In a
recent thread in the off topic section, LucasSpringsteen asked about filling tube spirals. Many methods were discussed but I mentioned how I use primer to do it. This is a method that HCMBanjo mentioned in his blog (I think) at one point, which was a method that George Gassaway came up with. I may or may not be doing this the way George does it, but it's worked VERY well for me and I no longer fill spirals with CWF.
First I make sure I can see the spirals. The spiral that is easiest to see doesn't need to be filled. The other spiral which does need filling is nearly invisible, so I used a pencil to make it show up by drawing on it lightly. Here's the spiral with the pencil mark halfway around.
I used some blue painters tape to mask off about 1/16" on each side of the spiral. This doesn't need to be a super accurate job, and certainly doesn't need to be done with expensive Tamiya tape. The point here is to avoid sanding off as much primer as you can. It's possible to do this without the tape (I've done it a couple of times) but much easier with. Putting tape onto the tube took about 3 minutes.
The primer I like to use best for this is Rust-Oleum 2-in-1 Filler & Sandable. This goes on fairly thick so it fills the gap well, and sands easily when dry.
I sprayed the primer into the spiral VERY close to the tube. Maybe an inch or so away from the surface. This is a lot closer than you'd normally spray primer or paint onto something because you don't want it to drip. But to do this it doesn't really matter. The thicker the better. Because I'm spraying so close I can only get short lengths painted on each pass, so it takes a few minutes to go round and round. It dries fast enough that once I get all the way down the tube I start over and can get two coats on. You can see how far to each side of the spiral the primer has gotten. Not very far at all. This shows you how close I was to the tube when spraying.
About 5 minutes later I took off the tape and the result is a very thick spiral of primer filling the tube spiral. When this fully dries I'll sand it smooth. You can see that there's really not a lot of primer to take off because of the masking. You can also see that I had some runs under the tape, but that's okay. It took about 3 minutes to put the tape on, but that will save about 10 or 15 minutes of sanding.
After I sand the spiral I can spray another coat of primer on the entire tube. After sanding most of that coat off the tube should be really smooth with no spiral, and ready for gluing on fins.