Cupped Wood

[SSO720]

This question is addressed to all the wood meisters out there. Several months ago I bought a very nice piece of flamed ambrosia maple. It was1" x 8" x 20" and my intent was a bookmatched top on a Telecaster style guitar build.
I did the resaw of the thickness, ended up with 2 real nice pieces, jointed and planed both halves down to 5/16 +/-. It looked beautiful. Since that time it has cupped approx 1/16" and I am now wondering if I will be able to use it.
I have tried running it through the planer again but the cup is still evident. Is it scrap or should I try gluing it up and just clamp the heck out of it and hope it sticks.

[BigguyZ]

It is scrap. Send it to me, and I'll dispose of it properly.

But seriously, I'm no expert, but I'm assuming you're going to laminate it on another piece of wood? If so, is it cupped so badly that it wouldn't flatten out?

[SSO720]

I do think that with enough glue and clamps, it will (I hope) flatten out. Just need to figure out how to clamp the 2 pieces together so I get a good edge bond

[cabinetman]

You might try a veneer softener, like this. It should relax your wood.

.

[mpc]

Thickness planers have rollers inside that forcefully press the workpiece against the table... so any mild cupping is flattened by the rollers BEFORE the workpiece gets to the blades. As soon as the workpiece gets past the outfeed roller... the workpiece is free to relax back to its cupped shaped. A flatbed jointer is the tool to remove cupping - nothing forces it "flat" prior to the cutting knives so the knives can actually work on the cupping assuming the workpiece is thick enough - thicker than the cupping.

Running cupped boards through thickness planers will just give you thinner and thinner boards that are still cupped. Until they're thin enough that they just break while going through the planer.

Without a jointer, you can try making the boards flatter again:
* hand plane

* sanding

* cutting kerfs in the backside so you can flex them... you'll have to use them as veneer in your project - attaching them to something more rigid. If the boards are flexible enough without kerfs, you can try gluing them to a panel. That might lead to future splits/cracks though - "forcing" wood and creating internal stresses often doesn't work long-term.

* splitting the panels into narrow strips that are then re-glued into flatter panels. This probably won't work for you though - the losses due to blade kerfs will make any curved grain lines "disconnected" across the various joints. This technique works better for straight-grained boards rather than nicely figured boards.

How/where have you stored the panels since they were cut? Flipping them over, or better yet flipping them over and placing them on top of thin sticks (so air can circulate around all sides) may help them dry out more evenly and if you're lucky the cupping will reduce after a couple of weeks - that is if the boards are from a fairly recently harvested tree and haven't had a chance to dry fully.

mpc

[leehljp]

That is a great idea Cab! I have wondered if there was something out there for this kind of problem. I have used water on one side to un-cup a few boards and then do all I can to let it dry with weights on top or in a press to keep it flat. It would have been great to have some liquid formulated specially for such needs.

[crybdr]

Like 'mpc' said.....

STOP! Don't run that beautiful piece of cupped wood through a thickness planer ever again. At that thickness, the roller pressure flattens the wood as it passes through the blades. You'll only be left with 'thinner' but 'still-cupped' wood in the end.

This wood 'moved' on you subsequent to your resawing. It will 'move' again....

Do you need to run the cupped face through a jointer...? I'm not sure....it would be nice to have at least one flat face to deal with, especially if you are planning on edge gluing the pieces together. But the material loss may not be worth the convenience.

Like others have said, with some thoughtful and firm clamping, along with a firm substrate...I think this 'rogue' wood could be tamed.

I'd hate to see you 'plane' or 'joint' any more of the material away - when it's not needed.....

[JimD]

You can probably glue it together as is if you put some "culls" across the boards to hold them reasonably flat during glueup. Another thing that helps to minimize cupping is to saw the boards in two down the middle of the cup, joint them to get the edges square, and then glue them back together. You might not want to do that in this case due to the figure but it will cut the cupping way down. 1/16 seems like a "live with it" to me. You shouldn't be able to see it in the finished piece.

Jim

[gsmittle]

You might try a veneer softener, like this. It should relax your wood.

.

Heh, heh. Sorry, couldn't resist.

g.

[cork58]

O.K. ENOUGHT!!~~!~!!

Wood warps because it is not cured right! I had a problem that I posted here that was my 16 X 32 sander. I learned so much from that. It wasn't the sander. It was my overhead heater that caused the problem. I had put the wood on my project table on sitckers as usual, the wood was still a little green. It cupped really bad. I was sure the problem was with my sander and did find a problem. I moved on and found that it was the wood not the sander!!!!! It was the way the wood dried. My heater fins was pointing down at the project table and the wood!!!!!!!! The fins now point up, away from the wood!

To correct the cup I simply put the bow up and watered it allot, then turned it over and let it dry slowly. Wood will shrink and pull its grain to where you want it. You can do this with doors that don't fit quite right as well. If the door is loose on the top or bottom just use a little water to bring it back into shape.

Just my thoughts

[JimD]

Wood also warps just because it is wood. There are residual stresses in the wood from when it was a tree that get released when you cut it. The most obvious example is when you are ripping and the offcut either clamps down hard on the blade or springs out away from the blade. The moisture level has not had a chance to change at that point. Wood will, if allowed, absorb and release water from the air. That also causes movement.

Wood is just not metal. It moves. (actually metal moves a little too but from temperature, not moisture level changes or grain patterns). To make nice pieces from wood, we have to find ways to manage and live with wood movement. In this case, I would probably just glue it up, not try to eliminate the cup on the inside (just on the joint to the sides) and then sand the cup out when finishing the outside. It is harder to cut joints in wood that is not flat but it can be done.

Jim

[SSO720]

Here are pics of the wood I am working with. I have since wet both sides and clamped it to try and flatten the warp. Will see what happens.

[crybdr]

Ahhh...

From the pics, I see that you've already cut the shapes for the halves of the guitar face.....I didn't get that the first time...

Wood is 'alive' and will 'move' depending upon moisture, grain, where it was cut from the tree, etc. It's a truly unsuitable medium for 'precision' work - but that's what makes woodworking fun.

If I was in your shoes, here is what I would do. I'm a newb, so if others disagree...please speak up!

1. Let that wood dry out from the water you have applied. I'm questioning whether or not soaking and clamping will improve your situation - probably not, it's pretty thick - and it's difficult to glue 'wet' wood. I'd bet that when you release those clamps - the wood resumes it's cupped shape. If not, that's awesome!

2. Get all of your material in order and ready to glue - make sure the substrate you plan to glue this to is square, flat, and stable.

3. Run the 'bottom' faces through a jointer (IF you can do it safely considering the shape you have - it's not a rectangular board anymore). This should give you a flat gluing face on the bottom. 'Snipe' is a big issue here, considering you've cut the shapes to size already, so watch for it. 'Snipe' is usually a 'planer' issue, but it can show up in 'jointer' work as well - depending on technique and pressure applied.

4. Run the 'seam' through the jointer using your 'new flat bottom face' as the guide against the fence (again, safety first, considering the shape of your wood). Assuming a 'dead on' right angle of the fence to the bed, the 'seam' should now be square to the 'bottom face', and should result in a flat board after 'edge gluing' them together.

5. Here's where it gets 'iffy'..... You could 'edge glue' the boards together and wait until the joint dries completely. This should take about a day for a strong bond. You need a 'dead on' alignment of the pieces here, to ensure a flat face across the entire 'bottom face' of the board (this has NEVER worked for me - always resulting in 'sanding-out' the slight misalignment). Additionally, the wood may 'cup' in either direction during that time. Hard to know how much it might move....If a 'cup' shows up, and it's MINOR, you could probably force the wood onto the substrate - the edge bond should be strong enough. If the 'cup' is PRONOUNCED, can you bring it somewhere to have it's bottom face jointed? It's a wide piece at this point - not what the home shop can usually handle. 'Snipe' could also show up here - so beware.

Alternative #1, You could try some complex clamping....gluing the 'edge joint' and the 'face glue' to the substrate at the same time. This would be complicated, and I wouldn't have enought clamps to do it right - but it's theoretically feasible. I probably wouldn't try it.

Alternative #2, You could skip the 'edge gluing' and do the 'face glue' of the individual boards to individual substrate pieces. Given the width of the boards, you could probably 'clamp the ****' out of them to reduce some of the potential cupping, relying on the bond between the wood and substrate to create a more stable combination of materials. Then, once both halves are glued and stable, joint 2 faces to give you a square 'edge glue' right down the middle.

As I think about it, Alternative #2 would work best given the tools in my shop. Because you would be working with 'bulkier' pieces, jointing the faces seems to be easier.

Again, I'm just guessing on a fix for your dilemma, and throwing out an idea of what I would do here....Hopefully, others here can add more input and alternatives. The fact that you have the pieces cut to shape already poses a particularly unique problem. And, you haven't done anything wrong, wood moves all of the time.

Good luck,

crybdr

[leehljp]

I know that you have it at about 5/16 or so at the moment and do not know if you intend to keep it at that or sand it down to a thinner face for the guitar or not. However, once most wood gets down to about 1/8", its expansion / contraction and warping can be controlled much more easily.

Wood moves with humidity changes for sure, but have you ever noticed that fine veneer on fine furniture doesn't? Once most wood gets to the 1/8" stage, its characteristics change. Being glued or saturated all the way through with finishes, it is less likely to move or warp. But it must be in the final shape or close to it when finish is applied or glue is applied (as veneer.)