Boards cupping with glue-up

[Bruce Mack]

I'm making a 16 X 24" serving tray using curly oak as the bottom. I have a 1' thick 5 1/2 inch wide board that has acclimatized in my shop >10 years. I tried to get 4 boards from it but ended with three usable ones of different thicknesses. After planing and some replaning because of tearout I had 3 boards with good figure. They were ~1/8' thickness and lay flat on the 1/8" Baltic birch which was to be the substrate. The edges met neatly with no gaps. I was happy to have something that even with the sides would not be overheavy. After rolling the PVA glue onto the birch and laying the oak pieces I had rapid cupping, with convexity of the oak surfaces in contact with the glue. I weighted the panel with a granite surface plate and a few pieces of steel in the hope of some planarity when the glue-up dried overnight. It has remained a washboard after my halfhearted heating of the panel with a heat gun and further compression pressure. I plan to resaw more boards a little thicker and with a new blade.The additional thickness will give me a little wiggle room to correct tear-out, but no assurance against cupping if a water-based glue is used. I'm thinking slow set epoxy. Polyurethane glue is messy and the spritz of water may itself cause some cupping. Am I missing something I should consider? I do not have or wish to buy a vacuum system or use toxic adhesives
The extreme separation is partly the result of my unsuccessful effort to salvage the oak. ItD6717DAE-3F91-4CDB-95CB-CBFF57DEC7CD.jpg488EDA0C-B0B8-4526-B7D4-C6768E3D1EB6.jpg was ugly before that effort.

[Andrew Seemann]

As you suspect, the water is causing the oak to expand. The plywood can't expand, or at least not as much, due to the cross ply.

I'm not sure if you can make that design work, usually a veneer would be much thinner, so the substrate can overpower the the veneer. For your tray, the oak is the same the thickness as the plywood. Even with a non-water base glue, it will still have problems.

In our climate (wasn't it 50 degrees warmer a couple days ago?) the oak and plywood will forever be at war with each other, unable to agree on what size to be, and forever twisting, cupping, and trying to separate. Even if you bumped up to 1/2" plywood, I think you would still have problems with 1/8" veneer.


As an aside, one of the traditional ways to cut stone, since you bring up granite surface plates, was to drill a series of holes in the stone, pound in wood stakes, and then pour water on the stakes. The pressure from the expansion of the wood was so strong, it would cause the stone to crack along the lines of holes. Just letting you know what you are up against with the power of expansion in wood

[Richard Coers]

I can't figure out if you only glued the oak to one side or both. You have to do a balanced layup so both sides are equal. I was taught that any shop cut veneer has to be around 3/32" from the boards and then finished to 1/16" to act like veneer. Go thicker than that and it acts like solid lumber. There is more movement with flat cut boards than quarter sawn and rift sawn.

[Jim Koepke]

Will the finished panel be held in place by slot?

It might be possible to put it together without glue or just a dab of glue in the center.

jtk

[Kevin Jenness]

That is a pretty thick veneer, especially for flat cut oak. 3/32" is about as thick as I use on a substrate that restrains the veneer.

To get a flat result you need to veneer both sides and get the glue and clamp pressure on before the veneer has a chance to expand and curl. A glue like Unibond 800 or epoxy with little or no water can help. A thicker substrate or thinner veneer would help.

You can saw your boards thinner and run them through a thickness sander with no worries about tearout. If you can resaw them cleanly enough you could lay them up with epoxy and sand them afterward.

To do this over with epoxy and weights you need a waxed flat base and top caul thick enough to spread the pressure evenly. Be sure to sand the mating surfaces with 80#. Pull the joints together with clear packing tape and run tape along the seam to prevent squeezeout. Do a dry run to be sure everything lays flat.

[Lee Schierer]

If I read your post correctly you resawed a board to get four pieces, but only ended up with three that were usable. Then you planed additional material off the cut side to get them acceptably flat. Then you applied glue to one side to bond it to the plywood.

A couple of suggestions. Whenever you resaw any piece of wood, weight, stack and sticker it to allow it to adjust to the ambient moisture for a while (several days-week) to insure it stays flat. The internal moisture level changes much more slowly than the exterior. Since we just went from fall, which is usually damp to winter where our heat system dries out the air, there was an ambient moisture change in your shop.

Second thought. When planing wood surfaces, it is always a good idea to remove equal amounts from each large face area whenever possible. This helps reduce the cupping.

Since we know that moisture from glue causes swelling, it would have been advisable to dampen the exposed side at the same time with distilled water to equalize the wood.

[Bruce Mack]

Thanks everyone.
Lee - in my usual slow mode, I let the boards lie in my shop for about 3 days before the glue up. I have seen slices from unseasoned pine curl like a potato chip. While the PVA released some demon, I suspected no problem before the glue-up. When I noted the cupping, I wish I had spritzed the exposed side then. I'll keep this in mind.
Kevin - I should have changed the blade before resawing. I had not used the bandsaw for that task in a long time. I'll try thinner next time. Not having a thickness sander, I'll just take the slices and lay them up with epoxy, scraping and sanding afterwards. Great suggestions in your last sentence.
Jim - I am trying to do a one-off of a designer tray as a gift. I haven't thought about the sides for this piece. Google "Michael Verheyden oak serving tray with hammered bronze handles". Mine will be minus the bronze and, sadly, minus the craftsmanship.
Richard - I glued the oak to just one side. The Baltic birch stood up to the stress like armor plate with no rippling. I think I did not apply enough glue with the roller as the glue had started drying. I should have used Titibond Extend to allow myself time.
Andrew - it does look like warfare (and my ineptitude). It's funny about Minnesota climate changes and wood splitting stone. Maybe my recipient, also in Minnesota, will like her hygrometer tray that moves with the seasons.
To everyone - thanks for the unexpected (by me) observations! There's a lot to think about. I'll post if I ever finish this.

[James Pallas]

Age old thing. Thinner veneer and lots of pressure. Just looking at a veneer press is scary. I know vacuum works for thin veneer but a press measures in tons not pounds. Thin your veneer and try again.
Jim

[Bruce Mack]

Age old thing. Thinner veneer and lots of pressure. Just looking at a veneer press is scary. I know vacuum works for thin veneer but a press measures in tons not pounds. Thin your veneer and try again.
Jim

I'll do that. Thanks.

[Andrew Seemann]

Hi Bruce,

You can run the veneer through my thickness sander if you want. I'm just a few miles south of you in Mound. PM me if interested.

[Robert Engel]

The veneer did what all veneers do. I think the problems started with you not using it right away and not clamping it.

You don't need a vacuum press. Make some platens, 2 sheets of 3/4 MDF top of veneer/1 sheet under plywood, stout cauls (I would use 2x4's) space about 6" apart. Clamps all along the edges about no more than 4" apart. If the panel is wide cambering the cauls is a good idea.

Next time, go straight from resawing to gluing.

[Bruce Mack]

Nothing can stop an old man with time on his hands. Although I may eventually put a new blade into my Delta bandsaw and saw thin veneer, I still see my misadventure as a work-in-progress. I first glued the entire periphery of my panel to the Baltic birch by squirting PVA glue into the gaps and using spring clamps to create contact. These small clamps when appropriately spaced apply considerable force. Then, recalling how I used to dry-mount photographic prints with an iron as well as an article on applying veneer pre-coated with PVA glue using heat to activate the dried glue, I bought a steam iron and tried to glue the long edges. A lot of heat (with steam to avoid scorching the boards) worked briefly but when I removed the granite surface plate used to apply pressure I saw that the edge gluing still had gaps. Moreover the edges still lifted from the plywood backing. I flipped the panel and did shallow rip cuts to enlarge the gaps to slightly less than 1/4". Next I will squirt glue into these gaps and press the edges to the baltic birch using cauls with a slight convexity that I made yesterday. They are sections of a 2x4. The cauls will be held with f-clamps from hell, two 12" Piher Maxipress F piston clamps which arrived yesterday in a box weighing 13 pounds. I'll do one joint at a time, thinking it will make setup easier and a lot cheaper. The clamps are self-indulgence and overkill but they are beauties https://youtu.be/I5Gbi_DXOUY.
If the glue-up holds, I'll inlay the channels with either quarter-sawn oak or ash.
IMG_1792.jpg

[Bruce Mack]

I eventually got a flat panel by crossbanding ash strips on the back of the thin Baltic birch to remove the cup and some other sleight-of-hand to deal with longitudinal bow. I just saw Luke DuPont’s post “Oh hey, wood moves!” but I think I’m spared by the interposed thin plywood. Also my wood had already moved and I hope that’s that (the power of magical thinking). When I cranked down on the cross bands at each end I heard “crack.” I have a few narrow splits at each end that follow the figure of the curly oak. I think that epoxy dyed black will make a neat accent. Perfect is the enemy of good, maybe. The wood still has to be sanded and cleaned up, complementary strips have to be inlaid, everything has to be stained and Tru-Oiled, and the frame of the serving tray has to be made. This can be fun when you’re not doing it for a living.

[Tom Bender]

The adventure may continue when you stain. There may be adhesive in the joints and cracks and soaking thru that interfere with the stain. If you seal first it should help but then you will be coating instead of staining. Practice if you can on similar stock.

[Bruce Mack]

[QUOTE=Tom Bender;3173038]The adventure may continue when you stain. There may be adhesive in the joints and cracks and soaking thru that interfere with the stain. If you seal first it should help but then you will be coating instead of staining. Practice if you can on similar stock.[h hi Dr./QUOTE]

Thanks, Tom. Your comment prompts me to think harder. Glue creep under cauls has plasticized some areas. I’ll go after what I see with card scrapers followed by sanding of the whole surface. I hope to locate subtle areas with paint thinner. I’m thinking of Zinsser Clearcoat with amber liquid dye added followed with pumiced TruOil for surface protection. I will try this first on cut-offs.