like BB-size (.18-.25" / 5-6mm). Anyhow - when professionally engineered/applied, polymer concrete can be an outstanding material. And with a bit of research and experimentation, I'll bet that us DIY folks could yield very good results. Good Luck!

[Mcgyver]

Larry, we may be onto something here

Our home made machines are growing in size, it takes ridiculous amount of time to weld these silly structures...

I had never thought of an epoxy granite structure as replacing a steel fabrication, its not strong enough imo, the yield stress is much lower than steel or cast iron irrc and the modulus of elasticity is about 1/6. saw it more as a way to stop a fabrication ringing like a bell. commercial practice suggests the same, where I have been able to see commercial uses for epoxy concrete, it is either filling the voids in a CI or steel structure OR use as a heavy base for machines deploying negligible forces, ie optical equipment. I would not make a metal working machine just of epoxy concrete, not unless a lot engineering calcs proved my assessment wrong. don't forget to normalize any fabrications going into a machine

Larry, we may be onto something here
Yes, some of these compounds have incredible properties (vs cast iron) but we're trying to solve some very "basic" problems here.

Larry you mentioned earlier 50X better than steel and 10x better than CI for epoxy/granite's vibration dampening abilities, seems high to me. I'd read CI is 1x better than steel and Epoxy granite 50% better than CI. Not that easy to find info on the subject though, after all vibration is a magnitude and a decay, its not straightforward, at least to me, what better means, but 10x seems high.

thanks for all the good info being posted on the subject, I continue to believe it holds promise for high end diy machines

[Geof]

...Larry you mentioned earlier 50X better than steel and 10x better than CI for epoxy/granite's vibration dampening abilities, seems high to me. I'd read CI is 1x better than steel and Epoxy granite 50% better than CI. Not that easy to find info on the subject though, after all vibration is a magnitude and a decay, its not straightforward, at least to me, what better means, but 10x seems high.

thanks for all the good info being posted on the subject, I continue to believe it holds promise for high end diy machines

This page has the numbers claiming better damping characteristics:

http://www.accurescasting.com/polymer.html

On other pages I found some rather unbelievable claims for casting accuracy such as +/-0.0005".

But they do refer to 'machine bases and support structures' so they are not talking about using this stuff for the entire machine.

[turmite]

Then I guess this machine won't work!

Here is the story link.

http://www.machinedesign.com/Content...MecRG02-01.jpg

Mike

[lgalla]

Walter
Epoxy is only nontoxic after full cure, one week.People tend to think it is not toxic as it has no flamable solvents.Epoxy can pass through your skin.Wear gloves and mask if sanding.
Larry

[Geof]

I found this page which gives a lot of answers that lead me to conclude this is not a technique that can be readily adapted to DIY; considering you first need to make a very precise steel mold and the material cannot be worked after casting.

http://www.itwpolymercastings.com/faqzanite.html


But the materials are not difficult to find:

"Zanite® polymer composite is a blend of pure silicon dioxide ceramic (99.8%) quartz aggregate, specially formulated high strength epoxy resin and selected additives. The natural elliptical shape of quartz is ideal for casting intricate structures."

In fewer words; sand and epoxy.

[walter]

I had never thought of an epoxy granite structure as replacing a steel fabrication, its not strong enough imo, the yield stress is much lower than steel or cast iron irrc and the modulus of elasticity is about 1/6....

Good point.

Then again, folks here don't build metal working CNCs. 90% of these machines are destined for wood, mdf, foam, plastics, aluminium.

I'm into wood machining, and really dislike the idea of steel tubing, welds, drilling. Fastening together 800 lbs of tubing would take months! I even hate the smell of it

I just need the basic rigidity and level- I'll go with (reinforced) concrete type of material.

Thanks for all the replys- you guys are the best!

[Mcgyver]

Good point.

Then again, folks here don't build metal working CNCs. 90% of these machines are destined for wood, mdf, foam, plastics, aluminium.

thats part of it - different paradigm - no doubt we're visualizing two very different machines! its building metal working cnc's that interest me, I have little interest in wood machines for now. my thoughts were that a heavy weldment, using structural shapes could be filled with E/G and you'd have a chance at a metal working machine, small work envelope but very heavy and rigid. still, from I've been able to learn, its advantage over steel/CI is in vibration dampening, not strength or rigidity.