Epoxy-Granite machine bases (was Polymer concrete frame?)

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Originally Posted by 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...

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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

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Originally Posted by walter

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. :)

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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

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Originally Posted by Mcgyver

...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

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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.

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

Then I guess this machine won't work!:)

Here is the story link.

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

Mike

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

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.

Mcgyver and Geof
I have to agree, I cant see a hobyist building an entire machine ofE/G.For us hobbists we can use it for table tops,machine bases and weldment filling.Yes there are commercial machines totally composites, made in molds.
I would hate to think what would happen if a forklift bumped into a 100% polymer machine
Larry

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Originally Posted by lgalla

...I would hate to think what would happen if a forklift bumped into a 100% polymer machine Larry

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I would hate to think what would happen if a forklift bumped into any machine!!(chair)

But I do have a question: You say; "there are commercial machines totally composites", are there really? All I have read refers to machine bases not the full machine.

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Originally Posted by Mcgyver

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....

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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! :)

Mike - could you revise the link to that story in #23 as your link is only to the picture.Thanks
John

http://5128.rapidforum.com/topic=110...6&search=beton

try this link. German cnc site. Just look at those pic's. Looks Good

schrupphobel72 - Your last three images are corelpaint (?) could you make them jpegs so we can enlarge them.
Not sure about the link as I don't read German -it's a forum, I think ?
John

And now for the bad news, cost.
Lets assume$50/gal for epoxy,10 cents a pound for sand.I will round off to the nearist numbers.
To simplify things we will try 33 1/3 % epoxy/sand.
1cu/ft epoxy=7gallons =70lbs=$350
1cu/ft sand=166lbs=$16.60X2=$33.20
Now we take 1 cuft epoxy and 2cuft sand and have our33%to66% ratio
So the cost for 3cuft=$350.00+33.20=$383.20
Cost per cuft.=$120.00
Weight of 3cuft 402lbs
Cost/sqft=$10.00
Our 3cuft at $383.20 gives us 32sqft one inch thick.
Looking back to post #10 from Episs we are close to the same price and weight
More calculations for my 6'X12'X4" router table.Lets see 72sqft4"thick=280sq ft X$10=$2800.00 Total weight 3080lbs
Larry

Larry - Why not use a layer of patio paving slabs as the top, epoxied together, then coat that with 1/4"skin(or even less?)
John

Build a torsion box out of paving slabs ?
John

attached the pic's from the german site again

Attachment 29436


Attachment 29437

Attachment 29438

Attachment 29439

Attachment 29440

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Originally Posted by walter

Good point.

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

:)

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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.

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Originally Posted by greybeard

Mike - could you revise the link to that story in #23 as your link is only to the picture.Thanks
John

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http://www.machinedesign.com/ASP/vie...MDSite&catId=0

Sorry about that.

Mike

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

I guess my first post wasn't clear enough. The only thing on the structure of this machine that is metal is the bed. Go read the info about it. It is a metal working machine made almost entirely of the PC you have been discussing here.

If you search you will find many articles about metal working machines that have been made that hold better tolerences because they are built of PC.

Mike

That is the link that claims a casting precision which I find hard to believe. Here is a quote:

"A mixture of reactive, high-strength resin and mineral aggregates makes as-cast machine components to 0.0005-in./ft flatness, with hole diameters to ±0.0001 in., and feature dimensions to ±0.0005 in./ft."

At my last job we did some experiments with replicated surfaces using epoxy based materials. What we found was that we were able to produce replicated surfaces, using a large granite surface plate, with a flatness within .001" over about 3'. The biggest problem we had was the hardness of the surface. We were running an air bearing over the surface. If any grit got on it tended to get stuck in the epoxy and could end up scratching the way or worse the bearing.