Somebody asks: "How do I fill the balsa grain?
One or two replies is always: "Use glue! Rub it in and sand it off. I get really smooth fins that way."
I'll be honest, I did this on my first rocket back in 1969. I didn't want to spend 35 cents for a little bottle of the Sanding Sealer that Estes recommended.
After you use a proper filler you probably won't want to go back to using glue on fins.
There seems to be plenty of builders using glue to fill balsa. Maybe I'm missing something?
I cut two small fins from the same scrap piece of 3/32" balsa. I wanted to be sure the balsa grain was consistent between the two pieces.
Wood glue was applied over one side of the fin and smoothed out with an index finger.
Allow to fully dry before thinking of sanding.
Carpenter's Wood Filler is in the next post.
Hrm... I did try using good 'ol Elmer's white glue and din't get get as nice results as I would've had I'd used the dope-based sealer. The fins ended up being a bit "bendy" and sanding was a pain as the sandpaper kept getting gummed up (if applied too thickly - which tends to happen if you don't thin it - but then thinning it would also increase the chance of warping). The result also felt heavier as well.
ReplyDeleteI remember rubbing in some Duco cement into balsa when building "stick-and-tissue" model aeroplanes -- worked nicely to stiffen and toughen balsawood, and it sanded off rather nicely too. The solvents would also evaporate rather quickly so warping often didn't occur. The bad part would be the fumes as well worries about what exposure to solvents would have on your skin (not that such a thought ever entered my mind at that time. Remember the then-common practice of cleaning mechanical parts such as bicycle chain in a bucket of gasoline -- and *not* using gloves?).
Hadn't tried the suggestion of gesso as indicated in the instructions on the kits from Custom Rocket Company.
Back when I was a kid using stuff that gave off fumes wasn't a big deal (as long as I did it outside and downwind) since I lived on a farm. Today however, living in an apartment in the city pretty much means I can't be using the same stuff -- otherwise there would be complaints from the neighbors due to noxious fumes.
And speaking of alternatives -- one thing that I've been meaning to test is using Future floor polish as an alternative to dope (have already been using it for plastic models - works great as gloss undercoat to prepare for decaling and topcoat to seal after applying decals. It also works nicely on clear plastic too as it fills the tiny scratches and the result looks crystal-clear).
Hi Naoto,
DeleteI used Duco when I built balsa and tissue planes. It did sand easily, don't know if it would work filling balsa grain. I was surprised by how many are using glue sticks to apply tissue now.
I haven't noticed using Gesso in the few Custom kit instructions I've seen.
I rarely use Future on rockets, it gets too sticky on humid launch days. I have used it on decal edges, but not over the entire model. I've read that builders use it on plastic model canopies.
Check out Rocket n00b Daniel’s blog where he mentions using a mixture of wood glue and talc as a balsa filler. It needs to be applied to both sides of the fin just like CWF.
ReplyDeleteI have done glue once or twice, but not alone. I tested glue only on some scrap and didn't like the process. I needed a filler to make it more sandable.
ReplyDeleteI've used flour and talcum (as a previous poster mentioned). They both worked, but the flour was a little harder to sand (like cement). It's tedious to do, but it does leave a smooth finish, and has the added advantage of hardening the balsa.
I'd only really use it on either soft fins or something I really needed to harden. Soft craft store balsa does get a nice candy shell with the stuff, which can prevent dings. But it's my least favorite filler.
Hello, yes I tried the wood glue/talcum method after reading your blog entry and it worked pretty good. Still harder to sand than CWF, but not too bad. I only used it on thicker balsa 1/8" or where I've made laminate (3 layer like on the Mega Mosquito) fins.
DeleteI found the wood glue "filler" very hard to sand smooth, not a good option for me.
DeleteI read your blog and the most interesting part is the weight comparison between sealer and other filling methods. I have been weighing my balsa parts after 3 coats of sealer and most of the time they come out lighter than when I started, go figure. Chris has done an excellent job with this blog showing how to build a catalog quality rocket and I enjoy the reads. Personally I have way too many rockets to build so I have really simplified my builds. KISS method of building does not mean lazy or sloppy work. My bench mark for success is to make my rockets look like Chris Centuri builds he posted here before that he built back in the 70s. His builds are clean, fins filled with sealer and perfect paint jobs. Keep up the great work Chris, I enjoy reading your blog.
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