If a bracket is not sturdy enough at one size, you use a larger size, right?
@NathanielStenzel yep. Just keep in mind that a small aluminum bracket is much, much stiffer than a large plastic bracket.
I forget the exact recommendation I put in my book, but for aluminum the bracket length of engagement on the extrusion should be ~5-10% of the length of the extrusion for maximal stiffness.
@Ryan_Carlyle I get the idea that properly sealed wood is better than plastic by 50% or better. I think it being sealed will help reduce the chance of heat triggered warping. I think that sheet metal on the side of plastic or wood will put it about half way between the plastic/wood and a pure metal bracket. Of course for a small wood/plastic bracket is still a bit lame, so you still want to scale up a little. What do you think?
@NathanielStenzel do you mean actual wood, or engineered wood product like plywood or MDF?
All wood will change dimensions as it absorbs moisture or dries due to changing humidity. So thorough sealing all surfaces is critical. This won’t make it immune to dimension changes, but it should be “stable enough.”
Actual wood is highly anisotropic. Depending on the grain orientation, it will have different properties and different expansion/warping with environmental changes. For example, if the grain isn’t straight through the board, it’ll slowly warp as humidity changes.
MDF and melamine type particle products will swell and warp, and also creep under load. (Got any cheap IKEA shelves sagging under weight?) The edges are “thirsty” and tend to absorb sealant so you need multiple coats. I don’t recommend.
OSB is pretty stable. Plywood is ok if it has a lot of layers (i.e. thicker is better).
In any case, good frame design can help overcome warping… EG building T-beams and closed box frames will allow the strong axes each board to constrain each other. Basically wood frame construction is a specialized discipline that requires different design approaches to work with enough precision for printers.
@Ryan_Carlyle mainly pressure treated and then sealed wood would be the best choice for me. MDF too maybe.
@NathanielStenzel dunno if I’d want to use pressure treated wood for a printer. It needs a fair amount of time to dry out before you can seal it. Plus it’s kind of toxic (not as bad as it used to be, but not good for you). Melamine/MDF with the edges sealed would be fine.
@Ryan_Carlyle huh…okay.
Ordered my 2020 x 500mm extrusions from Misumi. Passed on the corner cubes. Passed on the corner braces with poor mechanical advantage. Going to try 3D-printed corners, though I am skeptical about plastic.
My speculation is that plastic corners with metal diagonals dividing the stress … the plastic corners might be sufficient.
Divide and iterate…