Thread: Veneering - where did I go wrong?

Did you veneer both sides? If so, were both sides laid and pressed at the same time?

I'm scratching my head too. It looks like you've veneered both sides, and whenever I've done it like that I've never had any problems. I use Techniglue for that sort of work, but I'd expect Titebond 3 to work just as well.
The only thing I can think of is that part of either the veneer or plywood was a bit damp. I know I'm clutching at straws though. I'd have used ply in preference to MDF too.

Just one thought - was it all clamped evenly over the whole area? If not, perhaps the glue has foamed up near a corner and made the veneer uneven?

Originally Posted by rustynail

Did you veneer both sides? If so, were both sides laid and pressed at the same time?

Yes and yes!

Originally Posted by AlexS

I'm scratching my head too. It looks like you've veneered both sides, and whenever I've done it like that I've never had any problems. I use Techniglue for that sort of work, but I'd expect Titebond 3 to work just as well.
The only thing I can think of is that part of either the veneer or plywood was a bit damp. I know I'm clutching at straws though. I'd have used ply in preference to MDF too.

Just one thought - was it all clamped evenly over the whole area? If not, perhaps the glue has foamed up near a corner and made the veneer uneven?

Clamped as evenly as I could - could barely see for clamps on it (and didn't take a pic). You've got me wondering now if I didn't leave the veneers to rest for long enough after slicing them from the billet. I've got bookmatched slices on both sides of the doors and the twist is in the same direction on both doors . . . so if one pair of the veneers wasn't quite as dry as the others, maybe it has pulled on one side . . . in which case I've got buckleys chance of fixing it I suppose. Wonder if it would have done the same thing to MDF

Have to admit that I've never experienced this, nor have heard of it happening.

Ply twisting is weird.


(ducks!) My secret is that I love MDF. Its the bees knees (/ducks!)

I would have kept them sandwiched between two flat surfaces with weight on top instead of placing on cauls while working on other parts. Just like drying sticks or slabs of timber, weight on top restrains the movement (cupping, twisting etc).

I also would have alternated the grain of the veneer to the grain on the outer layer of the plywood. Effectively making the veneer another layer of ply.

You have used the exact method i use but i usually veneer just one side with .6 material and leave it weighted for 1-2 weeks.

The only thing i can think of is that your veneer is 2mm thick and one piece may have had more tension than the other.

Vern, I am taking a guess here, could it have been the reaction to the moisture in the Titebond seeing the veneers are dry? Would epoxy have been better?
Rgds,
Crocy.

Originally Posted by Kuffy

I would have kept them sandwiched between two flat surfaces with weight on top instead of placing on cauls while working on other parts. Just like drying sticks or slabs of timber, weight on top restrains the movement (cupping, twisting etc).

I also would have alternated the grain of the veneer to the grain on the outer layer of the plywood. Effectively making the veneer another layer of ply.

They were sitting on stickers that I later checked to be parallel and I thought keeping them between the slabs I used during the glue-up might hinder the glue drying properly - something for me to think about next time.
As the outer layer of the ply is less than 0.5mm and the piece of ply was just the right size without hacking into a big sheet, I didn't think it would make any difference - more food for thought!

Originally Posted by Old Croc

Vern, I am taking a guess here, could it have been the reaction to the moisture in the Titebond seeing the veneers are dry? Would epoxy have been better?
Rgds,
Crocy.

Might be christening the bottle of West systems I bought for the next run - don't quite see how it makes much difference but I've seen the epoxy suggested as a better alternative a few times now so I might have to give it a shot . . . just hate using the muck

I have never had problems with either plywood or MDF twisting when the veneering. But I usually veneer:

• in a veneer press, with the veneer between HMWPE cauls, or
• in a vacuum bag, then I leave it on a flat surface (work bench) with a flat caul resting ontop.

My vacuum press is simply one of those catering vacuums used to rwap sandwiches, etc.

Trying to debug your problem:

• could there have been a twist in the plywood before you veneered it? or
• could you inadvertently have put in a twist as you tightenned all those clamps?

I suspect that the 8mm plywood was not rigid enough to act as both core to the veneering and as your caul.

Originally Posted by GraemeCook

...............Trying to debug your problem:

• could there have been a twist in the plywood before you veneered it? or
• could you inadvertently have put in a twist as you tightenned all those clamps?

I suspect that the 8mm plywood was not rigid enough to act as both core to the veneering and as your caul.

As mentioned in my first post, I used a piece of benchtop material on one side and some 16mm MDF on the other side as cauls - no way the ply/veneer could have altered their flatness. The doors came out of the clamps perfectly flat and the twist only appeared some number of days afterwards.


Anyway, after 24hours clamped against the twist the doors were flat again . . . for less than 24 hours so I've sawn the veneers off and resized them - now down to 1.5mm once I got rid of all traces of the glued surfaces.
Now I intend to let them stand for a few days to 'equalise' and head to the hardware to get some 9 or 10mm MDF for the next attempt which leads me to my next question . . .
How do you calculate/guesstimate how much epoxy to mix up for a given area???? Never played with this stuff for anything more than minor repairs etc and don't want to waste too much or be left short and having to mix a teaspoon full near the end of it

Originally Posted by TTIT

How do you calculate/guesstimate how much epoxy to mix up for a given area???? Never played with this stuff for anything more than minor repairs etc and don't want to waste too much or be left short and having to mix a teaspoon full near the end of it

I've been doing this for years and still cant het it right!
I suggest you make a spreader from MDF - just a small piece with one edge cut on 45 deg, with small notches filed in it about every 2mm. Spread it on both surfaces, very thinly.

Immediately before you mix the glue, clean the surfaces with metho or acetone.

I usually mix the Techniglue using various units, depending on the size of the job. In order of increasing size, they are:
-small blob on the end of a spatula
-larger blob on the end of a spatula
-level teaspoon
-slightly 'mounded' teaspoon.

You need to get the amounts pretty right, otherwise you can end up with a sticky blob.
To give yourself more working time (useful if you have to mix up more glue) keep the glue in the fridge. I find the lids of plastic takeaway containers good to mix it up on. After you've mixed it, mix it again, to be sure it's mixed. Then, spread it out on the lid. This helps the heat it generates to dissipate and gives you a bit more working time..

For anyone that's interested, I resawed the veneers off the ply and sized them down to 1.5mm to get rid of any traces of PVA. Got some 10mm MDF and went with gluing one door at a time but unfortunately didn't listen to ALL the advice given to me. Just got it in the clamps with about 30mls left over and went to use the leftovers for a little repair job - red-hot and mostly a solid block already. The door came out of the clamps the next day as flat as a tack so I started on the second door but this time I put the glue in the fridge first - couldn't believe it could make so much difference!! Got the door glued up and was still playing with the leftovers 15 minutes later
Down to the serious formula business . . . Had a look at the 'growth rings' on my PVA bottle to work out how much I used on the doors the first time, forgetting that I did both doors at once, and mixed up 50mls of epoxy which was more than double what was needed. I mixed 20ml for the second door and only had about a teaspoon leftover - quite happy to waste a teaspoonful rather than have to mix another at the last minute . . . and the formula was . . . . 0.015ml/cm²

Hope it helps someone else to not waste so much epoxy one day (Using a Bear brand contact cement spreader)