Quote:
Originally Posted by Dad1279
Plane the wood to 1/2" thick, Drill lighting holes, and laminate one side with 1/4" hardwood plywood?
|
Don't waste your time or money on hardwood plywood. The face veneers may be very thin layers of hardwood, but the cores are crappy no-name softwoods. If you want the strongest plywood available your choices are marine fir AB, baltic birch 7- or 9-ply, meranti BS1088, or okoume BS1088. Okoume will be the lightest, the fir will have the worst QA problems, and the meranti will be the strongest. Good fir marine plywood would probably be the best overall, but I haven't seen a good, void-free piece in a long time.
There are woods that are very split resistance. Hard maple and a lot of tropical hardwoods have dense, interlocking grains that don't like to split. With natural lumber, I wouldn't use thin pieces, though. About 3/4" would be the thinnest you could go to without worrying about splitting. I might go with 4/4 (usually about 13/16" thick) or 5/4 (usually a little over an inch thick) and drill speed holes in non-critical points.
Plywood doesn't split, of course, but usually has the problem that 40-60% of the wood fibers run in a direction that doesn't help the strength of your application. A perimeter frame of natural lumber eliminates that 40% of the material running vertically which adds little or nothing to the strength of the frame.
Wood is nature's own laminate material: strong, stiff and light. It suffers when you run metal fasteners through it, and from impacts and abrasion. To avoid crushing wood fibers, you can bore a hole and insert a metal sleeve into the hole slightly shorter than the thickness of the wood. Run your bolts through the sleeves, put big washers on both sides, and tighten away.
In 2005 we pressed bearings into an oak bearing block and it worked fine. We captured the bearing in two blocks of 4/4 oak which were then screwed together. The beam was made of meranti plywood, and the bearing blocks were screwed and glued into the beam. The robot had some issues, but it was structurally bullet-proof.