Epoxy granite or mineral casting

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Originally Posted by Washout

I've done some composite work and make the odd flight case for people using sheets of a carbon/kevlar/glass mix - the easiest way I have found of getting a glassy smooth finish is to use vacuum infusion onto a rigid sheet of perspex "mould" on a flat surface - you get glassy smooth finish with no bubbles.

Not sure, but you might be able to pull a thin infusion type resin through large sized grains of "rock" of some kind mixed with chopped fibres (I keep all my carbon/kevlar/glass off cuts for this purpose). If you can't vacuum through the aggregate, then pouring into a box mould with a perspex bottom should achieve good results. All the bubbles and crappy surface will be on the top and the shiny flat surface on the bottom, which you can then demould and flip over.

Heat would be my only concern, as large volumes which don't have a matrix of some kind tend to go off with cracks in them, but a few sheets of glass or carbon layered in the mixture should help solve that.

(Eyes up the gallon container of resin on the other side of the cave ;-) ).

Edit - nearly forgot - this link might hel with ratios Resin infusion; resin usage calculation

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My interest in the bases was piqued because of previous works with carbon gantry mills,there have been discussions for stiffer machines and carbon does the job nicely

My original question was to ascertain if anyone had done this granite thing in the UK
It seems getting on to a company that can answer the questions as they manufacture the machine bases cleared all this up nicely

To answer your question ..Yes!

This was for platorms at low level height in clean rooms for machinery to sit on. One thing we added was loose fibreglass to the granite resin mix. As far as a workable idea? the answer is yes and a good one.

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Originally Posted by JAZZCNC

Me too.!! . . . Yes please Sir.!! . . . (Would also mean Andy and I could play in the slap dab together. . lol)

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Mike looking forward to the info,looks like myself and Jazz could be playing in the slap dap after all :couple_inlove:

You may want to have a chat with these guys they make an entire lathe out of concrete, not just the footings or the base and they do attach the linear rails straight to the concrete. Aparrently they were used all the time in WWII (along with concrete ships) because all the metal was going into things that kill people.

MAKE | The Concrete Lathe Project

http://concretelathe.wikispaces.com/...esign+Drawings

Many years ago, long before the internet, and when I lived in warmer climes, I had the whacky idea of building an outdoors pool table out of concrete instead of slate but it ended up on the round tuit list.

Now this thread's got me thinking about the idea again....:abnormal:

INterestingly I was musing on the idea of a reinforced concrete z-axis support to replace the round column on my mill... one day in the distant future

By way of experiement I did the FEA on a 100x 100mm 5mm wall steel tube and a 100mm x 100mm concrete post, both 750mm high.

Ignoring any difficulties fixing the concrete post, the torsional stiffness wasnt so different. With an applied 200Nm twisting load 500mm out from the centre of the post :

Steel 0.34mm movement. Weight of column 34kg
Concrete 0.45mm movement, Weight 19kg. (thats with no reinforcement inside)

So with some refinement it certainly looks doable...

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Originally Posted by JAZZCNC

. . . Most of that thread is over complicated Bullshit.

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I agree with that 100%. My gut feeling says a bag of sand and a bag of gravel is all you need to make an incredibly strong machine base.

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Originally Posted by Ger21

I agree with that 100%. My gut feeling says a bag of sand and a bag of gravel is all you need to make an incredibly strong machine base.

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Someone agreeing with Jazz! That's a first!

If you want to talk to folks who work in some of the truly interesting end of Cement and ferrocement then you might want to look here Ferrocement Educational Network As they have been doing work with mesh re-enforced cement and other strangeness that makes some very interesting reading.

Michael

I do mineral casting Attachment 7655