[immutef]

So what your saying is it's better too insert aluminium bars and have them milled for the linear rails than use steel. Just about to purchase supplies for mine

No, its not "better" because Kern does it. Kern uses aluminium because its easier to cool, so thermal expansion is less of an issue in their machines. The actively cool the aluminium, which is probably not doable for a DIY machine. For hobby/home/semi-professional use, steel is the better choice, since material properties are more similar to epoxy granite than aluminium.

[vakeiros]

No, its not "better" because Kern does it. Kern uses aluminium because its easier to cool, so thermal expansion is less of an issue in their machines. The actively cool the aluminium, which is probably not doable for a DIY machine. For hobby/home/semi-professional use, steel is the better choice, since material properties are more similar to epoxy granite than aluminium.

exactly.

however I don't even consider it a problem, I mean the amount of expansion I don't think it to be relevant at all, if it was an abrupt and wide temperature difference it might but in our case it's a low difference over long time and due to the aluminum great thermal condutivity I don't think it will really matter... maybe it does if you're chasing microns otherwise it's just kind of irrelevant I believe... for me I just use what I can get easier...