Why sand Lazer-cut Balsa fins?

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Kirk G

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So, if the industry standard now appears to be lazer cut balsa fins for low power rocket kits, why do we bother sanding them?

I don't mean the root edge or the leading edges, cause I understand the need to feather, and/or to remove any small connecting stubbs or bridges that hold them in place in the sheet.

What I don't understand is why we are told to black sand a perfectly good, smooth balsa wood sheet (just prior to punching it out and assembly?

Was this a hold over from earlier kits, where you had to cut it out yourself? Or were balsa wood sheets not always this smooth?:facepalm:

And as long as we're on the subject, how many of your continue to seal the balsa wood before installation with a slurry of wood glue or wood sealer or something similar, before sanding again and building up levels of the filler to smooth it all out?

I'm thinking this is for the perfectionists who need/want a perfect finish. How many just prime and then paint the rocket without filling or sealing first? Does it REALLY make a difference?
 
lazer or die cutting doesnt affect the surface finish. both need to be sanded smooth if you want them smooth...
 
So, if the industry standard now appears to be lazer cut balsa fins for low power rocket kits, why do we bother sanding them?
I don't mean the root edge or the leading edges, cause I understand the need to feather, and/or to remove any small connecting stubbs or bridges that hold them in place in the sheet.
What I don't understand is why we are told to black sand a perfectly good, smooth balsa wood sheet (just prior to punching it out and assembly?
Was this a hold over from earlier kits, where you had to cut it out yourself? Or were balsa wood sheets not always this smooth?:facepalm:
And as long as we're on the subject, how many of your continue to seal the balsa wood before installation with a slurry of wood glue or wood sealer or something similar, before sanding again and building up levels of the filler to smooth it all out?
I'm thinking this is for the perfectionists who need/want a perfect finish. How many just prime and then paint the rocket without filling or sealing first? Does it REALLY make a difference?

There have been a few (nameless) kits where the laser cut fin should have been exactly the same, but they weren't.
Nowadays, you draw a single fin then copy and paste the same image again to make a line drawing for the laser cutter.
In most regular 3FNC or 4FNC rockets all fins should be exactly the same.

I think they recommend sanding the flat surface of laser cut sheets to save a step later on.
Stacking and sanding alike fins goes back to when we all cut fins out with a knife.
I'm building the Mosquito now. Half of the fin surfaces were very smooth, the others needed more sanding.

Do what works for you. After a few more models you'll develop your own methods.
 
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I never sand anything hahahaha. They always turned out good so why start now.
 
Sanding the flat surfaces is only necessary for a nice finish. I used to fly all my rockets naked and never bothered with it. Now I like a nice finish. I sand the balsa (or whatever the material is) then I spray the entire rocket with Rustoleum Filler Primer and sand to remove wood grain and tube spirals. Lately I've also been using Bond Glazing and Spot Putty to fil spirals and other blemishes. If you want to fill spirals and wood grain, then some finishing techniques are in order. If not, then don't bother, and your rocket will fly pretty much the same.
 
I agree with the Barbarian. Sand and fill if it means something to you. If it's "just a rocket" then why bother?? I have some of both in my fleet.
 
why do we bother sanding them?

For looks. The flat surface of balsa might feel smooth to your fingers but the grain is deep enough for paint to soak into and magnify the looks of it. If you don't paint your fins there's really no need to sand them.

You can sand a balsa fin with rough grit and then a fine grit sand paper, and it will feel 10x smoother than when you started. But, if you paint it without sealing it you'll still see the grain show up when the paint dries.

Carpenters Wood Fill will do exactly what it's named for, and fill wood (holes, grain, etc) so that you can apply a finish to it and not be able to tell there was a grain to begin with.

The smoothest finish I ever produced on balsa was a result of:
1) Rough sand
2) Fine sand
3) Paint brush to apply watered down CWF
4) Rough sand
5) Fine sand
6) Coat of primer
7) Rough sand most of primer off
8) Coat of primer
9) Fine sand
10) Two coats of gloss spray paint.

Some people will go further and wet sand their paint between coats for an even smoother finish, but I haven't done that before.

However, if a nice smooth finish isn't important to you there's really no requirement to do all that. There's nobody that will care if your painted fins show the grain except you. The rocket will still (hopefully) fly very fast and high without it. Once you set the rocket on the launch pad and everyone is standing 20' away, your fins will look identical to mine no matter what level of finish we've each done. :)
 
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