[Rodm1954]

Assuming timber or composite timber material would still be subject to humidity changes what then would make a good stable sandwitch material for a laminated plate?

[JerryBurks]

Assuming timber or composite timber material would still be subject to humidity changes what then would make a good stable sandwitch material for a laminated plate?

I think good quality plywood is just fine. I used Bamboo but Baltic Birch is almost as good and more available. While it is subject to humidity that can be controlled by proper coating and it is not a real issue when you start with properly dried stock. I believe the climate in Perth is not that wet, anyway. Actually wood has a serious advantage in terms of temperature coefficient which is lower than steel and way lower than aluminum.

Other options are high density PVC foam (expensive), box, or space frame design (look at Bartuss1's monster machine). Actually, if you use wood for a sandwich core it would be ideal to use end-grain sheet, that means where the grain is perpendicular to the sandwich surface like it is done for Balsa-core laminates. But that would be really difficult to get.

[Rodm1954]

Thanks for your suggestions.

Perth is normally dry but we do get humid weather. It is the extreme of long hot spells followed by a humid change that worried me. I have seen sheets of MDF bow is they face an open door.

[denz]

Steel

[cyclestart]

For strength/thickness of flat sheet it's steel, aluminum, wood in that order (obviously). For ease of cutting it's exact opposite unless the builder has the ability to cut the harder materials or the cash to pay someone else. A sturdy plywood router can cut aluminum sheet so a builder could bootstrap their way into a stronger build. Of course if there are no real gains from an aluminum/plywood sandwich this theory falls apart completely If nothing else it could be stronger at points of attachment (read: where things bolt together)

My gantry is 1.5" of plywood. The flex in the gantry comes from the points of attachment, not bending of the plywood itself. 100% guaranteed. When it comes to joining components the metal builder has a huge advantage.

[kostas1]

For strength/thickness of flat sheet it's steel, aluminum, wood in that order (obviously). For ease of cutting it's exact opposite unless the builder has the ability to cut the harder materials or the cash to pay someone else. A sturdy plywood router can cut aluminum sheet so a builder could bootstrap their way into a stronger build. Of course if there are no real gains from an aluminum/plywood sandwich this theory falls apart completely If nothing else it could be stronger at points of attachment (read: where things bolt together)

My gantry is 1.5" of plywood. The flex in the gantry comes from the points of attachment, not bending of the plywood itself. 100% guaranteed. When it comes to joining components the metal builder has a huge advantage.

So, I would say that I could use either 7mm steel for gantry sides or profile aluminium as showed in a very previous post, right?

[aarggh]

I've been trolled here previously as some people don't seem to believe the simple fact that others have mentioned, in that mass and size can play a lot in speed, forces, vibration and sound dampening. So in my opinion, the profile alu may possibly have an advantage depending on how you are fixing the asembly, in that it will physically be a larger section of material than the 7mm steel. Steel is strong but you also need to take the flexing of the materials into consideration. Gantry sides just made of 7mm steel will ideally need lateral reinforcing to completely stop sway or flexing, especially on rapids. Reinforced steel will be better than profile alu, but can you reasonably achieve that by welding or similar strong fixing methods? If not, then profile alu would be the easier way to go most likely.

Nice design by the way, I look forward to seeing the progress!

cheers,
Ian