Please help - having difficulty making Ply that don't curl

[nick1982]

Hi,

I'm making A4 sheets of 5ply wood.

I'm sandwiching American walnut between ash, so when I bevel the edges there is a black band through the middle.

the 1st one I made, I used PVA wood glue. I used two sheets of ash, then two sheets of walnut - I cross grained, glued both sides and pressed - It came out flat. then it bowed. wet the wood and pressed it again, it went flat, it dried. I took it out.. and it bowed.

My second experiment was to use an extra sheet of ash, and this time cascamite. I had 5ply, which is now a little thick for purpose. I let it set for 24 hours in the press. I took it out. it was flat. Then over the next few days it curled, not as much as the last but enough to make it unusable.

Does anybody have any suggestions to help?

I've thought about using veneer softener before pressing, the veneers were in long strips an wound up for transport. I thought pressing with glue would be the same thing as using a softener and pressing.

I also thought maybe I needed to leave it in the press longer with the cascamite? My theory being that as cascamite is resin that if it is pressed until fully cured it'll prevent curling.

My second theory is that I need another wood? I thought as and wallnut would be ok though dues tho there grain pattern.

Any help much appreciated.

Thanks,

Nick

 

[NazNomad]

Can you not orientate the grain directions, like actual plywood?

 

[AJB Temple]

When you buy veneers that have been rolled up (typical for luthiers using small amounts), get them flat and stable before you even consider making a ply. Be ever so sparing with the glue. When I used to do this, I would also mist the unglued top and bottom faces with water and sandwich in greaseproof paper before pressing. I used to make a lot of pickguards at one time and this method worked well for me. I had no vacuum press. Mine was a wooden screw press. (It still is).

 

[nick1982]

Can you not orientate the grain directions, like actual plywood?

Hi, yes - the grain was at 90' to each other on each sheet.. Are you suggesting trying 45' to each sheet, it would be wasteful but would this work?

 

[nick1982]

When you buy veneers that have been rolled up (typical for luthiers using small amounts), get them flat and stable before you even consider making a ply. Be ever so sparing with the glue. When I used to do this, I would also mist the unglued top and bottom faces with water and sandwich in greaseproof paper before pressing. I used to make a lot of pickguards at one time and this method worked well for me. I had no vacuum press. Mine was a wooden screw press. (It still is).

Hi, Thanks, yes I have done this the same, with a wooden press.

My problem is I am making pick guards for stratocasters, so the area is quite large.

 

[nick1982]

Are there any particular woods that would be better?

 

[NazNomad]

Can you not orientate the grain directions, like actual plywood?

Hi, yes - the grain was at 90' to each other on each sheet.. Are you suggesting trying 45' to each sheet, it would be wasteful but would this work?

I was thinking 90°, so we can rule that out, sorry.

 

[nick1982]

I've just seen something on youtube where a guy used strips to make his plywood, which has given me the idea of cutting my veneer sheets into thin strips maybe 2in. Mixing them up - so it's not just one sheet split and put back together in the same order. Then using a ply method of 45' rotations with 5 sheets. Using cascamite, and leaving in the press for a week.

What do you think? would that stop curl?

 

[profchris]

Have you kept the PVA attempt?

If so you could try ironing it flat, getting it good and hot (too hot to touch but not enough to scorch, tricky I know) and then putting it back in the press until it cools. Wood is a thermoplastic, and so if hot enough it should change shape with the heat. And the PVA will become sticky and then re-harden.

Not worth trying with the Cascamite attempt because that doesn't soften with heat I believe (unless someone here knows that it does ...).

Even so, humidity changes will probably make your laminate move, even if you can get it more stable. Looking at commercial plywood, I notice that the inner slices are thicker than the outer, which I'm guessing might make the laminate more resistant to humidity movement.

Good luck, but I fear you might have discovered why pick guards are usually made from celluloid!

 

[Chrispy]

I think you need to remove the effect of the water in the glues that you are using, it will be causing the veneers to expand and thus causing the warping on drying, to this end I would think an epoxy type would be a better bet.

 

[nick1982]

Have you kept the PVA attempt?

Good luck, but I fear you might have discovered why pick guards are usually made from celluloid!

Ha!!! That has been my train of thought all day!

 

[nick1982]

I think you need to remove the effect of the water in the glues that you are using, it will be causing the veneers to expand and thus causing the warping on drying, to this end I would think an epoxy type would be a better bet.

Ok, that makes sense. that might be worth some investigation.

 

[nick1982]

Have you kept the PVA attempt?

Not worth trying with the Cascamite attempt because that doesn't soften with heat I believe (unless someone here knows that it does ...).

I've used some veneer softener on it and stuck it in the press. Surprisingly it has re- flattened. I'll leave it in there to dry and see what happens.

It appears to be the ash that has made it curl. I think a new method of doing something like a parquet floor might be the way to go. My theory being that if it has multiple smaller cross grains there will be less chance for curling.

 

[Eric The Viking]

This is so obvious that it is probably a silly question, but anyway...

... your individual veneer layers will naturally want to curl one way, as they were cut from the trunk originally (probably). Did your original "sandwich" have those curls opposing each other like this:
( ) ( ) (
or were they curving the same way, like this:
) ) ) ) ) ?

I appreciate that the curls would have been at right angles in the plane of the ply you are making (so the grain of adjacent layers crosses at right angles), but I can imagine how having them all wanting to curl to the same side would encourage cupping, just in an unpredictable way.

I haven't made ply myself, so this is an ignoramus asking!

 

[Racers]

Veneer a piece of aluminium/plastic using PU glue.

Pete

 

[nick1982]

This is so obvious that it is probably a silly question, but anyway...

... your individual veneer layers will naturally want to curl one way, as they were cut from the trunk originally (probably). Did your original "sandwich" have those curls opposing each other like this:
( ) ( ) (
or were they curving the same way, like this:
) ) ) ) ) ?

I appreciate that the curls would have been at right angles in the plane of the ply you are making (so the grain of adjacent layers crosses at right angles), but I can imagine how having them all wanting to curl to the same side would encourage cupping, just in an unpredictable way.

I haven't made ply myself, so this is an ignoramus asking!

I have a feeling it made been the second. )))))

I'm going to give it another go now. but using 1in strips reversing the curl

 

[profchris]

Balancing the stresses will be essential, so ( ) will be more stable.

The amount of wood movement in thin pieces can be quite startling. On a ukulele top which is only 6 inches across and 1.8mm thick, and as near vertical grain as possible, I might see it moving up to 10mm as humidity changes. A flat sawn back might cup twice that amount.

Your veneers are, I presume, knife cut and they will try to move even more, so balancing the forces is the only way you have a chance of producing a stable piece.

But just so you know, I have some commercially made 1.5mm birch ply, and that moves around as humidity changes. Only about 5mm across an A4 sheet, but it still moves.

 

[Droogs]

Hi, have come to this a little late but will chuck in my ha'pnies worth. I'm guessing that the veneer you are using has been sliced on a rotary cutter. This becomes a fairly big factor when using only a few layers. During the cutting process there is a lot of stress placed on the bit of wood going through the cutter and this leads the veneer having 2 very different faces. the top face as it comes off the cutter goes on to be the show face as it is the least stressed and damaged. the bottom face is usually the one we work on and cover in glue. This is due to the fact that it is subjected to the greatest damage, the knife blade causes a lot and i mean a carp load lot of cracks and fissures on the bottom face. This is a problem in a couple of ways. First the veneer want to get back to the shape is was in while in the tree and this microscopic himalyan mountain range vastly increases is open to air surface area and this means a vastly different rate of and ability to accommodate change.
To try and compensate when making your own ply try to have the layers on each side mirror each other. By this i mean have the same show or bottom face of each layer facing out or in.

eg centre bit of veneer and then either side veneer with the show face outwards
The next layer rotated 90 deg and have the bottom face towards to outside etc etc
as you make more ply layers until you have the last outer layer with the show face on the outside.
You can tell which face is the show and which the back by using a very soft touch rub, if not get a young child to tell you which is the roughest side (more sensitive finger tips) and thats the back

Keep the ply in the press for a bit longer than you think you should. after the glue has set wrap in paper and press again to draw out moisture just as you do for flattening the veneer sheet before use

hth

 

[profchris]

If you're still having trouble, I came across a post on a lutherie forum where the author says he uses 1/16 Garolite sheets if he is making wood veneer pick guards.

Garrotte seems to be unobtainable in the UK, but there are eBay suppliers who will sell you a 12 x 6 inch sheet of black epoxy glass, which is what Garolite seems to be, for around £4.

https://www.ebay.co.uk/itm/12-x-6-1-6mm ... 1880475932

If that's being enough for a Strat pick guard it might be worth an experiment. You'd get the black inner, but I don't know whether the glass fibres would be visible.

 

[profchris]

Oh, and this eBay seller sells black phenolic sheet in 1mm and 2mm thicknesses, size up to at least 300m x 300m. I think phenolic is paper fibres impregnated with resin, so might be a little more wood-ilke than the glass impregnated.

https://www.ebay.co.uk/itm/2mm-PHENOLIC ... 1004948064

No promises that either won't curl, but they must surely curl less than wood does!