Help Fixing Ugly Fillets

lowga

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Don't laugh. Below is my first ever high-power rocket that I built for level 1 certification. It started life as a Madcow Cowabunga kit, and I modified it into a telemetry and video platform. The nose cone has a large compartment for telemetry/GPS and I added a Mobius camera shroud for video.

Obviously, I knew nothing about making fin fillets and had never worked with epoxy before.

While it flew straight and true, it looks awful. I've improved since then, but I would like to save this rocket for sentimental reasons. I tried sanding the fillets to remove them, but no joy. The epoxy is hard as cement. Even the Dremel tool couldn't make a dent. I have considered making larger fillets over top of them. But not sure if that will work.

If you can stop laughing and pointing long enough, I'd love some suggestions. Grateful for the wisdom of more experienced rocketeers.
 

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FMarvinS

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Hi,
If you didn't try the grinder bit with your dremel, then give it a try. If you go to the middle of the you tube video below, a cracked fillet is removed for replacement with a new fillet. The displayed technique should be applicable. Also, once the old fillets are removed, you can follow the advice of fillet setting demonstrated in Crazy Jim's thread on building a Wildman Dark Star as organized and posted by "mellow yellow" found in the permanent threads at the top of the high power rocketry section above. Good Luck!
Fred, L2
 

FlyBy01

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Don't laugh. Below is my first ever high-power rocket that I built for level 1 certification. It started life as a Madcow Cowabunga kit, and I modified it into a telemetry and video platform. The nose cone has a large compartment for telemetry/GPS and I added a Mobius camera shroud for video.

Obviously, I knew nothing about making fin fillets and had never worked with epoxy before.

While it flew straight and true, it looks awful. I've improved since then, but I would like to save this rocket for sentimental reasons. I tried sanding the fillets to remove them, but no joy. The epoxy is hard as cement. Even the Dremel tool couldn't make a dent. I have considered making larger fillets over top of them. But not sure if that will work.

If you can stop laughing and pointing long enough, I'd love some suggestions. Grateful for the wisdom of more experienced rocketeers.
We are all here to learn so let's start with what kind of epoxy are you using?
 

mtnmanak

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Since this is a carboard tube, I would recommend against the power tool options. You can use a dremel or palm sander, but you will probably end up going through the tube before you get the fillets clean.

60 or 80 grit wrapped around a dowel can be surprisingly aggressive. I have sanded down RocketPoxy fillets many times using that method. Go slow, try not to hit the cardboard and a little elbow grease.

In the photos below, I used West Systems epoxy mixed with chopped carbon fiber (to add flexibility). This was on an 8" diameter Goblin. When cured, that mix is as hard as metal. 80 grit on a Durablock and then around a dowel took the fillets down nicely. They were finished with Bondo, sanded smooth with fine grit and painted. Point is, hand sanding can take down epoxy pretty well.

Getting paint drips between the fins, on the other hand... Ugh.

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FlyBy01

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It was RocketPoxy. I used way, way too much.
I tape off the fins except for where you are epoxing. Wearing gloves use either a piece of PVC pipe or a socket dipped in isopropyl alcohol to draw the excess epoxy. As the epoxy sets you can smooth things out with your gloved finger dipped in alcohol.
 

StreuB1

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Dowel rod of a suitable diameter wrapped with 3M (Purple) 60 grit paper will make quick work of those fillets. A 6" flat durablock (Amazon) and the same 60 grit will knock down flat areas adjacent to the fillets. Then move to 120 grit to smooth things out. You can clean that all up in an hour or so, no problem.
 

SkyFire

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Don't laugh. Below is my first ever high-power rocket that I built for level 1 certification. It started life as a Madcow Cowabunga kit, and I modified it into a telemetry and video platform. The nose cone has a large compartment for telemetry/GPS and I added a Mobius camera shroud for video.

Obviously, I knew nothing about making fin fillets and had never worked with epoxy before.

While it flew straight and true, it looks awful. I've improved since then, but I would like to save this rocket for sentimental reasons. I tried sanding the fillets to remove them, but no joy. The epoxy is hard as cement. Even the Dremel tool couldn't make a dent. I have considered making larger fillets over top of them. But not sure if that will work.

If you can stop laughing and pointing long enough, I'd love some suggestions. Grateful for the wisdom of more experienced rocketeers.
Laughing.gif
 

StreuB1

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Since this is a carboard tube, I would recommend against the power tool options. You can use a dremel or palm sander, but you will probably end up going through the tube before you get the fillets clean.

60 or 80 grit wrapped around a dowel can be surprisingly aggressive. I have sanded down RocketPoxy fillets many times using that method. Go slow, try not to hit the cardboard and a little elbow grease.

In the photos below, I used West Systems epoxy mixed with chopped carbon fiber (to add flexibility). This was on an 8" diameter Goblin. When cured, that mix is as hard as metal. 80 grit on a Durablock and then around a dowel took the fillets down nicely. They were finished with Bondo, sanded smooth with fine grit and painted. Point is, hand sanding can take down epoxy pretty well.

Getting paint drips between the fins, on the other hand... Ugh.

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This is literally my Friday and my weekend right now LOL

Doing the Demon 150 at the moment and then need to gouge out the fillets an a 5" Jart with a burr and lay new fillets as the old ones are cracked.

Hate doing this stuff but the results.....well, it drives the work. :)
 

mtnmanak

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This is literally my Friday and my weekend right now LOL

Doing the Demon 150 at the moment and then need to gouge out the fillets an a 5" Jart with a burr and lay new fillets as the old ones are cracked.

Hate doing this stuff but the results.....well, it drives the work. :)

Good luck on that sanding! I hand sanded the Goblin because I didn't want to mess up those stupendously expensive carbon fiber fins. When the whole thing is FG and it is a "big" rocket, I pull out the random orbital sander, load up some 60 and 80 grit discs and go to town.

On big rockets/fillets I switched to the West with chopped carbon fiber and haven't had a cracked fillet yet. I still use RocketPoxy on 4" and below birds, but the chopped CF adds some flexibility to the fillet for the big guys.

When you mix in the CF, you get a thick mixture that has the consistency of wet hair:

PXL_20220416_105447230.jpg
 

danisman

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There are so many epoxy products out there. What do you like about West Systems in particular? Also, which West epoxy product do you prefer?
 

Woody's Workshop

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I find those cheap diamond dust bits for the Dremel come in very handy.
I get some of the 30 bits kits off ebay for $5-$7, but you never know what grit your getting unless you pay more.
For specific things I'm doing I buy different sized ball tips off Amazon where you get 20-30 bits for about $10 and pick the grit and size you want.
If it was me I'd knock off the ugly high spots and globs and put another coat over top.
Using a tongue depressor or pop sickle stick to smooth it out before it sets up.
If it's just for looks and strength is already there, you can try some kind of filler instead of epoxy.
It would be easier to sand than epoxy.
 

mtnmanak

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There are so many epoxy products out there. What do you like about West Systems in particular? Also, which West epoxy product do you prefer?

Don't want to turn this into an epoxy thread, but for this particular application, West provides a high strength epoxy at a low viscosity that mixes perfectly with the chopped carbon fiber to get the consistency I was looking for. Thicker epoxies are too viscous and, when you mix in the CF, it is like trying to apply wet playdoh.

I do switch epoxies to fit the application, but I go through a lot of West 105/205. It is definitely the epoxy I use the most.

Some reasons:
- Can dial in the cure time by changing which hardener you use
- Cures fine at room temp
- Can dial in the viscosity using fillers from a light weight oil consistency to something like peanut butter
- Easy to obtain - can get it on Amazon or from most of the rocket vendors
- Easy to inject with a syringe
 
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cwbullet

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Don't laugh. Below is my first ever high-power rocket that I built for level 1 certification. It started life as a Madcow Cowabunga kit, and I modified it into a telemetry and video platform. The nose cone has a large compartment for telemetry/GPS and I added a Mobius camera shroud for video.

Obviously, I knew nothing about making fin fillets and had never worked with epoxy before.

While it flew straight and true, it looks awful. I've improved since then, but I would like to save this rocket for sentimental reasons. I tried sanding the fillets to remove them, but no joy. The epoxy is hard as cement. Even the Dremel tool couldn't make a dent. I have considered making larger fillets over top of them. But not sure if that will work.

If you can stop laughing and pointing long enough, I'd love some suggestions. Grateful for the wisdom of more experienced rocketeers.

Sanding is the only fix I can think of. Enough black powder can help you set it up for a rebuild.
 
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David Schwantz

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Fillets on a Wildman Mach2. Taped off fin and body tube to width I want fillet to be. Used Pro Line epoxy. Applied with a syringe then pulled the fillet with my finger. pull off tape.
On your fillets, I would grind them down, not off. Then bondo over them and sand to shape. Do not use bondo in a tube as it shrinks when it dries. i also like to use dowels, and fingers, and sanding blocks and mouse sander.
 

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Be careful with all of the Bondo products as you will notice on the tube that it says warning: Eye Irritation, and they mean it, as I ended up in the Urgent Care and had my eyes have swollen 1/2 shut, Feeling like somebody had thrown sand in my eyes because of having the vapors come up in my eyes. I now use a respirator and safety goggles and have a fan blowing across so that it takes the fumes away before it comes up into my face.
 

neil_w

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Don't laugh. Below is my first ever high-power rocket that I built for level 1 certification. It started life as a Madcow Cowabunga kit, and I modified it into a telemetry and video platform. The nose cone has a large compartment for telemetry/GPS and I added a Mobius camera shroud for video.

Obviously, I knew nothing about making fin fillets and had never worked with epoxy before.

While it flew straight and true, it looks awful. I've improved since then, but I would like to save this rocket for sentimental reasons. I tried sanding the fillets to remove them, but no joy. The epoxy is hard as cement. Even the Dremel tool couldn't make a dent. I have considered making larger fillets over top of them. But not sure if that will work.

If you can stop laughing and pointing long enough, I'd love some suggestions. Grateful for the wisdom of more experienced rocketeers.
This may not be helpful but I think there's something to be said for preserving it as-is. Focus on making your *new* rockets pretty. I confess I have no interest in going back and fixing mistakes on old rockets, just trying not to repeat the same mistakes on new ones.

Of course, if you really want to fix those fillets then go for it.
 

loopy

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If they are strong enough and working fine from that perspective, just get some Bondo spot putty and a plastic spoon. Tape off where you want the edges of the fillets to be. Spooge a bead of spot putty on the existing fillet, then pull the spoon through to smooth it out. Pull the tape, then sand smooth when dry.

For future rockets, do this exact routine, but with the epoxy instead of spot putty.
 

lowga

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Not yet. Still considering my options. Plan to purchase a couple of wooden dowels, and attempt wrapping them in sandpaper before trying the Bondo fix. I can see where Bondo might work--but the fillets would be very large. I think the rocket would be more attractive if I can sand them down, and then redo fillets with epoxy.

Marty--if you have other advice, or if others have input I'm all ears. Will probably work on it this weekend.
 

Chris_H

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Aeropoxy laminating epoxy, mixed with some colloidal silica and some high density adhesive filler, makes great fillets. Enough of the colloidal silica and also the high density filler, that it has plenty of 'hang' to do all three or four sets at once. Pull with whatever your pulling tool is, at a high angle, first, to start to get the fillet, then a finish pass at a lower angle to leave a gorgeous fillet. The carbon fiber addition cat hair mess caused issues for me when pulling, too much solvent needed to keep things flowing. And, I read, that the amount of carbon fibers needed to really make a difference in the strength of the fillet, is quite high. I needed solvent for okay pulls with my CF fillet mix. Maybe with a very high CF mix, and using some release fabric and a mold, that might be great. If I were going for absolute maximum strength, this is probably what I would do. I think many people with good intentions, try the exotic materials, but their technique is not fully developed. The mix I mentioned above, no solvents necessary. I do not like rocketpoxy, no need for it. I have used it. If you like it, great. It is probably great stuff for some people. Not me. Aeropoxy laminating resin plus high density adhesive filler and colloidal silica, this is the easiest fillets I have done. Apply, pull, rotate and do the next set. Do the whole rocket. Make sure there is enough colloidal silica and adhesive filler so that it 'hangs' until curing, without moving.

West is good. Raka is good. Aeropoxy is better.
 

Chris_H

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For cleaning up ugly fillets, grind them down however you see fit, into freshly abraded old fillet, just below the new finished radius, and all of it abraded, and then use the method I mentioned above. Or, whatever else feels right for you. Continuing learning is the path...
 

thzero

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Aeropoxy laminating epoxy, mixed with some colloidal silica and some high density adhesive filler, makes great fillets. Enough of the colloidal silica and also the high density filler, that it has plenty of 'hang' to do all three or four sets at once. Pull with whatever your pulling tool is, at a high angle, first, to start to get the fillet, then a finish pass at a lower angle to leave a gorgeous fillet. The carbon fiber addition cat hair mess caused issues for me when pulling, too much solvent needed to keep things flowing. And, I read, that the amount of carbon fibers needed to really make a difference in the strength of the fillet, is quite high. I needed solvent for okay pulls with my CF fillet mix. Maybe with a very high CF mix, and using some release fabric and a mold, that might be great. If I were going for absolute maximum strength, this is probably what I would do. I think many people with good intentions, try the exotic materials, but their technique is not fully developed. The mix I mentioned above, no solvents necessary. I do not like rocketpoxy, no need for it. I have used it. If you like it, great. It is probably great stuff for some people. Not me. Aeropoxy laminating resin plus high density adhesive filler and colloidal silica, this is the easiest fillets I have done. Apply, pull, rotate and do the next set. Do the whole rocket. Make sure there is enough colloidal silica and adhesive filler so that it 'hangs' until curing, without moving.

West is good. Raka is good. Aeropoxy is better.
Or just rocket poxy.
 

cautery

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Don't laugh. Below is my first ever high-power rocket that I built for level 1 certification. It started life as a Madcow Cowabunga kit, and I modified it into a telemetry and video platform. The nose cone has a large compartment for telemetry/GPS and I added a Mobius camera shroud for video.

Obviously, I knew nothing about making fin fillets and had never worked with epoxy before.

While it flew straight and true, it looks awful. I've improved since then, but I would like to save this rocket for sentimental reasons. I tried sanding the fillets to remove them, but no joy. The epoxy is hard as cement. Even the Dremel tool couldn't make a dent. I have considered making larger fillets over top of them. But not sure if that will work.

If you can stop laughing and pointing long enough, I'd love some suggestions. Grateful for the wisdom of more experienced rocketeers.

I ain't nobody and I don't know nuthin', but I would'nt have touched it again. I'd have kept it hung up right next to my newest project always as perspective. And then I'd always remember from the abortive sanding, et al. scars of the time when I thought I needed to "fix" it. :)

Kinda hope that is what you chose.

Be well!
 

BSNW

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Purchase some Bondo spot putty. It comes in a big tube and is red. Using a large popcycle stick, cover your "bad" fillets. Then as described above, with a dowel or your hand, sand smooth. Do this outside as it is very dusty. It will be glass smooth. When done, tack off dust, saturat with thin/watery CA. Sand again with 400 grit. It will be glass smooth.

Andrew
 
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