Hi team! I am preparing some Skylark 200 blocks for the CNC and was wondering if the grain direction of the plywood matters. For longer pieces, they obviously can only fit in one direction. But for smaller pieces and bowties does it make a difference whether the grain runs vertically or horizontally?
I would imagine the plywood is slightly stronger in one direction but this would be negligible to any structural concerns - is that a reasonable assumption?
Thanks!
Hi @wilsonem,
the grain direction actually does matter for plywood.
Depending on which plywood you are using, the properties might be more or less different between the 2 directions. Normally, there are more plies oriented with he main grain direction parallel to the longer axis of the panel. Hence, in that direction plywood is stiffer and stronger.
As you said, for longer pieces the direction is constrained. For smaller panels, in principle I would try to nest (if possible) all the panels in the beam-column-joint with the direction parallel to the stronger axis. I attach a sketch if it helps. This might be less important for some plywood species or OSB, so maybe check with your structural engineer and the specific material that you are using.
Hope it helps.
Thanks @Gabriele - this is very helpful. I noticed the bowtie cutting files have the grain running the other way (WikiHouse) - not sure if this is intentional?
Hi @wilsonem,
we did notice that for the materials we have come across so far (OSB3,WISA,METSA Plywood) etc it would not particularly matter. The failure in the bow tie seems to be governed by shear rather than tension (more info here, starting from minute 12 .00 or so How to calculate a WikiHouse wall for lateral forces - YouTube)
However, if your plywood is for some reason significantly different across the two main directions, I would pay attention to the grain orientation. The bow tie might fail in tension rather than shear. It is worth double checking your structural engineering based on the actual material properties.
Hope that helps
