Can't get the warp out of plywood

[David Masters]

I'm struggling through my first large project, which is building a baby crib/toddler/twin bed from a popular plan. I have a great deal of white oak available to me, which is what I have been using. For the plywood pieces in the plan, I bought a 3/4" sheet of white oak plywood, which was on the pricey side.

After cutting the pieces from the sheet, I stored them flat, but apparently not well, because over the months of delays, they have all developed a slight warp. I would say that the concave is 1/8-1/4" depending on the piece. I've read that applying warm moisture (water in my case) to the concave side and letting the plywood sit in the sun on a flat surface with the concave side down, could straighten the piece as the moisture is equalized across the concave/convex sides. The various recommendations also suggested that the process could go rather quickly. After letting the plywood sit in the sun for a couple of hours (and looking after it every 5-10 minutes), it seems that all I accomplished was to raise the grain a little on the side I applied the moisture. The warp is holding steady at level I started at.

Any recommendations short of buying another sheet and starting over? The plywood forms the structure of the crib/toddler bed/twin bed, and is edged with about 3/4 by an inch of oak. Will the warp work itself out as I secure the edging? Would hate to put everything together and find that the plywood pieces stay warped or conform the edging to the warp.

Dave

[Matt Day]

Is the 1/8"-1/4" concavity over an 8' length or 4' or other?

[David Masters]

Is the 1/8"-1/4" concavity over an 8' length or 4' or other?

The ones I'm most worried about is across about 54" length and one is close to 1/4". The 78" pieces are closer to 1/8".

Dave

[Matt Day]

1/8" over 78" is pretty darn good to me, though I am no expert or cabinet maker who uses ply a lot. If be happy with that.

1/4" over 54" isn't too bad. I wonder if the solid wood edgebanding would help straighten it out a bit? Could you make the edgebanding bigger to help more?

[Konstantin Kalin]

It is not bad at all. Adding solid wood edge banding will make it better . At least this is my expirence to deal with wrapped ply from HD. I use it for my shop cabinets.

[Loren Woirhaye]

A thick hardwood edging aligned with biscuits will straighten it out. Plywood flexes a lot easier than hardwood.

In the future you may want to track down a plywood dealer. They may seem like a commercial warehouse but I've never had trouble walking in and paying with cash or a check. Several years back one dealer I bought from started stocking a ply with 1/10" MDF plies on the outside, right under the veneer. That stuff stayed pretty darn flat and weight-wise it was manageable. Everything I've bought at Home Depot has been inferior flatness-wise to the nice ply I've bought from plywood warehouses.

[fRED mCnEILL]

I build flight cases where the bottom is covered and so I buy the cheapest 1/2" plywood I can. Usually dunnage. Often this plywood is warped. The sheet I had 2 days ago probably had a 3-4 inch warp from one end to the other. It was a hot day so I layed the plywood concave side down on the grass in the sun. In a couple of hours the sheet was almost straight. Works every time for me. Its harder to do with smaller pieces but fro sheets I do it all the time.

[Kent A Bathurst]

No argument with any of the above advice on corrective action - or not, as the case may be - that 1/8" doesn't really get my panties is much of a wad, to tell you the truth.

Moving on - the lesson learned is to cut components when - and only when - you have the time to assemble them. You let 'em sit, you let 'em move.

One other thing - you "stored them flat". Does that mean they were in a stack on a flat surface [aka table saw extension, etc.]? If so, you flew it into the hill - as we have all done at least once.

I do not even want to tell you about the very worst thing I did on this - not like it involved an 84" x 42" QSWO dining table top or anything....................... ......... made out of $18/BF bookmatched wood.....so I won't mention that colossal train wreck that never actually happened. Your thoughts about curve-down storage would have corrected my hypothetical situation, with some moisture on the table top, and some weight to help......and the right assemblage of cuss-words.


If you are going to lay them down flat, you have to - you MUST - sticker them to let air flow around all sides. Or - stand them up on edge as near vertical as you can. Either way, they will be fine until you get back to them.

But still - do not screw around - cut them, assemble them.

And remember - you are not the first guy to ride in this rodeo. Fear not. Bigger problems await you down the road.

[David Masters]

Thanks for the comments everyone. I've lost count of the number of mistakes, but I'm learning a lot.

Dave

[ian maybury]

Just to set out a much less rosy view.

As a person who has routinely bought ply for years without having to worry too much about the details I've been left struggling with similar and worse issues in ply over the last few weeks - building a workshop wall cabinet with the (fortunately narrow) shelves rebated into the sides. Fortunately it's worked out ok - Having thrown out most of a sheet's worth of parts I was able to use clamped on straight pieces etc to hold the new shelves etc straight until the glue dried - the design lent itself to this. I've been left with some very local misalignment, but it's not visual.

The US situation may be a little different, but I bought (from a woodworking/cabinet supplies place that does know better) what in Ireland/UK has been known as WBP (water/boil proof) ply, and had to send it back. It was really badly warped, and full of internal defects (overlaid laminations causing built in stresses causing kinks, gaps etc), microscopically thin outer veneers (sanded through at the edges), variable thickness and pulp like inner laminations. Plus (inevitable given the soggy inner laminations and thin skins) it was floppy - had none of the rigidity of better quality hardwood ply. The supplier offered so called 'marine ply' as a fix, charged quite a lot more and sent me what when cut open turned out to be another pile of junk. Visually better, and probably a somewhat lower incidence of defects - but actually containing all of the same problems. Previous good experience with marine ply many years ago suckered me into using it without first making a careful inspection. My mistake!

This isn't the situation in my experience with well made ply. Good quality material tends to be flat, much stronger and stiffer, and not sensitive to conditions. (that's the whole point of plywood!!) Even everyday quality stuff (like WBP) was some years ago usually of very decent quality. Marine ply back in the day was pretty much an engineered material - dead flat, high quality material and to very tight tolerances with no structurally significant defects. Suitable for doors and the like...

I don't think there's much to be done about kinks and warps caused by internal defects - they are the result of stresses caused by assembly and other errors during manufacturing. Or perhaps of mixed species/moisture contents in the laminations. It's either accept them, or reject some or all of the sheet. The problems often didn't materialise until my sheets were cut open - at which point the piece would kink, or a gap become visible. The warping is for example very likely not the result of anything you did David. Birch ply is typically better, but can depending on the grade and source be of very poor quality too.

As above the US may be different, but investigation here suggests that the essential issue is that unscrupulous retailers responding to house builders/construction users concerned only about price have driven a situation where much of the ply now sold is from cheap Eastern makers, and is either unmarked/to no standard, or is mislabelled (claims to be what it isn't), or more typically misleadingly labelled. (intentionally sets out to creat the impression that it's to some sort of standard when it's not) e.g. has a CE mark suggesting compliance with something or other, but which in fact is meaningless. Quality is typically as above. That's not necessarily an issue if you are putting up a temporary hoarding around a construction site, or covering a hole you've just dug so that somebody won't fall in - but it's another matter entirely if you are cabinet making.

There seemingly is ply made to relevant specifications reliably available from some sources (just starting some research to verify that this is actually the case and not just more hot air) - and some suggest that it's necessary to buy US or European made material of a known brand that's reliably to specification to get quality. It can be very hard to distinguish between the real thing and the fake - and many suppliers here are routinely answering questions in a misleading manner. (but no doubt would claim to be staying within some lot of fine print) With the sort of unscrupulous behaviours we're seeing in the market (and there is effectively no enforcement of regulations regarding mis-selling etc) it's very much a case of buyer be very aware. It's possible (here anyway) to take little or nothing (including labelling) at face value - and unfortunately the well meaning hobby woodworker that's disposed to presume that standards and quality claims mean something (or came up in a different sales environment) is an easy target.

My advice is just to very carefully do your homework. Specify what you need in terms of the relevant standard, and commit to paying more for quality. Then inspect the stuff before use, and if it's not right be absolutely ruthless in sending it back and buying elsewhere. There's a message that needs to be sent, and it doesn't seems to get through by any other means. Perhaps there's scope to report stuff to trading standards/regulators too - although over here that tends to be a waste of time. They put you through every hoop imaginable to document and prove your complaint - and then turn around and do nothing with it, or reject it because the documents don't contain 'proof'…. (heaven forbid that they should have to leave their office to investigate)

I don't like the stuff, but it sounds like maybe composite boards (with MDF cores and the like) may be the future where accuracy and flatness are required - although the same pressures seem have created a situation where there are cheap and nasty (cardboard like) grades of these synthetic materials about now too. The big advantages of ply have always been it's sag resistance and waterproofing, but good quality cabinet suitable ply could well be heading for becoming a premium product produced in relatively small quantities and priced accordingly.....

PS this informative piece by Robert Lang in Popular Woodworking points to most of the technical issues. http://www.popularwoodworking.com/te..._right_plywood He's (i'm presuming) ultimately constrained in his language by the fact that he's writing for a mag. Misrepresentation by re-sellers or at least their walking very close to that line seems very often to be a big part of the situation on this side of the Atlantic. It's perfectly reasonably that low quality ply should be available for applications requiring it, but it gets very difficult when it's pushed as being cabinet grade stuff too..

[Charlie Plesums]

... Several years back one dealer I bought from started stocking a ply with 1/10" MDF plies on the outside, right under the veneer. That stuff stayed pretty darn flat and weight-wise it was manageable.....

Around here that plywood with a pressboard layer under the show layer is called "combi-core" or combination core. It looks more like untempered masonite than MDF to me, but they are similar. It is loved by the CNC cabinet shops since it is so flat and smooth.

I am a solo furniture maker and have found two major problems with it. If I slip when carrying it, a bump or bend sometimes becomes a permanent bulge as the fiberboard delaminates over an area. Not a problem in a large shop with proper space and material handling, but a big problem in my small furniture shop if I am making a bunch of bookcases.

Second problem is that you cannot glue anything to the surface, such as glue corner blocks. Everything has to be in a dado that cuts deeper than the fiber layer, or screwed into the plywood. Even Kreig screws are weakened by the outer fiber layer.

Bottom line, I refuse to accept any "combi-core" plywood.