I've already got an ARTF trainer and a secondhand plane and am now building my first plane (WOT4 Mk 3). The wings are veneer covered foam and the fuselage is a balsa sheet construction (no areas of open frame). I'm looking for advice on how to achieve a really smooth sanded finish to all that bare wood before covering with Solartrim. Any special recommendations on filler, etc. What sandpaper or wet/dry grit nos. I'm very patient and will go through all the stages necessary to achieve a really good looking finish.

I only go to about 100 grit for anything that I'm not intending to sell. The 400 grit school may be fine for competition, but not with a plane like you describe.

I use fine sanding block (the foam rubber covered with grit kind) and just wipe over the model with it. Then I run my hand over it to feel for mismatches of sheeting, then vaccume it and wipe it with a tack cloth.

When I did silk and dope, I went down to 320 grit before final coat, but that was more or less to knock off any fibers before I put on the paper and silk.

Where do you get the silk? Is it heavier than film? Do you use dope to put it on?

100 grit for finishing??? On Balsa? I think Id sand right through my wing sheeting with that. I don't use anything less than 150 grit for finishing, I save 60-100 for block shaping use (along with a hobby knife and plane).

What I do is I first use lightweight filler (model magic, etc) to fill in any dings, scratches, etc. Then I sand the whole surface down with 150 grit on the largest block that works. Now check for any low spots and reapply filler as needed. Sand again with 150 (lightly!!!) and repeat until there are no low spots.

Be very careful with this first rough sanding. If you have thin wing sheeting (like 1/16 balsa) even 150 can sand right through it quickly.

After this I work my way down through 220, 320, and 400 grit, again using sanding blocks. A couple minutes with each grit is all that you need on balsa. Note that to get the best finish, sand with the grain of the wood here.

Once you are satisfied with the finish, prep the surface for covering by vacuuming or wiping with a tack rag (or both).

Finally, take you model out of the shop to cover it. This way all that sanding dust cant get under the covering!

Good luck,
Jeremy

Another little trick is this... Sometimes you come to a piece of balsa that has end-grain showing (usually a wingtip) that, no matter how good you sand it, it remains "fuzzy". Now, you could use some dope to harden it, But it's been years since I've used dope, so I don't have any around, so what I do is thin down some regular white glue (or carpenters glue) with water and brush it on the area. Let it dry overnight, and it cures the "fuzzies". Now, it will sand to a smooth finish.

As the guys say you don't need to use very high grit paper depending on how you intending to finish it. Heat shrink films will cover up a few small imperfections unlike painted surfaces. Once I have everything the correct basic shape I tend to use 180 followed by about 320 and that's it. Wipe down and cover.

I hope you mean you are covering it with SolarFILM, the heat shrinkable film. Solartrim is the sticky back plastic stuff intended only for small areas of trim (as the name suggests).

Be very careful sanding the wing on your WOT 4. The sheeting is not balsa it's very thin obeche. Don't mess about paying a fortune for modelling filler, just get some lightweight filler from a DIY store. You can thin it a little bit with water and paint it on, it dries in minutes.

Good luck - Steve

Thanks Guys, :sunsmiley

This was just what I needed! Yes, I meant SolarFILM (good to see someone is paying close attention).

Many thanks,

Bob (the Builder)

I second that! I use "Elmer's wood filler for light woods". Works like a charm and it's cheap. I've noticed that some of those "super light" fillers tend to melt under the heat of a covering iron.