One way of fixing warped balsa sheets

I’m inspired by the new forum here, so I’m going to share the method I just used to salvage a whole bunch of horribly warped balsa sheets. Lets just say that sometimes when you shop at a pricepoint, you get exactly what you pay for.

cough cough

I got used to to straight and even balsa, so I was more than a little pissed when I got my order and fully half of the sheets I recieved were so warped as to be completely useless. On top of that, the width of these “3 inch” sheets varied as much as 1/8", further complicating the process of laying them together to make skins.

Rather than let them all go to waste, I figured I’d try to get them all even and straight, even if that meant losing some overall width.

I made a simple jig using a flat chunk of plywood and some 90-degree pieces I cut from a 2x4. Very low-tech stuff. I attached the 90* corners with a single drywall screw drilled in at an angle. The holes through the corner pieces were oversize so the threads of the drywall only grabbed the plywood underneath. By angling the screw, it supplied clamping pressure on the sheets as it was tightened down. I could then easily loosen and tighten my “clamps” with just a couple of turns of a screwdriver.

Here’s what the balsa strips looked like before working them over. Like I said, so warped as to be useless. This stack pictured here was actually the “good” batch, if you can believe that.

So, I clamped them in and sent them through the thickness planer until all the edges were parallel and straight. I discovered that the pressure of the roller in the thickness planer would actually press out some of the warp as it the wood passed through. Then it would spring back as it came out the other side, leaving much of the curve as it was when it started. I got past this by making sure the balsa strips were clamped firmly together, by taking shallow passes, and by placing the warped sheets with the direction of the curve in such a way that the ends were higher than the center when doing the first side. It seemed to have less tendency to press the curve out that way.

Here’s the first side done.

After the first side is flat and indexed, I just loosened my clamps and flipped all the balsa strips over. In this step, it is very important to make sure all the sides that were just cut are firmly against the plywood base. That’s the only way to ensure the sides are parallel, so I took extra care to make sure everything was flat.

Once they’re clamped in again, just send them a few more times through the thickness planer to flatten the second side. Since I was doing several batches, I watched my ruler on the planer carefully to make sure they were all coming out the same width on the final pass through.

The final result, some still have a little bit of warp to them, but nothing that can’t be worked out as the skins are being laid up. They’re certainly a hell of a lot easier to work with than when I started.

I think this could also work using a hand-planer, it would just require a steady hand and close measuring to make sure successive batches all came out at the same width.


So, the photos aren’t showing up with the new photo-adder thingy…

And I can’t edit my original post above.

Edit: but I can edit this reply post… Hmmm… That means be careful what random thought you start a thread with, you won’t be able to take it back!

Second edit: maybe some html?

<img src=“”>

<img src=“”>

<img src=“”>

<img src=“”>**


Nope, not HTML either.

How about just links?

Funny thing is, I could see all my photos in the original above post when I “preview comment” before posting. Weird…

Yep, them’s some growing pains.

Oh well, I’m sure it’ll be all functional soon.

You guys know where to find the photos.

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Just suppose I loaned my thickness planner to my neighbor and he hasn’t brought it back. For a year or so. Ha.

Could this not be done with a very sharp hand plane in the same fashion? Balsa being soft wood, that is.

We need to find some veneer company that makes it in sheets so you don’t have to piece it all together. That is what I like about the sheet veneers per the WMD thread.

And I am having trouble figuring out how put up pics, too. I did it, but I’ll be darned if I know what of the 15 things I tried that worked.

Still love the new features. Change can be good. After you get used to it.

I’ve done this. It’s not as nice as the above method, for sure! Don’t catch an edge either when you get to the end. I messed up a set of 8 once when I slipped and tore/crumbled the edges on the end. Doing it this way with the real thin ones is even more challenging. Ahh, the lure of power tools is so strong. Someday…