Gents,

first of all, if this is in the wrong section, please feel free to move the thread where it should be.

I know this questions must have been asked numerous times, although I couldn't find to many threads about this on this board. I'm in the middle of prototyping a CNC related machine and the initial idea was to use 18mm MDF as it's flat and cuts rather easily. Recently someone suggested HDPE, and later on ply was suggested, as a natural alternative to MDF. I've looked at HDPE and it looks solid and stiff, although it's not great when it comes to thickness, suppliers can guarantee 18mm +/-2mm. Ply seems to be more stiff and rigid than MDF (which is basically glue and dust), but warping is a problem apparently, although MDF might suffer from it as well.

So out of the three, can anyone suggest one that's better than the others? I'm currently planning to use 18mm MDF, using cross dowels to hold the thing together. The forces acting on the machine are minimal, it's mostly about precise alignment of all the parts, there's two bearings which will be pushed into the MDF (holes 0.1mm smaller than bearing dia) and a z-axis like gantry on linear bearings. Final model will be made out of ali, so this is mostly for dimensions checks and overall idea testing, although it needs to be stiff and precise.

Cheers,
dsc.