Brush on thinned CWF with the grain, then against the grain.
Brushing with the grain first gets the filler into the grain pores.
Then brushing against the grain forces the filler in and removes the excess.
There will be brush strokes when the filler goes on and after it dries.
Here I'm sanding down the dried filler with older 220 grit on a block.
TIP: Use the brush marks as a sanding depth gauge. By the time you have sanded down the brush marks smooth, you should "almost" be at the surface.
You should be leaving a very thin coat of CWF on the fins. The fin surface will be the beige color of the CWF.
Hold the fin surface up to a strong light and you might find some leftover brush marks.
You can remove these with some 400 grit.
NOTE: The CWF does not seal wood fins. Water can still be absorbed into the filler and wood underneath.
I was wondering where my comment went. :) Here goes again!
ReplyDeleteI've built several rockets using CWF to fill the fins. On my most recent build I tried out papering (using Avery self-stick labels). I sealed the edges with wood glue (next time I will thin it a bit) and he results were excellent. Even with my still-raw technique, I thought I got better results than CWF with much less effort. which much less total effort than sanding CWF. And papering gives the bonus of extra fin strength.
On your blog you've papered a few fins here and there (not many) but you generally stick with CWF. Given that you've done both, what is it about the CWF method that you prefer?
Hi Neil,
DeleteThanks for re-posting!
I'll paper fins when the balsa is soft or it's a heavier model with trailing fin edges, over the back of the engine mount.
Most all the Estes kit wood is very stiff so papering isn't needed. I don't have fins break very often, usually there is a hairline crack at the root edge joint.
Some of my (early) papered fins have lifted along the edge. I've gotten better at it.
I guess I'm old school, still prefer filling the grain, it's probably a little lighter than papering.
It depends on the complexity model and my mood at the time. If it were a simple 3FNC model with trailing fins, it might get paper. I wouldn't paper a rocket like the Orbital Transport.
I did paper the Flutter-By with good results. I didn't like the ribs running down the fins. The old Centuri instructions recommended papering so it was good enough for me.
Yeah, the edges staying down in the long term is still a question mark for me. I think I'm going to stay with it for a while until it starts failing. :)
DeleteComing from background in "stick-and-tissue" model aeroplanes, I've papered fins using tissue paper (adhered to the balsa using model airplane dope). I also will do a bit of light sanding between each of the first few coats of dope (usually cut to 50-50 with thinner) or primer coats to take care of the "fuzz" that comes up when the paper fibers absorb the lacquer/paint.
ReplyDeleteHi Naoto,
DeleteI also built quite a few Guillow's style kits in my teens. I have used tissue to cover fins before, also for some decorative trim on boost gliders. I was surprised how many use glue and glue sticks for tissue adhesion now, instead of dope.
Paper also has a "grain" along which it's often easier to tear than across it. Keeping this in mind applying in "cross-grain" could also help in strengthening the balsawood part. On occasion on model aeroplanes it's not uncommon to sometimes have double-covering, with the covering material applied in a "cross-grain" layers (basically creating something like plywood, but in paper). Stronger than tissue would be silkspan - which would be a tad heavier and expensive than tissue. Also note, the tissue paper used in model aeroplanes is a bit different that what you find in the giftwrap section of the craft store.
ReplyDeleteHi Naoto,
DeleteI'm aware of the grain in paper. You can find it anytime you tear paper into strips.
I haven't used cross grain layers of tissue. That would be very strong and light.