Thermal expansion of heated bed

The aluminium bed will expand when heated, and I will have to take that into account when designing the mount for my bed. But how much does it expand? I googled a number of thermal expansion calculators, and somewhat to my surprise they don’t give the same result, although they do give results in the same ballpark.

The calculator https://www.omnicalculator.com/physics/thermal-expansion seems well done and well documented. Using that, I get that a 300x300mm plate will expand 0.4mm in width when the temperature rises from 22 degree C to 80 degree C. The change in thickness is so small that it will not matter.

Another issue is that the bed may warp. Obviously a thinner bed will warp more easily, and as I understand it, a rolled aluminum sheet will warp more than a cast sheet. The very best is therefor a thick cast aluminum sheet.

I will have to take this into account when designing my bed mount. However, it also makes me think that it might not be so good an idea to print first layer(s) with a high bed temperature and later layers with a lower bed temperature - even a change in 10 degrees might mean a shift that will be visible in the object. I the shift happens over several layers it will of course be a lot less visible, I would think that 1-3 degrees change per layer probably is OK (but I have not (yet) tested any of this).

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