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How to make these without warping11/15
I have to make a dozen or so of these that go into a house on the harbor.
They are alder ply (pro core and veneer core) going to be stained and lacquered at the job.
I was thinking maybe they should be sealed on the inside before assembly.
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The dimensions are 156" tall and about 30 wide by 2" at the face
Assuming that the nosing is a piece of solid, as long as the solid is milled flat and true, you should be fine. To quote David, "Build flat, stay flat." I would certainly agree that finishing the inside won't hurt, could help. I would make sure they get assembled soon after finishing the inside though so it doesn't sit unbalanced for long. Otherwise, the only thing I can think of is to make it a torsion box with 1/4" veneered skins.
I don't know how much weight is saved by having strips between the two outer skins, but if you put solid material as the core and it was glued flat, there is a good chance that it would stay flat, as it would be a balanced construction with no place for environmental factors to manifest themselves against the inner face of the skins.
You could use some light weight material for the core, such as honeycomb, and groove the top, bottom, and back of the column to provide attachment to slide onto onsite blocking.
Some might argue that it is already balanced with strips as shown, and whatever happens to one side would happen to the other, with perhaps only the possibility of cupping the faces of the columns because of unbalanced finish application.
Finishing the inside first, and waiting who knows how long before the outside is finished, is asking for trouble. My two cents, I am sure others will disagree.
Hope this helps.
If the ply panel faces are 3" thick, then you only add 1/2" strips to the interior. Space them apart about 3" or so, and you will be fine.
Your imbalance is balanced. The finish is balanced on the whole panel.
You could go to 1/2" panels and a 1" filler, and still be balanced. At 1/4" panel faces, I would then go to an egg crate of a sort, and a full on torsion box.
Use a more rigid glue rather than a less rigid (TB2 or TB3).
And "Build flat, stay flat" is wise. Make a solid structure that these can 'pile' onto as they are assembled. Be sure it is very flat, and all panels are oriented the same way.
Design-wise, I hope these are far enough apart that one can't sight one against the other, or slight differences in 'flat' may be apparent. At 2" thick and 13' tall, they could act like a piece of paper stood on end.
Use 3/4 x 2 solid jointed straight for the nose. The nosing and the fixing to the wall will keep it straight.
We typically use a bit of glue and a cabinet stapler for the blocking. Be careful to lay the big panel down on a flat table. Clamp the whole thing to the flat table not saw horses when putting the 2nd piece of ply down. Otherwise you will induce a bow.
If you REALLY want to go over the top....
It won't move
Thanks for the input, very useful
Karl is that lattice necessary for a torsion box?
Sorta. It was basically a subframe for a stainless countertop a buddy was making. It was supported all the way, so it was more just for filler. It probably didn't need to be at an angle, but the steel was going to be longer than we had material for, so making it like that was an easy way to make it longer than that material available. I was also screwing around a bit. When you're not making any money anyways, might as well experiment.
It wasn't super stiff on it's own, but sheeted and properly adhered, I'd bet it would be bonkers stiff.
For what you're doing, I'd just run some dados to index placement of the strips like David said. For me, I'd probably glue them up a little oversized, then trim them to size on the panel saw just to make sure the two edges are perfectly planing out. My panel saw only has a cutting depth of 2¼ though, so if thicker than that, I'd have to re think my approach. Then just apply the face edging.
Or.... I don't have enough length on my cnc, and you wouldn't get that out of a 5x12 anyways, but a big miter fold like that looks pretty sweet and seamless.
I'm not sure that these the filler strips at all
These are going to be screwed between cabinets in spots
these the filler strips at all = the filler strips are needed at all