Veneering finished boxes with a vacuum press...crush risk?

[David Kuzdrall]

I am building some speakers with curved sides and am wondering about applying the veneer to the finished cabinet. The cabinets will be from laminated MDF (3/4" total thickness) and internally braced with 3/4" ply...but will this take the pressure of the atmosphere? The internal bracing will be significant...there will likely be some kind of brace every 50 square inches or so.


Has anyone done this successfully and / or has anyone crushed a cabinet? I am interested in the details of both outcomes.

thanks.

[richard poitras]

Use hide glue....

[john bateman]

I have done that on assembled boxes with less bracing than you have, and the boxes never collapsed.

There are other issues to contend with however. When veneering this way you must let the veneer extend beyond the edges of the box and trim it flush afterward. On a box with square sides you can just use a flat platen slightly oversized to press the veneer onto the substrate. But with a curved box, you will need a platen that can flex, meaning it needs to be thin. But this thin material must also be able to withstand the vaccum pressure without breaking where it extends beyond the edge of the box.

And of course the platen will be not curved until the bag squeezes it against your curved cabinet. So imagine trying to get all these things into the bag while keeping them all aligned correctly, with slippery glue complicating matters. Good luck!

[Steve Rozmiarek]

Good timing... I just tried to veneer a box of what I think are similar dimensions to yours. Mine was a curved front stand to raise a front load washing machine for my wife. I tried a dozen different bracing ideas, and I did not get a good result. I ended up painting it for now, but the issue was the vacuum is strong enough to deform the box around the braces. When the glue sets on the veneer, it sets the deformations into the curves, which makes a funny looking faceted surface. I was trying to skip a step and use the box as a form.

When I do actually get back to this project, probably never, I will just make a foam form and veneer a bending ply skin to apply to the box. This also fixes the issue John mentioned.

BTW, I tried hammer veneering this project too, and I still have had no luck with that approach on anything big. Just impossible to work a large surface quickly enough to get uniform adhesion. Paper backed veneer and contact cement would work better.

Steve

[Jamie Buxton]

I've done something related. I have a torsion box which I use as a really flat platen inside of a vacuum veneer press. It has 1/4" plywood skins, and a spacer grid that is about 6" on centers. Under full press pressure, you can just see the skin deflection between the grid members. I generally use the pump controller to back off the pressure. It doesn't take a ton per square foot to make veneer conform to the substrate while the glue dries; a pound per square foot works just as well.

However, to make your speaker boxes, I'd veneer the panels separately, and assemble them into a box. In the press, veneer and substrates squooge around, and glue squeezes out around the edges. The squeeze-out on later sides is certainly going to get all over the previously-veneered sides. When the bag tightens down on a big box with curved panels, it may slide veneers in directions you can't control.

Just as a side note, I always veneer panels over size, and trim them afterward. This deals with the squooging and squeeze-out issues.

[Jeff Duncan]

Also remember you don't need to "crush" the veneer you can turn down the amount of vacuum to get just enough to pull your veneer, but not enough to destroy your box;)

good luck,
JeffD

[David Kuzdrall]

Also remember you don't need to "crush" the veneer you can turn down the amount of vacuum to get just enough to pull your veneer, but not enough to destroy your box;)

good luck,
JeffD

What PSI range would be the minimum for most veneer glues?

THX

[Myk Rian]

The air will be drawn out of all areas of the boxes, so there won't be a crush potential.
Vacuum inside and out.

[Steve Rozmiarek]

The air will be drawn out of all areas of the boxes, so there won't be a crush potential.
Vacuum inside and out.

Only if the bag is inside and outside of the box. It won't be though, you'll end up with a wood box with air in it that wants to be a vacuum. Crushing is very possible.