Some Questions Related To Fit and Finish...

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lakeroadster

When in doubt... build hell-for-stout!
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Couple of questions:

  • What grit sandpaper do you use to sand down the CWF?
  • Do you chuck the nose cone into a drill press to sand it, thus to ensure profile?
  • An idea came to me for the cockpit (see photo below).. since it's simply a small contoured balsa piece, couldn't I glue it to the body with wood glue and then simply seal it with CA?
  • Do you folks rough up the body surface at balsa attachment points, or is that not required?

As always, thanks for helping me through my BAR phase
 

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For most of these questions there is no one right answer. Here's my take:

Couple of questions:

  • What grit sandpaper do you use to sand down the CWF?
When possible, I'll do a light sanding with 220 to remove the bulk of the stuff, but take care not to go all the way to the wood. Then I'll finish with 400. If it's too risky to have at it with the 220, I'll just do the whole thing with 400.

  • An idea came to me for the cockpit (see photo below).. since it's simply a small contoured balsa piece, couldn't I glue it to the body with wood glue and then simply seal it with CA?
Sure. I'm personally not a fan of sealing with CA, because I find it hard to sand. But it'll work. I do use it for sealing balsa nose cones, and the inside edges of body tubes, and a few other places.
  • Do you folks rough up the body surface at balsa attachment points, or is that not required?
Not required but it often is a good idea. Or, you can peel off the glassine layer under the root, leaving uncoated and very glue-thirsty paper for the joint. I have done that on occasion but usually don't bother.


 
For the fins use the double glue method.

Apply a layer of glue to the fin and place it on the tube where you need it - and then remove it.
Wipe both the fin root and the tube so only a thin layer of glue is left behind. Let dry a bit. Different folks will have different ideas from 30 seconds to 30 hours :)wink:)... I found just a minute is sufficient.
After the time is up, apply another thin layer of glue to the fin root.
Carefully line up and place the fin onto the tube. It will grab quickly and have limited ability to adjust.

This creates a very strong bond.

Then add a fillet to both sides of the fin/body joints.
Typically the balsa or tube will fail before the glue joint will


Also, I have used thin CA to seal and harden balsa. It can be a little more difficult to sand, but it adds a lot of strength and can make an almost plastic smooth finish

Just watch out for the fumes and don't put it on too heavy as it can run
 
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220 as mentioned is a good start to sand down the CWF and follow with 320 and depending what kind of results you want 600. I use thin CA to seal balsa nose cones.

Put a small puddle on a sheet of plastic like a zip lock or something similar. Starting with the point of the nose cones roll the nose and as you do it lower the angle until tyou covered the entire surface. Sand with 220 and then repeat. Usually twice is all you need. The final sanding should include 320. Spray with HBP and your basically done. The nose cone has a hard shell finish.

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