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Balsa sheet tolerances - is this normal?!

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snrkl

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Just cut 8 fins out of a single sheet of 3mm balsa.

There's a full 1mm difference in the stack height for a stack of 4 fins between the start and end of the same sheet...

ImageUploadedByRocketry Forum1499434652.507084.jpg

Is this normal or have I just picked a terrible place to buy my balsa?!
 

Micromeister

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That's a bad piece of Balsa LOL!
I've had maybe a couple thousandths never anything more.
Sounds like the end of a stacked run?
 
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Nytrunner

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I believe balsa tolerances are +/- a smidge. Given that you're in Australia, it's probably a metric smidge, so that might exacerbate the issue.

Jokes aside, I've even gotten weird balsa thickness from Estes kits. My QCC explorer uses two edge glued sheets to make the fin and there's a noticeable ridge where they join on one side.
 

Cabernut

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I've seen sub-millimeter differences between separate sheets, but not on the same sheet.
 

Kirk G

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Why is this an issue?

Are you planning on gluing them all together, and they must be the same height?

Or are they each a separate fin?

Again, if you can't see the difference until/unless you stack them, why is this a problem?
 

snrkl

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Why is this an issue?

Are you planning on gluing them all together, and they must be the same height?

Or are they each a separate fin?

Again, if you can't see the difference until/unless you stack them, why is this a problem?
Separate fins, I was just surprised, that's all.

I was just wondering if this was normal or had I just found a brand of balsa that wasn't up to scratch that should be avoided in the future.... :)
 

JoeG

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It's a fact that some balsa is better than other balsa. Even from the same supplier. The more picky you are about it the more it costs.

I order the regular run of the mill balsa for the hobby shop here from Sig or Midwest, both acceptable suppliers. Every once in a while I get some nasty stuff. Once I got plywood that was so warped they could have shipped it in a tube. ;)

I just measured a few sheets of 1/8" x 4" x 36" from both companies and they were pretty consistent in having up to about .005" variances along the length. Few were perfect. Balsa can have varying densities even in the same sheet. Have you ever been cutting a piece and hit a hard spot? Varying density combined with humidity and temperature changes from the time it is milled until the time we get it can account for a lot of variance. Also, in their quest to keep costs down, the kit manufacturers are probably not using "contest" balsa in their selection of wood for fins.

Just a rambling observance with limited evidence but vast experience. (I'm old.)
 

snrkl

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Just a rambling observance with limited evidence but vast experience. (I'm old.)
Thanks JoeG - this was the answer I was looking for.
 
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