Keeping Thick Glue up's flat

[Michael Necessary]

Greetings All

I've recently glued up some 36" x 36" x 8/4's Red Oak panels to be used as bases for some rolling book displays. I returned after a 2 week Furlough to find all 6 panels warped beyond use, some as significant as 1/2" edge to center. Any guidance on preventing this in the future (see image below)

Many Thanks
Mike

[Michael Burnside]

Greetings All

I've recently glued up some 36" x 36" x 8/4's Red Oak panels to be used as bases for some rolling book displays. I returned after a 2 week Furlough to find all 6 panels warped beyond use, some as significant as 1/2" edge to center. Any guidance on preventing this in the future (see image below)

Many Thanks
Mike

Probably need a bit more details to pinpoint exactly, but some thoughts:

First, before I glued up 8/4 I'd either verify it has been dried or is of very low moisture content. Second, be sure the wood has been acclimated to your shop before milling. Third, if you didn't, you should sticker the panels so they aren't sitting flat against something as the top/bottom would be at different moisture content potentially.

A friend of mine left his tabletop he built on his concrete floor of his shop for a week and came back to a taco even though it was sitting on 1/2" plywood srips. Concrete has moisture in it that will work into your wood :(

[George Yetka]

Also make sure you alternate your grain. And alternate clamps.

[Cameron Wood]

Don't know if it applies in this case, but I think Youtube has done a disservice in portraying the idea that you can just buy some wood, immediately cut it up and assemble something, and expect good results.

[George Yetka]

Mike

Being that you have a single post we are not sure what you do and dont know. People can only guess at your level of wood knowledge.

For a glue up like the one you mention I would buy wood that is dried to less than 10% moisture content and store it in my shop for a couple weeks so that it can acclimate. If the wood were thinner and dried to this point it is less likely to overly move once it is cut/milled the thicker pieces you have can have trapped movement. Once it is smaller or thinner it can twist/cup/curl/etc. Coming from large pieces I mill 80% of the way to my goal and let it sit a few more days before final milling. When it is time to glue I make sure the grain patterns alternate and that the clamps are alternating top and bottom. F style clamps especially will pull your work. Parallel/pipe clamps pull straighter.

[Paul F Franklin]

Assuming you edge jointed the sections before glue-up, it's a good idea to alternate face in, face out on the jointer when edge jointing so if the fence isn't exactly 90 degrees to the table the errors cancel out when glued up. It doesn't take much error to add up across a wide panel.

[John Kananis]

This, especially this.


Don't know if it applies in this case, but I think Youtube has done a disservice in portraying the idea that you can just buy some wood, immediately cut it up and assemble something, and expect good results.

Also, aside from checking moisture, did finish both the top AND bottom?

[Andrew Hughes]

Sounds like another panel that didn’t have edges square to the faces.
Good Luck

[Michael Necessary]

Greetings All and thanks for the input...

Background: I am a 3rd Gen woodworker and now as a retiree, have gone into business full time... slab tables, furniture, built in's, CNC work... I'm competent at the things I do but have rarely worked with thicker kiln dried materials such as in play for this project.

Regarding the project: These "puppy's" were dead flat when I left and had been glued for roughly a week before departure. The source for wood was my go to source who air dried the oak after sawing for 4-5 months before Kiln drying (I think he takes stuff to 10% +/-). clamps were alternated, edge jointed was verified, grains were alternated (for the most part)... These were left in the shop, sanded but unfinished awaiting other components for assembly. They were standing on edge on 1/4" stickers on he concrete floor leaning against the exterior door. Shop humidity is in the 45% range. They had not been acclimating for very long.

My guess as to the cause was moisture (again they were dead flat when I left).

Many thanks for the collective wisdom
Cheers
Mike

[mike stenson]

I'd say wrap em in shrink wrap in the future.

[lou Brava]

I would say you should have checked the moister content prior to fab. (my hindsight is 20/20) You say your source gets the wood to +0r- 10% IMO 10% would be to high and if source saying 10% +/- you could be gluing up stock at 11-12%.

[Mel Fulks]

Assuming you edge jointed the sections before glue-up, it's a good idea to alternate face in, face out on the jointer when edge jointing so if the fence isn't exactly 90 degrees to the table the errors cancel out when glued up. It doesn't take much error to add up across a wide panel.

Agree with Paul . I’ve used some fine jointers , none of the fences would hold square . On thick stuff it’s good to use a cabinet
scraper to take a shaving out of the middle.

[mike stenson]

Agree with Paul . I’ve used some fine jointers , none of the fences would hold square .

I've gotten to the point where I don't even bother to check.

[Richard Coers]

Air movement around glued up panels is critical. Lay them on a bench with only one face exposed to the air, have a weather front move in with really humid air, and you get curled slabs. Learned that lesson the hard way!

[Michael Burnside]

I've gotten to the point where I don't even bother to check.

I check at the beginning of the milling process, but after that, I still assume it isn't perfect. I've never glued up anything substantial that didn't use the alternating in/out technique, even if I ripped the edge on my saw. Knock on wood, but I've never had much of a problem with panel/table glue ups. I've also never alternated the grain, I just pick what looks best. I do recommend keeping the bottom side from laying flat on a workbench, etc, even during glue-up, and keep them stickered for good airflow until they're ready for assembly and finishing.

[John Kananis]

I agree that it's due to poor air circulation. I once took a top out of the clamps early in the morning... it looked great. Right before lunch, I laid it on my cut table (on top of rigid insulation). By the time I finished lunch and got back, there was a curl in the top. Luckily, flipping over for an hour or two "fixed" it. I don't do that any more lol.

[mike stenson]

I check at the beginning of the milling process, but after that, I still assume it isn't perfect. I've never glued up anything substantial that didn't use the alternating in/out technique, even if I ripped the edge on my saw. Knock on wood, but I've never had much of a problem with panel/table glue ups. I've also never alternated the grain, I just pick what looks best. I do recommend keeping the bottom side from laying flat on a workbench, etc, even during glue-up, and keep them stickered for good airflow until they're ready for assembly and finishing.

Since I originally learned with hand planes, folding them together made a whole lot of sense. So I just pretty much continued anyway. I agree, the alternating grain just ends up looking weird and turns into a washboard IME. FWIW, you can either make sure the airflow is completely even, or prevent it. I've had smaller shops, so wrapping pieces in plastic when I was going to pretty much immediately do joinery was a better space solution.

[Jim Becker]

Two things caught my eye in the follow-up post...no mention of cauls during the glue up and the kicker..." on edge on 1/4" stickers leaning against the exterior door. That last part is really a "no-no"...the combination of gravity and moisture from the floor and door (even with the stickers) raises the risk considerably for undesirable movement. If the deflection is minor, the very act of properly attaching them (as table tops) to their bases should bring them flat. It may also be possible to bring them flat by clamping them to a known flat surface with cauls and installing c-channel in the underside (a la Blacktail Studio) to help support them and keep them how you want them. If they are significantly warped, the best solution may be to salvage the material for other structural things by ripping narrower piece that can be brought flat by jointing and thicknessing.

[Richard Coers]

known flat surface with cauls and installing c-channel in the underside (a la Blacktail Studio) to help support them and keep them how you want them.
I don't know where that C-channel commandment came from, but furniture makers have gone for at least a century without them. I hadn't even heard of such technique except for the last couple years on the internet. I have 51 years of experience and have never used a C-channel and consider it a band-aid for those who don't know how to work with hardwood. What I would like to see is some real engineering calculations of what forces wood can apply and if the internet C-channel steel can even restrict the wood force. My guess is the groove cut for the small piece of steel has more to do with keeping the poorly made top flat.

A great article on wood movement. https://kmtools.com/blogs/news/planning-for-wood-movement

[Andrew Hughes]

I agree with Richard. Adding structural steel to the bottom of a slab is the mark of a craftsman without experience or confidence in his work.
Cutting across the grain on the underside of a slab is suicide for the slab to reborn into another project for another generation. So thats a woodworking sin.
My last opinion on table tops is they always look best to me with odd numbers of boards single being the best then 3,5,7 .
Good Luck

[Jim Becker]

Andrew and Richard, I do understand what your concerns are about using C-channel and it's certainly not something that is for everyone and every project. But it is effective in certain situations; particularly large and thicker slabs that need to be stabilized. It does take into account movement because the bolts are in slots and the C-channel I'm referring to isn't wimpy stuff from the 'borg.

Regardless, the only reason I mentioned it is because the OP's situation is to try and rescue something that's thick and bent and it's certainly a valid method...when done correctly. It's also not visible unless you crawl under the table.

[Andrew Hughes]

It’s cool Jim. I’m not questioning your logic.
I also realize I’m a voice in wilderness. I try to stay true myself and just try to share my experience strength and hope. Youtube has a bigger megaphone.
Good Luck

[Michael Burnside]

Andrew and Richard, I do understand what your concerns are about using C-channel and it's certainly not something that is for everyone and every project. But it is effective in certain situations; particularly large and thicker slabs that need to be stabilized. It does take into account movement because the bolts are in slots and the C-channel I'm referring to isn't wimpy stuff from the 'borg.

Regardless, the only reason I mentioned it is because the OP's situation is to try and rescue something that's thick and bent and it's certainly a valid method...when done correctly. It's also not visible unless you crawl under the table.

Sound logic. I’m not one to begrudge modern techniques in woodworking. I have my own personal limits/opinions but since I use CNC in a lot of my pieces I’m probably a bad example LOL.

Honestly I don’t think it says much about the woodworker either way. What matters is what people think and feel when they see/touch a piece of craftsmanship. I’d rather be judged by people that love furniture rather than a pack of woodworkers ;)

[Kevin Jenness]

The panels were flat to begin with so the cupping was caused by a change in moisture content. With the shop rh around 45% the equilibrium moisture content would be about 8%, so if the wood was at 10% or higher initially that would explain the problem. There may also be an issue of gaining moisture from the concrete floor.

When I have to put a project on hold like that I either sticker or dead-stack and cover the parts. I mostly use material that has been in the shop for long enough to acclimate, which is more than one might like with 8/4 oak. With new material it is a good idea to use a moisture meter before processing. Material that has a likelihood of moving should be covered between working sessions and finished as soon as possible.

These parts might have been usable if joined to the rest of book display components right away. They still might be salvaged by wetting the convex side or drying the other- or resorting to steel reinforcement.

[mike calabrese]

Just to add another point of view outside the moisture comments which I agree as an issue.
The other contributing factor in bent glue up panels is clamp pressure and attachment.
When clamping panels using a ton of pressure is a problem.
Ideally when glue is applied to properly milled panels we use whatever pressure needed to bring the panels into full contact and get the desired glue squeeze out.
Once that is accomplished to satisfaction we back off the clamps retaining sufficient pressure to keep the panels together. We kind of gage this by cranking enough pressure into the clamp such that it will not slip off when the panel when we try to take panel weight onto the individual clamp and not have it slip off the panel.
Additionally if you apply clamps such that the lip of the clamp is the gripping point such that the pipe is well above the panel you will induce the condition you describe. This is especially true even if you alternate the clamps on both sides of the panel. The vids below show some methods to prevent warping the panels using cauls etc. I like to set my pipes against the panel using a barrier to prevent glue stain from the metal pipe. We use coroplast (plastic cardboard) pieces between the pipe and the work.
There or all kinds of other barriers that can be used as simple as wax paper, packing tape wrapping on clamp pipes .

In short it is my opinion to have a feel for the walk away clamp pressure that is enough to solidly hold the work but light enough mot to induce mechanical deformation.
calabrese55

https://www.youtube.com/watch?v=aACwqhce_qQ
https://www.youtube.com/watch?v=qYoz16DeD9k
the parent string https://www.youtube.com/results?search_query=clamping+large+wood+panels

[Jim Becker]

When clamping panels using a ton of pressure is a problem

This is a really important point that I've only started to realize as such recently. For many years I thought that cranking the clamps was "necessary" for a good glue joint when in reality it can add additional stresses that in turn can cause more issues. If one prepares a good edge on each component, "reasonable" clamping pressure with over/under alternation to balance the pressure and use of cauls to help with flatness results in a decent panel the vast majority of the time. So tighten them up to bring things together, but don't get "the Hulk" cranking them down for you.

[Michael Burnside]

This is a really important point that I've only started to realize as such recently. For many years I thought that cranking the clamps was "necessary" for a good glue joint when in reality it can add additional stresses that in turn can cause more issues. If one prepares a good edge on each component, "reasonable" clamping pressure with over/under alternation to balance the pressure and use of cauls to help with flatness results in a decent panel the vast majority of the time. So tighten them up to bring things together, but don't get "the Hulk" cranking them down for you.

100% agreed. I've often just "clamped" with blue tape and not just edgebanding :eek:. During dry assembly, if I have a fitment/gap issue, that's where I fix it. I don't try to compensate with gorilla strength and crank down clamps. When you do that, remember glue has water in it. Water is highly incompressible so all that pressure you're giving, cranking down on a clamp, is translating to the wood/joint, not the glue.

[Warren Lake]

skip the first you tube anyone clamping on a bench doesnt get it.

Second guy has two pieces of wood set on the bench, that is correct. You dont need the cauls. to make flat you need to make it flat by your clamp placement. You have wood sitting on two beams if it raises up or goes anywhere other than flat then you have not put your clamps properly or done up too tight. If your edges were machined properly then its all about clamp placement high low angled whatever. Dont find I need cauls though they help with align from board to board but cauls just disguise the clamp placement and what affect its having on straight or not.