Going to ask what could be a dumb question on one hand. But on the other possibly not. Anyway, I note some printers use wooden parts that appear to be structural, as opposed to just guards or cases. If this is correct, surely there is a stability risk and therefore accuracy/repeatability risk in these machines, especially when we are taking about accuracy/tolerances so incredibly small. Has this causes anyone any issues? Or is this not seen as an issue?
What about the fact that wood will expand and contract at different rates?
Fair point, well made. Thanks Brian
Not a stupid question. This was a topic of some discussion a week or two ago. The use of wood (plywood) is normally a pragmatic one: it’s cheap and can be easily machined or laser cut. All woods warp to some degree but it seems that with a stabilised plywood the movement is minimal; Ultimaker for instance use plywood and their bots have an excellent reputation for accuracy and reliability. In saying that Aluminium sheet and extrusions are also cheap and readily machined, less well suited to mass production for consumer machines perhaps as you can’t leverage laser cutting to production-line things. Personally I’d use metal over wood unless I’m prototyping.
Thanks Tim. Missed that discussion.
Given the print resolution of current printers, and what prints are being used for, it really doesn’t matter. We’re not building swiss watch movements from the parts.
So what about expansion rates on aluminium does that have a effect?
@Daniel_Joyce Not Sure if I entirely agree with that - a deviation of 100 microns in Z alignment is very noticable on high resolution prints and with people making good progress on small nozzle sizes and higher speed/higher accelaration printers, accuarcy and repeatability become more and more important.
So why use steel rods or wooden rod. Or any metal guides at all even metal bearings are going to move with expansion and as machines improve need products are needed.
I just asking as more printheads in the same size machines means more heat to dissipate and more will heat sink through rods and frames.
@Tim_Rastall I guess my def of high res is < 100 microns, or 4 thous of an inch. 
For my personal projects, I use printing services withe 0.001" or better resolution. 
So still not very ‘high res’.