why are my boards cupping?

[bob]

I am building a kitchen hutch out of primavera, also known as "white mahogany". The wood was purchased from an importer with a kiln, so it is kiln dried. I milled the wood to 3/4", glued up a bunch of panels roughly

16 inches wide, composed of 3 boards 5 to 6 inches wide. All was well for a couple of weeks. Then, when I started assembling the hutch, I discovered my panels are cupped across the grain - roughly 3/16 of an inch across 16 inches. Not all of them are cupped, but perhaps half of 20 panels are. The moisture content is 12 to 14%, which seems high. I can't tell any significant difference between cupped and uncupped panels. My genuine mahogany and some oak, also stored in the shop, both measure around 8%. I've noticed that the cupped panels will "uncup" over a few days, then re-cup.

Any ideas why this is happening? Are the panels useable? I'm thinking not.

Also, when you glue up panels, should they be stickered while stored? I've always just stacked 'em up on some sawhorses or whatever is handy.

This is the first time I've worked with primavera, so maybe it's just not a good species to use for furniture...

Thanks.

Bob

[Lawrence L'Hote]

--snip---

I've used primavera for small tables, clocks, doll cradles and other stuff. I salvaged the wood from crates that came from Costa Rica. The wood is soft(similar to pine), exhibits some incredible grain patterns, is easy to work, but has problems with finish splotching and moisture absorption. The breadboard ends of some 28" table tops in my living room are presently about

3/16" proud of the table edge both front and back. The house humidity is, right now, about 50%. The slight cupping you are experiencing is probably typical of the species. The wood is used for fine furniture and veneers. FWIW The Farnsworth house designed by Meis van der Rohe uses primavera for all the interior wood work. Some of the wood paneling is over an inch thick and VERY wide. See space down to interior views of cabinets. The house is in a very humid area along a river but has a.c. The paneling uses very select primavera that is straight grained. I noticed no distortion of the cabinetry when I visited there back in August. From my experience I've found the wood to dent and scratch easily and, probably, would not use it in an area that was subject to a lot of people contact. I would be interested in any other experiences you have with this stuff and please post any pictures(or links) of your progress. Larry

[MikeG]

12% MC for furniture making is high. It should be around 8%. Just because the importer and the wood was kiln dried doesn't mean it was kiln dried properly. Did you check it before you bought it?

If, in fact, the wood was at around 8% when you bought it and now is at

12%, of course you should have stickered it. Then there is the environment the panels were stored in and the environmentt that you kept the individual boards in before working them and how long before and after milling they sat. Were the boards stickered and allowed to acclimate to the new environment of your shop before and after milling?

Those are just a few of the things that can go wrong and then there is the fact that sometimes wood just takes it into it's own mind to warp no matter what you do.

[J. Clarke]

FWIW, the FPL database says of African Primavera that "movement in service is rated as small". That is the normal commercial species. However there are also four different South American "primavera"s, and given the amount of wood that seems to be coming in from South America these days it could be one of them instead. The most common is a relative of ipe and if it's anything like ipe should be pretty stable and pretty near indestructible, but the other two I can't find any information about.

[Lazarus Long]

I just experienced such a problem with a cherry panel. However, I figured out that the heat register directly over my work in progress had been blowing on it for a day, resulting in one side drying more than the other, viola! Cupping! After a couple of days with cauls clamped to it, it equalized and returned to flat. At that point, I finished panel construction which in this case was to put breadboard ends on it. That'll hold 'er.

So it is with your panels. They're drying unevenly. Keep them stickered if you can't get them assembled right away. And that's the best advise - What I try hard to do when I build solid panels like that is get them installed/assembled together as soon as possible. The resulting assembly with all it's glue and joinery properly done ought to hold them in the shape you want.

And you ought to start with wood whose moisture content has stablized to the conditions in your shop. The seller may have dried them then stored them poorly, or not dried them right.

[bob]

Thanks, guys for the great advice. I have, unfortunately, decided to abandon this project with this species. I do not have time to quickly glue up, then assemble the project. Things are going to sit around. My shop is in my basement - a walk out garage. No heat vents around, but the temp stays very comfortable year round, even down here in the Deep South during the summer. I'm inclined to think that this species of wood just sucks up moisture. I bought the wood in May and it's been sitting around for three months or so before I started milling it. I am really concerned when I leave a panel lying flat on my bench and a week later it is cupped. No, I did not sticker it during storage or milling. I need to start doing that.

A lesson learned for me. I've still got 200 BF of primavera to do something with......

[Swingman]

Before you give up do one more test. Take one of the cupped panels, rip it in half, flip one side over end-for end, then glue the panel back together.

This may make the "cup" negligible and let you proceed with the project without wasting all that stock and time.

You may also let one of these ripped and re-glued panels "sit around" for awhile and see if that doesn't help the problem.

It was species of wood like this that the technique of alternating grain direction of the individual boards in a glue-up was developed.

That said, any type of wood may distort in some manner if not used soon enough after milling and, as you've noted, your way of working may just not be compatible to the type of wood you're using.

Good luck ...