Machine bed material

[iskender]

I'm planning to do a machine with similar design, but with concrete instead of epoxy. For the machine bed, a pre-milled plate will be layed on top of the concrete and bolts will hold it inside the concrete. I'm choosing pre-milled because I don't have any spare cnc to mill it afterwards and also not interested in scraping it. My question is what "therminal expansion" is reffered to here? Is it possible for the plate to be distorted AFTER it is layed in on top of the concrete? And i'm not asking about any distortion due to use, or environmental factors, i'm asking just about the process of laying it on top. I know concrete heats up while stiffening, but is that going to distort a 2cm thick steel plate? And if yes, i also don't care it distorts it it 1 measly micrometer or something like that. So what thermal expansion is reffered to here?

[Aust12]

Hi all. I finally built the mill. I used 20X75mm plate aluminium for the rail bases. When I added the epoxy the rail bases shifted slightly. It worked out ok it’s accurate to 30 microns or less. I was thinking of doing a redesign to try and improve on the accuracy. I have attached the drawings of what I’m planning. It will be made out of 50mm thick c45 steel the base will measure 500X400mm. There should be a nice but if weight in it.
I know it’s preferable to make machine bases out of cast iron but would C45 hot rolled steel work for this machine. The surfaces for the rails will be ground flat. It will only be cutting brass aluminium and sometimes small bits of steel.

[John McNamara]

Instead of on top cast the steel within the mineral casting (Epoxy granite to some)

https://www.model-engineer.co.uk/for....asp?th=139042

There will be very little heating assuming you are using slow cure epoxy at around 15% of the mix.