Help Me Fix My L1 Disaster

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lowga

lowga

A.K.A. 'Mr. HoJo'
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Can you tell that I hadn't built a rocket in 25 years and never before with epoxy? The fins on this Madcow Cowabunga are straight, but the fillets look like a five year old built this thing.

Despite that, it flew straight and true--and is otherwise a nice rocket. The nose cone was modified to accept electronics and a mounted camera shroud allows for great in-flight videos. I'd love to fly it more, but I'm embarrassed to take it to launches.

Refinishing the paint is easy enough. Got it sanded down and primer on...but I have no idea about how to repair the fillets.

Is it possible to remove the epoxy? Or do I need to sand them down by hand--tried that for about 45 minutes, but couldn't make much of a dent. Got worried about the damage to the plywood fins in the effort so decided to stop and seek assistance.

Since building this one, I've built a dozen more mid- and high power rockets and gotten a good hang of fillets. I'd love to remove these and make my L1 bird something I'd be proud to take the park. Any ideas on how to fix this "fillet disaster?"

All help appreciated.
 

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For me, fillets are the worst part of building rockets. Mine never look good. I’m always stuck sanding them and filling them. I like the Aeropoxy light for covering mistakes and finishing fillets. It does nothing for strength but it makes them more prepared for paint.
 
My recommendation would be to get a wooden dowel that is about the same size of the fillets with 180 grit sandpaper and sand the fillets to get a better radiused fillet.

It will take a lot of time, so be patient with it. Do not rush it or it will come out worse.
 
As per what tsmith said for the correction, and definitely lots of patience.

Masking and dowels for the next build. I like the use two different size dowels. The first one bashes everything roughly into shape, and the final smaller diameter gives the finished radius. As others have said, metho to keep it clean and slippery.

If you add something like microballoons to the fillets next time they will be much easier to sand. That's what I use.
 
I guess it’s possible to reshape hardened epoxy fIllets by hand sanding. A lot of careful hand sanding. A lot. I think your best bet is to fill the low spots and ridges with your goop of choice and call it good.
 
samb said:
I guess it’s possible to reshape hardened epoxy fIllets by hand sanding. A lot of careful hand sanding. A lot. I think your best bet is to fill the low spots and ridges with your goop of choice and call it good.
Click to expand...
Yup, if they bother you, building them up a bit to even them out is way easier than trying to sand through cured epoxy.
 
I wear nitrile gloves. Not everyone becomes sensitized to epoxy, but if you do it will change the hobby for you and possibly even ruin it for you. It’s the sensible thing to do.
I use either a tongue depressor or a glove tip dipped in alcohol to smooth fillets. Using tape makes it easier to keep the edges straight and uniform.
It looks like the main problem was getting enough epoxy down to fill the joint. Try doing shorter fin joints first. The choice of epoxy and possibly filler makes a huge difference too. You need an epoxy that cures slowly. You also have to keep it from cooking off, which is an out of control exothermic chain reaction where the heat given off by the reaction causes the epoxy to react even faster which causes even more heat until that cup of epoxy you have mixed up literally melts through the plastic cup you mistakenly used and drops onto your feet and floor.
To answer your question, I would not attempt to sand that fillet. You’ll end up dishing the fins and body tube much faster than the epoxy. Instead I would either cut it out with a hot chisel, Dremel cutoff disk, or multitool or I would put a larger fillet over it.
 
Might I be a voice of dissent on this endeavour?

Don't worry about it making a trophy. This is a milestone in your journey, and no matter how it looks that rocket will always matter. Right now you might want to re-do it, but that patina will never come back. If you stick with the hobby long enough you WILL reach a point that you wish you never refinished it. Them wavy fillets have history behind them.... keep 'em. Be proud of the rocket for what it represents.

I'd wager a bet that if you built another Cowabunga and made it absolutely perfect that the old one would still be your favorite.

-Hans
 
IMO it's the paint/dirt that make it look bad (no offense intended). Fillets are good enough. Clean it up and spray paint it if the appearance bothers you, and then move on to the next project, having learned a few things from this project and this thread.
 
n27sb said:
I agree with Steve here. Nice big fat fillets on those big fat fins would look great.
Click to expand...
The easiest way to cover those fillets would be with 2-part lightweight body filler. The last time I bought an entire gallon it only cost $11. It’s probably $18 by now. Mix it up, trowel it on with a cake decorating knife or tongue depressor as smooth as you can, give it 10 minutes, and then sand it smooth. It sands easy. The experience will also help you learn the techniques for epoxy fillets. There will be those who say body filler doesn’t stick well to epoxy. That may be true; it certainly doesn’t cross-link, but it hasn’t cracked loose on the large rocket where I’ve used it. It’s cosmetic only.
Or do as Hans says and fly it the way it is. Everyone started somewhere and there’s nothing to feel ashamed of in flying your rocket.
 
Good advice all around. I've moved on to using masking tape, and fondant tools to get much smoother fillets on my rockets now.

A few months ago, I found a vintage Estates Patriot at a yard sale. It looked like it was built in the 1980's or early 90's. Painted bright pink with a lot of "patina." I thought about refinishing it, but was advised to leave it as is and just enjoy flying it.

I took that advice--and was surprised by the reactions at the field. Many of us old-timers seemed to enjoy seeing a vintage rocket.

I'm going to give some thought to either making the fillets larger or simply repainting the rocket and flying it as is. As you say, the rocket has a history--and I need to honor that.

Grateful for the advice.
 
Steve Shannon said:
I wear nitrile gloves. Not everyone becomes sensitized to epoxy, but if you do it will change the hobby for you and possibly even ruin it for you. It’s the sensible thing to do.
I use either a tongue depressor or a glove tip dipped in alcohol to smooth fillets. Using tape makes it easier to keep the edges straight and uniform.
It looks like the main problem was getting enough epoxy down to fill the joint. Try doing shorter fin joints first. The choice of epoxy and possibly filler makes a huge difference too. You need an epoxy that cures slowly. You also have to keep it from cooking off, which is an out of control exothermic chain reaction where the heat given off by the reaction causes the epoxy to react even faster which causes even more heat until that cup of epoxy you have mixed up literally melts through the plastic cup you mistakenly used and drops onto your feet and floor.
To answer your question, I would not attempt to sand that fillet. You’ll end up dishing the fins and body tube much faster than the epoxy. Instead I would either cut it out with a hot chisel, Dremel cutoff disk, or multitool or I would put a larger fillet over it.
Click to expand...
Steve what are some of the signs of getting sensitized to epoxy? I need to be more carefull?
 
REK said:
My recommendation would be to get a wooden dowel that is about the same size of the fillets with 180 grit sandpaper and sand the fillets to get a better radiused fillet.

It will take a lot of time, so be patient with it. Do not rush it or it will come out worse.
Click to expand...
SAme idea, but I'd start with 100 grit paper--will sand down faster. Once you get close switch to finer sandpaper. Another option: start with a metal round file and snad down most of the way before switching to sandpaper.
 
If it's a good flier then it's not broke so don't fix it. You can always reserve it to fly in less than optimal conditions when you don't want to risk losing one of your better rockets or if you have a motor that you're uncertain of its reliability but you don't want to waste it.
 
crossfire said:
I guess I am saying what are the symptoms
Click to expand...

From the first paragraph of the link that Steve posted:
"Perhaps the most common sign of epoxy sensitisation occurs on the skin via rashes, however irritation to the eyes, nose, throat and lungs can also occur. "
 
And I agree with the thought of "just leave it alone". Reworking it to meet your current workmanship standards is kinda like revising history - I didn't like my sixth grade school picture, so I'm gonna try to look six again and dress the way I think I should have looked. Flying your rocket as it is, is also a way to connect to less experienced rocketeers - "Yep, some of my early builds weren't very good either - this is my L1 rocket - but I've gotten better".
 
Filler/Bondo... sand... repeat. Make the radius larger and fill in the lows. It’s not a hotrod so no one will be kicking the tires and checking the panels with a magnet! ;-)
 
Steve Shannon said:
https://www.epoxyschool.com/blog/health-and-safety-epoxy-sensitisation/
Also, once you are sensitized, you’re always sensitised.
Click to expand...
Back in the 90s, Dave Gawlik, aka "Dangerous Dave," developed a sensitivity to epoxy/hardener. A single small spot on his bare skin would cause all sorts of rashes, etc. Dave did composites. Lots of fiberglass, carbon fiber, Kevlar, etc. So, this sensitivity caused Dave no end of problems. He had to bundle up in long-sleeved shirts, wear gloves, a respirator, etc. just to work, as he was making lots of composite parts for rocketry at the time. Not too bad when it was the winter, but when Dave was working out of a storage unit in Athens, GA in the middle of the summer, it was downright ugly.

Take care of yourself, always use protective layers and do your best to minimize contact with epoxy, hardeners, etc.
 

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