Veneer on plywood - how thick can it be?

[woodbe]

Hi.

I'm building a computer hutch for one of my kids for christmas, and I'm going to use some timber I experimented with for the top. (It's maybe lacewood and meranti according to , joined on a wavy curve using the bandsaw)

Anyway, once I hatched this plan, I started thinking that the thicknessed result (about 12mm) was probably going to be a bit risky from a strength and stability point of view, so I'm thinking of building the top from 16mm ply and attaching the curvy top to that with a meranti border to cover the ply and edge. I'll cut a stopped trench and use some meranti panels for the legs. Dimensions will be about 900 wide x 300 deep

So the question is, how thick can I leave the board, and how should I attach it to the ply? Could I apply glue over the whole length and width of the board and clamp it, and will it behave over time that way? Or should I do something that allows the top to move relative to the ply?

Happy to post pics of the board when I get a chance, it's turned out rather well if I do say so myself :)

woodbe.

[Pusser]

I stand to be corrected but the 16mm top will move because it is solid timber. The plies in the plywood do not move as they are too thin and the glue locks them all together. You will also have warping problems as the upper veneer is now 16mm thick and will not be balanced by the bottom ply so moisture will effect one more than the other.

I would have thougt 16 mm was strong enough. if in doubt you could put a couple of reinforcing cleats underneath. You can put an edging on if you want a more "robust" appearance.

[woodbe]

Thanks Pusser,

The timber is 12mm thick, not 16. It's the ply that is 16.

I can thickness the timber down to maybe 3-4mm, don't know if that's thin enough to avoid the problems you speak of though.

The other alternative is to attach the timber to the ply using some sort of loose attachment method that will allow it to move.

woodbe.

[woodbe]

Ok, I've thought about this now. The issue is that the timber will be too thin to give full strength, and it's expansion/shrinkage over time might tear the top to pieces.

So, my plan is to not glue the timber into the top, but capture it in a rebate as per the picture. My reference book says that the maximum variation is about 14%, so over 300mm (the cross-grain dimension) I should allow about 4mm or 2mm per side, and drop a single spot of glue in the middle to stop it wandering about.

Will that work?

woodbe.

[m2c1Iw]

Woodbe, not sure of your design but IMHO drop the ply and use heavier edging for support of the panel or perhaps torsion box style using 12mm mdf for one side hope it makes sense.
Cheers Mike

[Brown Dog]

I dont see why it would'nt.....as long as your happy with a gap all the way round the top. I might also be inclined to intall some cleats underneath the top to make sure it stays flat.

personally I would resaw the timber into 2-3mm thicknees and veneer both sides...though this could be a fair amount of extra work....your solution would be easier

good luck
BD:2tsup:

[woodbe]

Good point. It's going to collect grunge and pencil leads etc.

How about this then?

[woodbe]

Resaw is out of the question, I can only go to about 200mm...

[Brown Dog]

I think that would work...you have allowed for expansion in the timber. Again I think you would need to add cleats to the underneath just to ensure that any cupping is contained. I would be worried about this because one side of the timber top is exposed and one side is covered....Im only guessing but that could lead to a differential in moisture loss and maybe cause the top to cup.


Resaw is out of the question, I can only go to about 200mm...

Why would resawing be out, if you can cut 200mm deep...your top is only 300mm?... All you would need is 4 strips 150mm wide 3mm thick by however long. Edge glue 2 strips together then glue to top and bottom of you substrate... if you get what I mean

cheers
BD:2tsup:

[woodbe]

Hmm. I'm going to think on this. The board is already assembled, which is why I cannot resaw it. Might be another way, like m2c1Iw (http://www.woodworkforums.ubeaut.com.au/member.php?u=15400)suggests or something...

Thanks for your help.

woodbe.

[Pusser]

Plan B would work. You could seal both sides of the timber with finish and both sides of the ply. A coat of sanding sealer over the ply would probably do it. A couple of cleats accross the ply might be the irish solution (to be sure to be sure).

[Wizened of Oz]

Hi.

So the question is, how thick can I leave the board, and how should I attach it to the ply? Could I apply glue over the whole length and width of the board and clamp it, and will it behave over time that way? Or should I do something that allows the top to move relative to the ply?

woodbe.

At a workshop I did with Richard from Rivergum Timbers (veneer supplier) his rule of thumb was up to 2.5mm behaves as part of the substrate, over 4mm behaves as solid timber.

[woodbe]

Hi.

A liitle progress today.

Thicknessed down the panel some.

Jointed it on the router table using a straight bit and the offset fence trick. (Works well)

Cut, thicknessed and jointed another board to make up the width, glued and clamped it.

Still thinking about the other business...

woodbe.