Quote Originally Posted by Christian Knuell View Post
Plywood is even worse than MDF because MDF at least does not warp and bend too much just because of temperature or humidity changes.
No sorry can't agree on this. Unsealed MDF changes shape if you so much as show it a cup of coffee let alone any decent amount of moisture. Ply wood will take much more moisture before swelling.

BUT to IMO both have only two places in CNC.? . . .Spoil board or to keep the workshop warm.!!

Steel is cheap and easier to work than people realise. Profile is fine but to get the best from it you need all the connection elements, T-nuts etc, and this makes it much more expensive. It's also harder to work than people realise, it's awkward drill/Tap and unless slots used then it can be difficult for mounting things too it with out adaptor plates.

Combination of steel and Profile works well IME, gives a good balance of strength and ease of build without getting silly expensive.