27th Feb 2021, 05:19 PM #1
Veneering - where did I go wrong?
Building a jewellery box-cabinet out of Emu Apple and decided to veneer the doors in case any of it started moving. Sized the veneers to about 2mm thick and glued them to 8mm marine-ply with Titebond 3 using a chunk of benchtop under them and a piece of 16mm MDF on top. Both came out of the clamps as flat as could be so I sat them aside on stickers so they could continue to dry evenly while I continued on with the cabinet carcass. None of the solid boards I sized for the cabinet had moved at all so it went together nicely . . . but when I picked up the doors to size them to fit the cabinet, I found both had a twist of nearly 2mm over the length of them . I've got them bent the other way as pictured at present but I suspect that even if they come out of the clamps flat, the twist will probably prevail and return.
The only solution I see is to resaw the ply out of them and reglue the veneers to some MDF instead (biting my tongue - always said I would never use it!) but that's a lot of mucking about.
Any suggestions for an easier fix . . . . please!
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27th Feb 2021, 05:52 PM #2GOLD MEMBER
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Did you veneer both sides? If so, were both sides laid and pressed at the same time?
27th Feb 2021, 06:21 PM #3
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?
27th Feb 2021, 06:43 PM #4
27th Feb 2021, 08:40 PM #5
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!)
27th Feb 2021, 11:32 PM #6GOLD MEMBER
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- Oct 2014
- Caroline Springs, VIC
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.
28th Feb 2021, 08:07 AM #7SENIOR MEMBER
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- May 2015
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.
28th Feb 2021, 10:17 AM #8GOLD MEMBER
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- Townsville. Tropical Nth Qld.
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?
28th Feb 2021, 02:44 PM #9
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!
1st Mar 2021, 03:13 PM #10
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.
2nd Mar 2021, 01:42 PM #11
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
2nd Mar 2021, 06:17 PM #12
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
-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..
17th Mar 2021, 05:58 PM #13
The magic formula
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)
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