[deprutser]

Hi All,

I would like to make an epoxy granite beam that holds a linear rail. I am planning to use this recipe, found here[1]
He speaks about 67% sand, 33% dust, 14% epoxy. In my mind this converts to 57.6% sand, 28.3% dust, 14% epoxy (all by weight). For the dust I'm planning to use this [2] aluminum oxide powder, and this [3] brand of epoxy

Now I know I can't machine epoxy containing sand and dust. So I want to create this cake:
Top layer: pure epoxy.
Base layer: epoxy granite.

To be able to drill and tap screws for the linear rails, I'm planning to embed vertical columns of rebar in the epoxy-granite layer, (flush with the boundary between the two layers) as this steel can be machined / tapped.

How thick must the layer of pure epoxy be to let it self-level into a smooth surface?
Is this the optimal way to do it?
Cheers,
Cedric

[1] https://youtu.be/gjw5juGG1g8?t=1062 Epoxy granite stiffness - test and results
[2] https://www.keramikos.nl/chemicalien...xide-1-kg.html
[3] https://giet-epoxy.nl/product/dikke-...poxy-giethars/

[joeavaerage]

Hi,
pure epoxy is 'squishy', without any fillers the expected Youngs modulus will be a s low as 4GPa. If you try to mount rails on it they will deform the epoxy for sure.

You need to have a solid steel rail or maybe aluminum cast into your epoxy granite and machine it flat afterwards.

Craig

[peteeng]

Hi Dep - The epoxy spec sheet says not to cast this below 1cm thick. This is because this sort or resin has very low activity hardener to prevent runaway exotherm and will not generate enough heat to cure in "thin film". 10mm thick will be very soft and unsuitable for rail foundations. If you use aluminium or steel powder for the top these are machinable and stiff. I imagine you are using the Al2O3 for its stiffness? You can use steel grit or fibres and this is machinable and cheaper then alox. Peter

The dome dark castings are alox - alox is black in this case. The domed grey castings are aluminium powder and epoxy and the LHS machined part uses epoxy and steel grit, it machined well even did threads. The RHS block is more steel grit reinforced epoxy. Shot blasters have a range of grits, metal, ceramic, plastic. Cheaper then chemical grade suppliers....Peter

If you can have the surfaces machined this is the optimal way to do it. I think self levelling epoxy although done is not a good approach. Either cast in metal inserts, or cavities for inserts then epoxy inserts in or cast the job in steel grit/epoxy then have it machined or have the mould surfaces machined so the cast is accurate...

The bottom blocks are UHPC/alox cheaper then epoxy and same stiffness but not machinable...

[deprutser]

Hi Dep - The epoxy spec sheet says not to cast this below 1cm thick. This is because this sort or resin has very low activity hardener to prevent runaway exotherm and will not generate enough heat to cure in "thin film". 10mm thick will be very soft and unsuitable for rail foundations. If you use aluminium or steel powder for the top these are machinable and stiff. I imagine you are using the Al2O3 for its stiffness? You can use steel grit or fibres and this is machinable and cheaper then alox. Peter

The dome dark castings are alox - alox is black in this case. The domed grey castings are aluminium powder and epoxy and the LHS machined part uses epoxy and steel grit, it machined well even did threads. The RHS block is more steel grit reinforced epoxy. Shot blasters have a range of grits, metal, ceramic, plastic. Cheaper then chemical grade suppliers....Peter

If you can have the surfaces machined this is the optimal way to do it. I think self levelling epoxy although done is not a good approach. Either cast in metal inserts, or cavities for inserts then epoxy inserts in or cast the job in steel grit/epoxy then have it machined or have the mould surfaces machined so the cast is accurate...

The bottom blocks are UHPC/alox cheaper then epoxy and same stiffness but not machinable...

I'm looking at iron powder. It can be bought with a grain size of 315um [1] or for a small premium, it can be bought with a grain size of 200um [2]. I guess the smallest grain size yield the stiffest and strongest result. Is this correct, or is a mixture of those 2 sizes more stiff?

Is there a danger of the iron and the metal of the rail interacting chemically with each other, creating rust and other problems? Is the metal powder safely encapsulated within the epoxy, even after machining?

[1] https://www.labshop.nl/ijzervijlsel-315-%ce%bc/
[2] https://www.labshop.nl/ijzerpoeder-gem-200-%ce%bc/

[peteeng]

Hi Dep - If you use iron or steel powder and machine it then I suggest you coat the surface with some epoxy to stop spot rusting. The steel/epoxy blocks I have cast and machined have not rusted but they are in my office not a workshop environment. A quick coat of epoxy will be beneficial. The UHPC/steel blocks I have made have surface rust on them and they too should have been coated in some way to prevent this. Peter