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Sig Balsa "Box of Blocks" - Making Large Blocks out of Small Blocks

Sig Balsa "Box of Blocks" - Airplanes and Rockets

Sig Balsa "Box of Blocks" 

Matched Sig balsa block pieces - Airplanes and Rockets

Matched balsa block pieces.

Sig balsa block end grain matches - Airplanes and Rockets

Three sections of Sig balsa blocks with matching end grain.

Balsa block sections glued and clamped - Airplanes and Rockets

Balsa block sections glued and clamped. Use plenty of clamping pressure to assure a good joint.

The cost of balsa, like everything else, has been rising significantly since the COVID-19 "plandemic" hit the world a couple years ago. Along with it the price of manufactured kits has gone up as well. A simple 1/16" x 3" sheet of balsa now costs around $2.00 (Sig price). In 2019, you could get it for $1.13 per the stored page at That's a 77% increase. Inflation has been at around 8%-9% (higher in real world numbers) for two years, sapping the life out of everyone. This has been but one consequence of the government-funded virus released from the Wuhan lab, and the psychotic reaction by all the world's "leaders."

Being a scratch builder of model airplanes, I frequently watch e-Bay (very rarely a good deal), RC Universe, RC Groups, etc., for bargains on balsa, but they're getting harder to come by. In fact, you really need to be careful on e-Bay because you'll often see a pack of maybe ten balsa sheets for somewhere in the $30 price range, which is $3 per sheet - certainly no deal.

Balsa blocks have also gotten outrageously expensive. If you have to order a balsa block online, there is a good chance it will end up being more dense (i.e., harder and heavier) than desired. Since local hobby shops (LHS's) are very rare these days, there is seldom an opportunity to go in and look for a suitable block prior to purchase. Sometimes you want a hard block of balsa, but that is very rare in my experience. The only option is to use the less desirable balsa block and hollow it out as much as possible to keep the weight down.

Being tired of paying $3 for a 2" x 3" x 6" balsa block, I decided to roll the dice with a "Box of Blocks" from Sig. No description is provided on the webpage. The 10" x 12" x 15" box arrived as shown in the photo above, crammed full of balsa blocks. They are stacked on-end with most pieces being 3" - 4" long. About half of them are what I might buy if given a choice, a quarter are acceptable for use in some areas with sufficient hollowing, and the remaining quarter are so hard I cannot push a "T" pin into them. Overall, I'm fairly pleased. The only problem is that most requirements I have for balsa blocks for wingtips is for lengths 6" - 10" long. That requires gluing pieces end-to-end. Doing so is no big deal, but having longer pieces to begin with would be nice.

Upon examining the blocks I noted many have matching surface grain that looked like they were cut from the same section of balsa. The end grain pattern confirmed it. After placing the matching pieces end-to-end, they were a perfect match except for the width of the saw blade. Most of the balsa blocks had at least one matching piece, with as many as four matches. I could have glued unmatched blocks together, but then carving and sanding would be made more difficult due to the abrupt change in grain direction and balsa density.

Since butt-end glue joints are not very strong, I sawed all the to-be-joined ends at 10° using my bandsaw, then glued (using Sigment) and clamped them, letting them dry overnight. I would have preferred more like a 15° or 20° angle, but didn't want to waste that much balsa. Besides, once the joined balsa blocks are glued to another part of the model airplane structure, they will be plenty strong. I just need them to be strong enough for rough shaping and hollowing prior to attaching.

Even with squeezing on a large quantity of Sigment on each of the balsa block ends and clamping with heavy pressure, almost no excess glue came from the sides of the blocks. That indicates the very porous end grain easily absorbed all the glue. The same amount of glue on the end grain of even soft pine wood would have resulted in a lot of the glue getting squeezed out. Based on this observation, if I wanted a really strong stand-alone end-grain butt joint for a balsa block, I would use enough glue to have it squeeze out when being clamped. That will assure a good saturated penetration of glue into the wood grain.

I now have twenty-six balsa blocks ranging from around 1½" x 2" to 2½" x 6" that are from 5" to 11" long.



Posted November 19, 2022
(updated from original post on 1/7/2017)

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Kirt Blattenberger, Webmaster - Airplanes and RocketsKirt Blattenberger

Carpe Diem! (Seize the Day!)

Even during the busiest times of my life I have endeavored to maintain some form of model building activity. This site has been created to help me chronicle my journey through a lifelong involvement in model aviation, which all began in Mayo, MD ...

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