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  #21  
Old 03-19-2016, 10:59 AM
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Continued...

If you want a TERRIFIC finish, you'll probably want to damp sand. I start by getting a roughly 2x4 inch piece of 400 grit wet/dry sandpaper, a small (disposable or non-eating-out-of-it-from-now-on) bowl of water, an old towel, and a couple paper towels. To damp sand, dip the paper into the water, then shake off the excess water or daub it on the towel so the sandpaper is very damp but not dripping wet. Then sand the surface in SMALL OVERLAPPING CIRCLES, while simultaneously ROTATING THE PART IN YOUR HAND. DO NOT sand in straight lines back and forth, or sand in the same spot continuously... ALWAYS keep the sandpaper moving, and rotate the part so that you're not sanding in one spot, which creates flat spots. DO NOT put too much pressure on the paper-- let the grit of the paper do the work, slowly grinding off the surface of the primer or material. (By the way, these are the sanding motions and principles you should use on ANY sanding, wet, damp, or dry, shaping balsa or doing fine finishing work). As you damp sand, you will notice the particles coming off the surface will combine with the moisture in the paper and start to form a thickening "sanding mud" on the surface of the part and the paper... as you continue to sand off more particles, this will get thicker and thicker. After a couple minutes, dunk the paper in the bowl of water, and rub your thumb or fingers over the surface of the grit-- this will dislodge the trapped particles and wash them away. If you want to inspect the surface, gently wipe away the sanding mud with a damp paper towel, and then dry the surface with the dry clean paper towel... or you can continue damp sanding until the entire surface has been damp sanded and then clean and inspect. Just keep repeating the process working your way up the cone, rocket, whatever until you get to the end. Clean it off with a damp paper towel to remove all the "sanding mud" and then dry the slightly damp surface off with a dry, clean paper towel. Inspect the surface by holding it up between your eye and a distant light source-- a brightly lit window, lamp, chandelier, etc... Look at the "glint" of reflected light on the surface of the tube or cone, and inspect how that glint looks... if you can see waviness, pits or imperfections or low spots, nibs or hard particles or high spots, and SANDING SCRATCHES, they will ALL be visible in this glint of reflected light. You probably won't be able to feel them or see them looking at them directly, but the reflected light acts just like a laser reading the tiny hills and valleys in a CD or DVD, showing things you cannot see directly. If the reflected glint is perfectly smooth, the surface is done. If you can live with any imperfections you see, you're done. Allow the parts to dry for an hour and you're ready to paint.

You CAN still ruin the surface at this point by misapplying the paint... paint in thin, quickly and evenly applied coats to prevent the dreaded drips, runs, and sags. Avoid "dry spray" and "orange peel" through proper distance of the spray from the surface (not too far away) and runs and sags by not getting too close to the surface or spraying too heavy a coat. If you apply the paint properly, there is NO need for any 'color sanding' of the final paint coat-- it should flow out evenly and smoothly on the surface without any flaws or blemishes at all... and you'll have a GORGEOUS finish...

I paper my fins with printer paper and white glue, and most rocket tubes are glassine, so even fins and tubes can be "damp sanded" for great results... the key is to remember your DAMP sanding, not WET sanding... the only moisture should be on the paper and the very surface of the primer being sanded... there SHOULD NOT ever be water "dripping" off the rocket. Wipe off the surface with a damp paper towel periodically if you're worried about moisture buildup (and to get rid of the 'sanding mud' before it dries out and is hard to remove). The sanding mud actually helps the sanding, BTW, because it "polishes" the surface as you sand-- you can actually get a mirror finish in primer using damp sanding if you try! Of course you don't really WANT it THAT finely polished, as you want SOME "tooth" for the paint to grip the surface of the primer, meaning it should be slightly dull... Don't sand with too much pressure to avoid sanding scratches, which are hard to remove and will show through paint. Sanding in a small overlapping circular motion and keeping the parts your sanding moving (or move around on the surface constantly) and avoiding "straight back and forth" sanding motions (to the extent possible-- sometimes you "have to" up against fin roots/fillets and launch lugs and stuff) will give the best results, regardless of damp or dry sanding. How far you take it and how good you want the appearance is up to you... you can quit at "looks good from 15 feet away" or you can put a museum-quality finish on a rocket if you desire, I've done it, so can you if you want...

I've got some build threads and incorporate papering fin tutorials and hardening balsa tutorials, and primering, sanding, and damp sanding tutorials in them... look for the "Dr. Zooch beta-build" threads I've done... If you want links lemme know and I'll look them up...

Later and good luck! OL J R
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  #22  
Old 11-06-2016, 08:15 PM
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Quote:
Originally Posted by luke strawwalker
The Walmart "Color Place" red and grey primers do an excellent job for me, and they're 99 cents a can...

Otherwise, I use the Rustoleum high fill autobody wet sandable primer... good stuff!

later! OL J R

Second this opionon. I use it alot cheap and drys fast.
But still cant beat the end result of filler coat and sanding sealer dope.
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  #23  
Old 11-12-2016, 07:52 AM
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When I use primer for filling balsa and priming tubes, I use either Duplicolor, or 3M/Bondo light gray primer. Both are lacquer based, dry very quickly, and sand great. I've found Rustoleum clogs sandpaper more quickly, so only use it when I need a white primer. I can still get Aerogloss Sanding Sealer from my LHS, but only use it on small models.
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  #24  
Old 11-12-2016, 08:41 AM
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Quote:
Originally Posted by PaulK
I've found Rustoleum clogs sandpaper more quickly, so only use it when I need a white primer.
Is that the Clean Metal Primer? Or the Automobile Primer?

The former is oil based and takes a while to cure while the latter is lacquer based and dries very quickly.

From my perspective, the clean metal primer is about the same as flat paint. Anyway, because it takes a while to fully cure, it can be prone to clogging the sandpaper. I've only purchased and used it by accident (ie, due to my own ignorance ).

But I've had excellent results with their automotive primers.

Doug...not that I've painted a rocket in forever...

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  #25  
Old 11-13-2016, 03:29 PM
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Quote:
Originally Posted by Doug Sams
Is that the Clean Metal Primer? Or the Automobile Primer?

The former is oil based and takes a while to cure while the latter is lacquer based and dries very quickly.

From my perspective, the clean metal primer is about the same as flat paint. Anyway, because it takes a while to fully cure, it can be prone to clogging the sandpaper. I've only purchased and used it by accident (ie, due to my own ignorance ).

But I've had excellent results with their automotive primers.

Doug...not that I've painted a rocket in forever...

.
It used to be called auto primer, now it's called "Gray Filler Primer", #720. It's lacquer based, as it recommends lacquer thinner to clean the nozzle. The stuff dries extremely fast, I can put on multiple costs just holding the rocket for a minute between coats. Can says ready for sanding in 30m, though I usually wait a day, just so I don't bring any stink into the house.
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  #26  
Old 11-16-2016, 06:46 PM
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I said to heck with filling and sanding, I paper all my fins now. Fast, smooth and no piles of primer dust.
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  #27  
Old 11-16-2016, 07:09 PM
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Quote:
Originally Posted by Pem Tech
I said to heck with filling and sanding, I paper all my fins now. Fast, smooth and no piles of primer dust.


I've seen other people mention papering fins. Can you explain what that means? I would assume that paper sucks up paint much more so do you still prime before the top coat? But are you saying that you don't have to sand the primer before the top coat?

Thanks!
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  #28  
Old 11-17-2016, 07:25 AM
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Personally, I much prefer the finish proper filling, sanding, etc gives to fins. Papering examples I've seen look so-so in this regard. Plus, if the fin is damaged, the repair is more involved, and the resulting finish looks worse. With age papered fins look like, well, papered. By the time one makes a papered fin look as nice as a properly finished fin, about the same level of effort, perhaps more, is needed. It's an alternative, but not a great one IMO.

Allen
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  #29  
Old 11-17-2016, 07:33 AM
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On ANY rocket I have seen the "papering" technique used on fins, they always look like substandard RUBBISH.
If you want to be lazy or un-traditional and still have a nice finish, lightly sand the fins then apply iron-on R/C airplane MonoKote or Ultrakote.

I just stick with good old-fashioned Balsa Fillercoat and then Sanding Sealer for prepping ALL wood parts for topcoating. This "Dope" method works the BEST and has an olde-tyme proper nostalgic AROMA.
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  #30  
Old 11-17-2016, 08:22 AM
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The only way I've found to make papering look really nice without a lot of work is to use butcher paper, shiny side out. The primer doesn't soak in but doesn't adhere as well, so a very light scuffing is needed. Too much and the primer soaks in, not enough and even moderate stresses can cause primer to delaminate taking the finish coats with it. If primer soaks in, it often ends up bubbling the paper. Sometimes before it's finished, sometimes after the model is complete and in public view.

You still need the magic touch when gluing the paper on. Too wet and it wrinkles the paper. Too dry and it eventually bubbles or pulls away. Five or ten minutes in the sun on the pad and the balsa can outgas enough to create bubbles.

I've also soaked the entire paper fin with thin CA a couple of times. I ended up having to do a considerable amount of filling and sanding to get a nice flat slick finish, to the point that the only advantage was fin strength, not ease of finishing.
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