Sunday, April 26, 2015

Mid Power: Building the Quest Big Dog (Part 10) - Priming and Painting

Click here for Part 1

I usually use Rust-Oleum 2X gloss spray paint for my rockets. It's a decent brand, not too expensive, but with a good reputation among rocketeers.

The Big Dog is meant to be painted all white, with a red nose cone. The red should match, as closely as possible, the color of the large, wraparound decal which will go on the airframe over the white paint. That's tricky, because the decal comes on a yellow backing, so it's hard to tell what the final color will be. I had to judge from pictures online, and on the box.

Tim Van Milligan, of Apogee Components

I painted the Quad Runner gloss white and "Apple Red," and I had originally intended to use this same paint on the Big Dog.

But I stopped into a Pep Boys auto parts store, and decided to look at their paints.

A lot of people on The Rocketry Forum use an auto paint going by the name of Dupli-Color. They had this paint at the Pep Boys, and I'd heard good things about it. I picked up a can of their filler primer and two paints - Super White and Cardinal Red.

Dupli-Color is more expensive - by about 3-4 dollars a can, but I was hoping I might get a smoother, finer texture than I usually get on my paint jobs. I think I do rather well, but up close, I can see a slight texture there. I thought a special auto paint might be the solution.

Filler primer is used to fill in flaws and scratches. On rockets, it's good for filling in little spots on the airframe you didn't successfully fill with CWF (wood filler), and also for filling in small amounts of wood grain on the fins, if some is still exposed after you've worked on those. It has a "build" to it, so it fills small flaws in nicely, which can then be sanded smooth.

Usually, when I paint smaller, low power rockets, I use a little rig I built. It consists of a piece of wood with a dowel rod coming out the top, and at the end of the dowel is a used rocket motor. I just insert the motor into the rocket, and it stays upright on the stand. This works great for a standard A-C 18mm motor rocket, and if I need to paint a rocket that has a 24mm D or E motor mount, that's easy - a used 24mm D or E motor will fit right over a standard 18mm motor.

I put this rig on a lazy Susan and I can paint the whole rocket, keeping it upright and turning it as I go. As I mentioned in the Skill Level 1 Big Bertha series, you can use a rolled up newspaper as a painting wand, but then you have to figure out where to put the painting wand and rocket as the paint dries.

Using a paper wand

With this rig, I can leave everything as it is, and don't have to worry about messing up the paint job - or having the rocket fall over and getting paint on a table or the carpet.

Problem with the Big Dog is that it's much larger than any rocket I've painted so far - and it has a 29mm motor mount. I don't have any used 29mm motors, because this is my first such rocket. The rocket is a little too large for a paper wand, and any way, I wanted to let the paint dry undisturbed, without having to ram the paper wand in between some books or... whatever.

So, I went to the hardware store with my digital caliper in search of a solution. I needed... something... cylindrical, which was as close to 29mm in diameter without being any larger. I was hoping the plumbing section would offer a solution.

Turned out, it did. Turns out, a coupler for 1/2 inch PVC pipe is just over 27mm in diameter. A little masking tape would make a snug fit inside the rocket body. I found some adapters and some kind of base everything could screw into, and made a kind of wand I could either screw to a plank of wood to make a new painting stand, or simply set the wand down upright - the base is heavy enough, it won't tip over.

A 3/4 inch PVC adapter screws into the base and holds a length of 3/4 inch pipe. It is joined
via another 3/4 inch adapter to a 1/2 inch adapter, which  holds a length of 1/2 inch pipe.
Finally, at the top, is a 1/2 inch coupler. Tape goes around the coupler and the top
of the 1/2 inch adapter. The rocket slides over the coupler and the top of the adapter.
Ted Macklin pointed out to me that a 1 1/8 inch dowel is about perfect to fit into a 29mm motor mount, so that's another option for you. But with this, I didn't have to do any sawing or drilling, and I can screw down the base for heavier rockets if I need to.

I put the rocket onto the PVC stand/wand, and made sure to mask off the screw-on motor retainer - you don't want paint or primer on that, or you could have a tough time getting the retainer on and off!

Something I've recently learned about priming rockets, which I had not done before, is that it's important to lightly scuff the plastic nose cone first. For a long time, I was obsessed with making sure everything was as smooth as possible, and the nose cone was the easiest part to get perfectly smooth.

But primer works, basically, by giving the paint something to hold on to. A plastic nose cone, especially after we've sanded off the flash and filled in the divots and troughs, is very smooth. The primer itself may have a hard time holding on to that. You need to give the primer something to grip to.

I had read about scuffing the nose cone first, but I was nervous about it - wasn't I supposed to make the surface perfect first?

But I have one rocket which has suffered some chipping because of a smooth nose cone - the Estes Mini Honest John. It's got some spots where the paint and primer have completely chipped off - probably due to the nose cone colliding with the rocket body after the nose cone ejects.

You can also see here I hadn't yet learned how to fill in the low spots on the nose cone.

This isn't merely a paint chip. This is paint and primer flaking completely off!

You do this with sandpaper. You don't have to scuff the heck out of it - don't use anything too coarse. You're just giving the nose cone a little tooth - something for the primer to hold on to.

The instructions on the primer can said to use 320 grit sandpaper, which is what I did. That's still a "fine" sandpaper, but it will take the shine off. Sand the whole nose cone until it's slightly rough to the touch - and then wash off the dust.

Remember in the last post how I wrapped some tape around the shoulder of the nose cone?

Some people just put the nose right on the rocket and prime and paint away. Apparently, this is usually OK. But I've lived in enough apartments with windows painted shut, that I worry I might seal the nose cone to the rocket - then I'd have to break that seal, potentially chipping the paint in the process.

I used to pop the nose cone onto a dowel rod and prime and paint it separately. Then I'd have to find some place to put the dowel rod while the nose cone dried - usually in a cup full of pens.

Now I prime the whole thing together, and if the rocket and nose get the same color paint, I paint it this way as well.

I put the nose, wrapped in a couple layers of tape, into the airframe. Because of the thickness of the tape, it won't go all the way in - there will be a gap.

That's what I want. Then I prime - and sometimes paint - the whole thing at once. The nose cone does stick, but when I have to break the paint seal, I break it at the tape on the nose cone, not on the airframe.

Here's the whole process from an upcoming build post - the Estes Cosmic Explorer with an E-motor upgrade.

Step 1: Mask the shoulder with tape

Step 2: Put the nose cone into the rocket, leaving a gap

Step 3: Prime the rocket

Step 4: The seal breaks at the tape - not on the body
Before priming, you want to dust the rocket to remove any epoxy you sanded off the fillets, any CWF from the tube spirals and fins, and any ambient dust which has settled on the rocket. I tried a tack cloth for the first time.

Tack cloth is basically cheese cloth infused with a sticky substance.

Rocketeers have mixed feelings about tack cloth, because some feel it leaves a sticky residue on the rocket, which can effect the paint job. It certainly leaves a residue on your fingers! But if you go lightly over the rocket, it should pick up the dust, and not leave anything behind. Wash your hands before moving on.

The Dupli-Color filler primer was really nice, though it took more coats than Rust-Oleum filler primer to fully cover the rocket.

The filler primer does its job, filling in any wood grain, tube spiral - and those scuff marks you put on the nose cone. You may think, at first, that the tube spirals and wood grain haven't been properly filled in, but once you sand the primer, you should see that most of that stuff is gone, and if it isn't, another coating of primer will take care of it.

I usually do the fins first, then the rest of the rocket. Start with the trailing edges, then the tip edges and leading edges. Do each face of each fin. Then I go up to the nose cone and spray a line all the way down to the bottom, turn the rocket a little, and repeat the process, trying to overlap slightly with each pass. It's best to do light coats.

When painting, you want to avoid coats that are too heavy, because you can get a run in the paint. But if this happens with primer, don't freak out - most of the primer will be sanded off anyway.

Once the primer has fully cured, you sand everything smooth. The can I was using said you can sand after two hours, but I waited until the next day.

Using 400 grit sandpaper, I sanded the whole rocket, in little circular motions. The Dupli-Color primer didn't load up the sandpaper the way other primers have done. Sometimes, when sanding, you get a mass of primer stuck to the sandpaper - a little silvery splotch that isn't good for anything, because the abrasive is clogged in that spot.

This is what sandpaper looks like when it's been loaded up with primer. Dust from the primer gets impacted
into the abrasive surface, creating dull, silvery patches, and the paper is no longer any good for sanding.

You can extend the life of your sandpaper by occasionally brushing out the excess dust with an old tooth brush.

Once you're done sanding, before you paint, you should clean all the dust off the rocket. At this point, instead of a tack cloth, I used a piece of microfiber towel with a little rubbing alcohol. This takes off all the dust, and it evaporates quickly.

The Rust-o 2X paint is enamel. The Duplicolor is lacquer-based paint. I don't know the technical, chemical difference, but I do know that you should pick one or the other - do not mix them, or you may get weird bubbles and smearing, as the paints can react with one another.

The lacquer paint took a lot more coats to cover the rocket. In fact, by the time I was satisfied that I could no longer see through the white, I had used the whole can. The texture was fine, but nothing better than I'd gotten with Rust-o. But it was pretty.

A day later, I removed the nose cone and did the Cardinal Red top coat. The whole rocket turned out beautiful. After the red dried, I put the rocket together to take a look.

The rocket is nearly done. Just a few more steps to go.

Click here for Part 11

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  1. Very nice! Yeah, it always sucks, using up a can of paint (adds to the rocket’s cost), but when it looks pretty, it all seems worth it.

    My understanding with lacquers is that you can put other stuff *on top* of lacquer paints, but you shouldn’t put the lacquer on top of anything else (so you can use a lacquer sanding sealer on the base…).