Basswood and warping?

Hello,
I am building a BT-80 size D-Region Tomahawk. For the fins I decided to use 1/8" basswood. After attaching the fins it apperas they warped slightly. Is this a problem with basswood? What causes warping and how do you prevent it?

Thanks,
Brian

Originally posted by bswan72
Hello,
I am building a BT-80 size D-Region Tomahawk. For the fins I decided to use 1/8" basswood. After attaching the fins it apperas they warped slightly. Is this a problem with basswood? What causes warping and how do you prevent it?

Thanks,
Brian

Click to expand...

It's caused by more shrinkage or expansion on one side than the other, due to moisture being applied, or drying one side more. It can happen with most woods.

It may straighten out with pressure. Say, a thick slab of wood over both sides of a fin, squeezed under a clamp or vice grips, and left for a while. A bit of moisture on the concave side might help, but it's hard to know how much is enough and not too much.

Is the basswood stock warped, or did they warp after gluing?

I don't know why this is, but my experience is that "harder" woods are more susceptible to warping overall. That said, balsa *does* warp "easier", but it is much easier to straighten out. Harder woods like ply is very difficult to straighten out once it gets warped.

On basswood, like balsa, I prefer to apply pressure in the reverse of the warp - kinda "over bend" it opposite the warp to straighten it out. This is, of course, assuming that you haven't applied any sealer or paint to the wood yet.

If you're careful not to overdo it and snap the fins or stock, this should take care of it. I suggest doing the bending to straighten them just before applying to the airframe, and then tacking them on quickly with a CA glue. If you cut the fins with the grain parallel to the leading edge, this should do a fine job of holding them straight and allow you to fillet and then finish.



Now, if you applied sealer or fill 'n finish first, well, that's a harder fix. Personally, I'd re-cut the fins from fresh stock and start over.

I do a lot of woodworking and wood needs to be "convinced" that you are the boss.

Try this.

Overbend it slightly the oposite way. Use wood dowels or scraps and clamps and rubber bands and whatever you can find to overbend it.

Clamp it in place and leave it for a few days...preferrably a week or more.

Be patient!

sandman

I've just picked up a couple pieces of 1/8"x4"x24" basswood from Michaels (last 2 in stock) and discovered when I got them home that one of them was warped across the grain. It is still unsanded, unprimed, unpainted, and completely modifiable.

Would it be wise to lightly spray a very fine misting of water onto both sides, then sandwich between a couple panes of glass and stack under some books for a week or so, to "teach" the wood how to be flat again?

WW

Originally posted by sandman
I do a lot of woodworking and wood needs to be "convinced" that you are the boss.

Try this.

Overbend it slightly the oposite way. Use wood dowels or scraps and clamps and rubber bands and whatever you can find to overbend it.

Clamp it in place and leave it for a few days...preferrably a week or more.

Be patient!

sandman

Click to expand...

Is wood just as likely to warp even after it's painted?

When I seal basswood and balsa fins with diluted Elmer's F&F, I coat both sides as quickly as possible (i.e. paint side 2 as soon as side 1 has been under the fan long enough to avoid messing it up). Then, when the pieces are dry enough to the touch to avoid smearing but still obviously wet in the middle, I place them in a wax paper sandwich and press flat under a heavy speaker on a desk. With a little experience, you can gauge the right moment to begin pressing. The pieces feel cool and damp, but the surface seems dry enough that it won't stick or smudge on the wax paper.

In 24-48 hours, the pieces have dried completely, and are flat. Sand and glue in position.

Geof

I'm fascinated by this stuff. We don't have it here- I suppose we'd just select a hard sheet of balsa. Why is it so useful?

Spacecadet

Try Malc at Rockets & Things, he can get most stuff!

ANTICS model shops sell basswood. I think there is a branch in Guildford, and they have an online shop.

https://www.anticsonline.co.uk

Damage

Basswood is my preferred fin material, it's grain is much tighter then Balsa, does weigh a bit more but is less likely to snap on landings. finishes better and takes a lot less "fillers" so the end product weight is almost the same as balsa.

What Sandman said is absoluetely ture, Patience is the key in unfinished woods.
Flying:
After finishing, fins are rarely effected by changes in moisture content of the air.

What other people have said is true. warping is from the changes in moisture content. When finishing the wood's moisture content is basically sealed.

For large wooden nose cones the affect is expansion and contraction (usually it's just contraction ) or shrinkage because the "fresh" wood may have a higher (10% to 12%) moisture content then it shrinks when it stablizes down to about a 7% moisture content.

Warping is caused by the "exposed" side of the wood drying out faster than the other side causing the dryer side to shrink.

Sandman. I have a strange ritual that I go through to keep bulk orders of balsa from warping. When I first get the package, I take it to it's new home (where it's stored) and leave it for a few hours until I think the temp has equallized (sp?). Then, I open both ends of the box and without removing any of the wood, just let it sit for another 24hrs on a nice flat surface. Only then do I remove it and store it. This seems to have cut way back on warpage. I rarely see 1 sheet in a hundered that's warped.

flying_silverad, will this ritual also work for liteply? I will be ordering Four sheets of 1/4"X48"X12" and I'm sure some of it will arrive warped to some degree.


Cliff

John,

What you are doing is what most good woodworkers do.

They never buy wood and start a project. They first let the wood "acclimate" to the shop.


The techniques work for plywood...but not as well. Plywood, especially thin ply, is stubborn.

You just have to be a bit more extreem with plywood.