Questions about fiberglass imperfections

[cthunter01]

Hi guys!

So I finally decided to stop worrying about messing up some cardboard tubes with fiberglass and just dive in and try glassing some tubes. Best case I learn a new skill and get super smooth tubes, worst case I just learn a new skill and get the opportunity to try again...

I think they turned out okay actually. There are some imperfections I'm hoping to get some advice on, but overall I think they're decent for a first try.

So I got some soller composite sleeves (6"/light, 9.5 oz), 7.6" composite heat shrink tubing, and West System 105/206 epoxy. Well I already had the epoxy because I like constructing with it along with some 406 silica thickener. But the fiberglass and heat shrink is new. The tubes are 5.5" LOC cardboard.

I tried glassing two tubes, each in a slightly different way.

For the first one: I put the sleeve over the cardboard tube dry, mixed up enough resin and hardener so I wouldn't have to stop mid-work to make some more, then applied the epoxy. I wetted it thoroughly enough to make sure the fiberglass was completely transparent, then slid the heat shrink tubing over the tube. After trying to shrink it with a heat gun, it didn't quite shrink tightly over the tube. I thought I sized the right shrink tubing (I did size it correctly, but this was my first attempt and I got scared that it would ruin the finish so I cut it off). I took some more shrink tubing, split it to make a sheet, then just wrapped the tube as if it was a mylar sheet.
After waiting about 8 hours or so, I peeled the wrap and was pretty pleased. It does, however, have some "dry" spots that will need filling (I think?) I'm a little unsure how there are so many, as it was wetted to the point of transparency before I wrapped it with the shrink wrap. Though, I think I might have squeegeed out too much epoxy after wrapping it. And the cardboard may have soaked up more than I anticipated or realized. It's still as solid as a rock, but it's rough in areas. Picture below:

So, what to do with the rough areas? I did a little research and came up with using epoxy w/ microballoon filler. Just apply that to the tube and wipe it smooth. Then I *should* have a sandable surface once it cures, and I can sand it smooth. Or should I do something else to fill the rough areas?

The second tube: This is a smaller one. Based on the outcome of the previous tube, I left more epoxy on the tube after wrapping it with the shrink wrap. Also this time, I tried the shrink tube again and just gave it more time and more heat and it did eventually tightly shrink over the tube. *However*, it left some wrinkles near the edges of the tube. Possibly or probably because I erred on the side of leaving too much epoxy in place, whereas before I didn't leave enough. So after removing the shrink tubing (6 hours later), those wrinkles left wrinkles in the epoxy. The fiberglass is still tightly bound to the cardboard and smooth as near as I can tell, but the resin is wrinkly in some areas. Also, there's still some "dry" spots, but far less than before. Picture below (red circles show wrinkles in resin, green is a dry area):


My next question is: what am I going to do with those wrinkles? I suppose I just sand them down, but does anyone else ever get them? They're pretty small, but not nothing. I couldn't get rid of them while applying heat and shrinking the tubing, so they cured that way. I'm thinking I might just avoid using shrink tubing in the future. Anyone else have success with shrink wrap and fiberglassing cardboard tubes?

 

[cthunter01]

I scaled the image sizes way down so they load fast for people that might not have fast internet connections. But it reduced the quality by quite a lot. I can upload higher res pictures if those aren't clear

 

[hobie1dog]

I suggest abandoning all the extensive labor and frustration, and still ending up something that's not smooth?... why don't you just start using fiberglass tubing? it's as smooth as a baby's butt, with no work involved at all.

 

[tfish]

@cthunter01

For your first glass job it looks much better then my first one!

Don't worry about what other people say...some of us like building and learning things.

I would sand down the high points, fill the low areas paint it and fly the hell out of it.

Build another and keep learning, flying and having fun.

Tony

 

[cthunter01]

I suggest abandoning all the extensive labor and frustration, and still ending up something that's not smooth?... why don't you just start using fiberglass tubing? it's as smooth as a baby's butt, with no work involved at all.

Haha, why indeed! I have some smaller fiberglass rockets that came that way, but I wanted to see about building something larger that’s also strong yet a lot lighter than solid fiberglass would be.

Plus I would like to learn more about it. Maybe the biggest reason to do it was how I was kind of afraid of doing it for fear of making mistakes. And not doing something because I’m afraid it’ll be hard doesn’t sit well with me.

 

[hobie1dog]

John Coker weight chart:

Common Name	Manufacturer	Material	Weight¹	Thickness	Grooves
cardboard	Loc/Precision	paper	103	0.060"	light
phenolic	Public Missiles, Ltd.	paper phenolic	143	0.069"	medium
flexible phenolic	Giant Leap Rocketry	paper phenolic	149	0.067"	medium
Blue Tube 2.0	Always Ready Rocketry	vulcanized paper phenolic	174	0.060"	light
MagnaFrame	Giant Leap Rocketry	vulcanized paper phenolic	174	0.067"	heavy
canvas phenolic	MAC Performance	cotton phenolic	185	0.060"²	none
seamless phenolic	Black Cat	phenolic	182	0.063	none
fiberglass	Performance Rocketry	filament wound FG	248	0.063"	none
carbon fiber		filament wound	163	0.045"	none

¹ The units here are grams per foot (yes, tha

 

[Grog6]

I'd add epoxy to the dry areas and anywhere else that needs it, and give it some time on the pump.

 

[hobie1dog]

I know it's been done on here before, but too hard to search for, is how much weight you end up with by taking cardboard tubing and adding fiberglass to it then all the resin.

 

[cthunter01]

Maybe “ a lot lighter” is an overstatement. But my 2.6” all-fiberglass rockets are chonkers. Relative to similarly sized cardboard rockets anyway. I just suspect wrapping cardboard with a single fiberglass layer and laminating it would be lighter than all fiberglass, but I don’t know that for sure. It’s all a learning experience for me. and actually, I quite enjoyed painting on that fiberglass surprisingly enough. Very satisfying actually! hopefully next time it’ll be both enjoyable and a great smooth outcome.

I’ll come back and update this thread after I try smoothing the tubes, and report how that goes.