New Technique - Glossy Surface on Fiberglass

For any of you have fiberglassed your own tubes, one of the things that you are typically left with is a rough surface.

At that point you have two choices: sand it down (and weaken the structure you just created) or begin the fill-sand-repeat routine.

But I tried a new method to see if it would work (at least for me). I have done rocketry enough to know about 50% of the time my ideas actually work in the real world, so I don't get my hopes up too much when I try something new.

It is actually an old idea, but implemented at a different idea. It's taking polyester film (i.e., Mylar) and wrapping it around the airframe with a wet layer of epoxy.

I had two 2.60" OD airframe sections I wanted to cover, one was 8" and the other 7". I cut two pieces of polyester film so that there was about a 1/4" of overlap when wrapped. I did not treat either film with any kind of mold release.

So I mixed up a batch of Aeropoxy laminating adhesive with 2-hour hardener. After the initial mix, I added a lot of microballoons (I wanted it lightweight) and a smaller bit of milled fiber for structure to the epoxy. I cleaned off the surface of the airframe with acetone to remove any grease to help with adhesion. I then applied the epoxy slurry to the surface of the airframe with a chip brush.

After "painting" the entire airframe I wrapped the film around it. The method was to gather it at the middle and firmly apply pressure, then tape with blue tape. Then work your way out to the edges, taping each new section as you go. After taping it up, I removed the excess epoxy and set it aside to cure.

I like to give Aeropoxy at least 2 days to cure.

Tonight I took the tape off, and here is the result:



The two tubes on the outside have been treated, whereas the center one is just plain fiberglass.

All in all, I am quite pleased with the results.

BTW, I think I got these tubes from Uncle Mike's.

Greg

Although they do look nice, I might have still prefer peel ply over mylar.
Mylar is non-pourus so once it's placed, epoxy cant flow in or out of it. This means that (unlike peel ply) air bubbles will be hard to work out and excess epoxy wont be able to leak out.

It does look very interesting though. You might be onto something.
Do you think you could poke holes in the Mylar to get epoxy to flow in and out?

Also where do you get your Mylar and what thickness was used?

Alex

Interesting. What's the weight of the tubes, treated with the mylar described above, vs FG/ peel ply?


Later!

--Coop

Aksrockets said:

Although they do look nice, I might have still prefer peel ply over mylar.
Mylar is non-pourus so once it's placed, epoxy cant flow in or out of it. This means that (unlike peel ply) air bubbles will be hard to work out and excess epoxy wont be able to leak out...

Click to expand...

Working the way I did, I had no air bubbles. Not a one.

Aksrockets said:

... It does look very interesting though. You might be onto something.
Do you think you could poke holes in the Mylar to get epoxy to flow in and out? ...

Click to expand...

The film is thin enough to poke a small hole in to bleed some out. But you wouldn't be able to put it back in though.

Aksrockets said:

... Also where do you get your Mylar and what thickness was used?

Alex

Click to expand...

I got it a long time ago, but the tube that it came in says www.Stencilease.com. I wrote in marker on the tube 0.014" for the thickness.

With a longer tube or a larger diameter, I might go with something a tad thicker.

Coop said:

Interesting. What's the weight of the tubes, treated with the mylar described above, vs FG/ peel ply?


Later!

--Coop

Click to expand...

The un-fiberglassed tube weighed about 36 grams (15" length).

A length (15") of fiberglassed tube (no peel ply) weighed in at 86.6 grams. The two sections (8" & 7") of glossy tubes weighed 94.1 grams, so a delta of 7.5 grams to get the high gloss finish. I think that's pretty good.

The whole purpose of getting a gloss finish is that I wanted the surface to be ready for Trim Monokote, which sticks best to a nice, flat, uniform surface. And that is what I have. :smile:

Greg

I've had good success getting a smooth surface when vacuum bagging by using perforated release film. No additional layer of epoxy was needed, and only a light sanding was required to remove the "nubs" left behind.

I didn't want to go through the hassle of vac bagging the airframe. I'm already getting less than 50% for the epoxy/cloth ratio (which is pretty good for hand layups). Even though it's an extra step beyond the initial layup, it's not that hard or time consuming to do, plus I really don't have to do anything to the surface to go to the next step. Perhaps I have some release film around though, I'd have to check.

BTW, this airframe for this rocket is for my youngest child. I wanted something robust enough to deal with the tough landing environment that we have where I fly (concrete and asphalt on the hard side). When finished, I hope it will be able to fly on D12's on the low side, up to a Pro24 3G for the high side.

Greg

tonka said:

I've had good success getting a smooth surface when vacuum bagging by using perforated release film. No additional layer of epoxy was needed, and only a light sanding was required to remove the "nubs" left behind.

Click to expand...

Was this on a tube, or on a flat plate?

When I've attempted vacuum bagged tubes using anything but peel ply pulled REALLY REALLY tight, it forms giant longitudinal wrinkles that ruin the strength.

I've done it on both tubes & individual fins. I've found that anytime I get longitudinal wrinkles on tubes is when the base layers weren't pulled tight before wrapping with the release material, or the fiberglass/carbon/kevlar was way over-saturated with resin before lay-up.

Last night I did another section of airframe (2.60" OD, ~7" length). This time I weighed it before the epoxy "gloss coat" was applied. One observation this go 'round was that the epoxy was a little more runny than I remembered from the first time. So I stopped and added more microballoons and milled fiber to get it more toward the consistency of what I remember. But what I should perhaps do is be a little more disciplined and weigh out the amendments before hand, so I am not reduced to "a pinch of this and a dash of that".

Also, the I was a little more disciplined in the application of the blue tape binding wrap. I did my first binding in the middle. Then did a shallow "barber pole" wrap from the middle going to one end, which bled out the excess with each successive wrap. Then started at the middle again, and did the same thing going to the opposite end.

Greg

Maybe it's because it;s almost 2AM, or maybe I just don't get it. You loose me with the wrapping of the mylar and then the tape. I can't picture the process in my head. If you could post pics next time, that would be great, or maybe I'll just catch you at a launch and we'll talk about it.

The next time I do the wrap, I can have one of my children take some pics. But until then, I'll try to describe it again.

What I do is cut the film to shape, which is usually rectangular and I try to get it with 90 degree angles at each corner. I think the last one I did measured about 7.5" x 8.5". After coating with epoxy, I wrap the film around so that it completely surrounds the airframe with a little overlap on the open ends and the longitudinal seam. I take one strip of tape and basically make it like a belt and cinch the middle of the airframe. Then I do the shallow "barber pole" from the center of the belt, to one of the open ends. Then I repeat the process with the other open end.

I hope that makes a little more sense.

Greg

ok, so the belt stays at the middle and then a piece of tape is spiraled to each end? I am guessing that the spirals would overlap in order to work the excess epoxy out of the ends?

I'll have to play with some tubes & mylar when I get home. I don't understand things abstract, I have to see/touch/taste/feel my way through...

I might try this with parchment paper in the near future. In theory, it'll work the same way. I wont be doing the tape wrap method until I get a good outcome.
The appeal of parchment paper is the avalibility and price. Just about anyone can go down to the grocery store and pick up a big ole thing of parchment paper for a few bucks.

I'll post the results on this thread if you guys are interested.

Alex

You got it T-Rex! Like you said, you do an overlapping spiral from the central "belt", and the epoxy bleeds out as you work to the ends.

I'm the same way. I have to learn by doing it.

Greg

Aksrockets said:

I might try this with parchment paper in the near future. In theory, it'll work the same way. I wont be doing the tape wrap method until I get a good outcome.
The appeal of parchment paper is the avalibility and price. Just about anyone can go down to the grocery store and pick up a big ole thing of parchment paper for a few bucks.

I'll post the results on this thread if you guys are interested.

Alex

Click to expand...

I do use parchment paper as a surface release for epoxy, but mostly with flat stock like fins. For this same rocket, I put 2 layers of ~6 oz. FG on each side of the balsa core, and put it between two glass panes (glued to MDF) with the parchment paper between the glass and layup. Then I put a weight on top and let it cure. The fins come out nice and planer, with a fairly good surface, too.

I don't know how well it would work on a tube, since 14 mil film has properties that make it want to bend in one direction at at time, whereas paper can be wrinkled fairly easily if it is taped. You can try it with and without taping, and see how it goes and report back.

Greg

I did another epoxy glossy coat, and did a before and after weigh in of the airframe.



So the "before" is 40.9 grams.



The "after" turned out to be 45.7 grams, so a delta of 4.8 grams (less than the average weight of a nickel). Perhaps a high-build primer might weigh a little more. But without a test it's hard to know. I do know I didn't need to sand!

Greg

Here is a pic of one of the tubes with Trim MonoKote applied.



Greg

Ooooooooh shiny!! I will definitely have to attempt this when I decide it is time to wrap tubes. Thanx for sharing!!!!!

I finally finished it!





Greg

This thread reminded me that on the maiden flight some time ago, I flew it on a motor that I thought was adequate but was WAY underpowered.

As soon as it struggled into sky I knew it was in trouble, and after the anemic apogee it nosed over and came in ballistic, slamming hard into the asphalt.

The nose cone shattered and drove what remained of it a couple of inches or so into the airframe.

I cut off the end and put another section of FG airframe on it and gave it a new nose cone and all was good. Had that not been a FG'd airframe I maybe could have salvaged just the fin can. So I am glad I took the extra time to fiberglass it as it has had nothing but successful flights beyond the first one.

Greg

Attached is the OpenRocket file.

Greg

View attachment FireStarGL.18.Basic.ork