Fin Fillets - Alternate Material

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Hospital_Rocket

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I have been using the milled glass, epoxy, plastic spoon approach I read about here with mixed success. For the most part the fillets are ok, just not consistent in geometry from joint to joint.

I have modified the process slightly to use a spray bottle of alcohol to wet down the tacky surface allowing it to self level.

All that aside, has anybody experimented with the 2 part light weight body filler from Bondo to build fillets? It sands real easy, has a lightnig quick set time, and takes a finish like all get out. I've heard people complain that it sets too fast however I would just mix very small batches, overapply and sand to taste.

Any body want to discuss it?

A
 

DynaSoar

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Originally posted by Hospital_Rocket
I have been using the milled glass, epoxy, plastic spoon approach I read about here with mixed success. For the most part the fillets are ok, just not consistent in geometry from joint to joint.

I have modified the process slightly to use a spray bottle of alcohol to wet down the tacky surface allowing it to self level.

All that aside, has anybody experimented with the 2 part light weight body filler from Bondo to build fillets? It sands real easy, has a lightnig quick set time, and takes a finish like all get out. I've heard people complain that it sets too fast however I would just mix very small batches, overapply and sand to taste.

Any body want to discuss it?

A
I read of Bondo being used in a best-of tips & tricks book I got from NAR as well as on EMRR. Haven't tried it. I'm having plenty of luck with the JB Weld putty from Apogee. Very long work time and water solubility gives me plenty of time to get it into the shape and surface I want so I don't need to worry about sanding.
 

KarlD

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So far, my experiments with finishing epoxy with micro-balloons as filler have been going well. Sandable mix, plus it is thick enough to be easily shapeable with the old latex covered little finger.
 

RocketboyG80

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I think you mean Fix-It epoxy clay DynaSoar, I don' think Apogee sells JB weld. I too have has much success with Fix-It. On medium to large size rockets I use it to make permanent aerodynamic epoxy dams at either end of the fin. I then pour West System into this canal until it it is level with the dams. I then sand the the slight edge where the epoxy meets the Fix-It clay. The result is one uniform fillet. Note- I make all the epoxy clay dams at once so that they are all the same size and shape.
 

midpwrguy

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With all that you have asked over the last few months (HR)
This is one I think I've got somthing to add to.
I've done like the other guys here building dams to do the fin filets in epoxy. But I think I've found the best way to do fin filets.
( for Me) What I get for this is call fiberglassing jelly. Made by
Bondo. This stuff has fiberglass in it already.You can get it at wall mart. Then I always get the extra tube of hardner.
they never give you enough hardner for the size of can you get.
When I mix it up. I just do enough to do one or two fins. I found that if you mix it up to where it has a brown color to it.
It will give you enough time to spread it out. Green not enough
hardner. Red to much. Sets real fast. I use a small pice of floor tile
to mix it on. That way if I dont get the extra off it in time before it sets. I just take the belt sander to it and take it off. Then you can get some spreaders they use for this stuff. A pack is only a few dollars. This is what I use to get the shape I'm looking for. Just cut them to the size of fin filets you want. spread one or two fins
let it set and cut the extrs off with a knife. You wait to long. You'll have to do some extra sanding. With the cold weather it takes longer for it to set. So I'll just take the hair dryer and help it along.
After having done all the fins. I take drill bit the size I want them to be and sand them down.Just rape a small pice of 60 or 80 grit sand paper around the drill bit. You have to be careful at this point. Not to sand into the fins or the body tube. After having done the fin filets. If I'm going to fiber glass a rocket this is when I do it. I'll post a few pictures of some of the fin filets.
 

midpwrguy

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When I start I'll do fin filets out of epoxy. Small ones (sand)
Then afterhaving done that. I shape them with the bondo.
Here's a hawk mountain Raptor. that I did like that after having
done the fin filets out of epoxy.need the pic!
 

midpwrguy

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This is a picture of a 3" rocket. Where you can see how It looks.
After the fiber glass has been done.
 

midpwrguy

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This is just to show. The diffrent size of spreaders. Works predy good just to cut them out with some sissors.
 

Stymye

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thats interesting ...bondo is a polyester based product that is not at all compatable with epoxy,,, 2 very different things

also a pure bondo fillet would dry and crack over time ..it would needs a layer over it...plus it's very heavy stuff , designed to be used in a thin layer

If you were glassing a bondo fillet you would normally want to use use a polyester resin.... right..?

otherwise why not use a epoxy and filler/microballoon fillet that would be compatable with epoxy/glass
putting epoxy over bondo or vice versa doesn't make sense

it might work, mabey it does, but it's not designed to.
 

midpwrguy

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It's not a pure bondo filet. The bondo is just to give it the shape
I want. I've already done the filets in a epoxy. And yes it does work with Fiber glassing . It's used on repairing boats. says it
works with metal,wood, plastic and fiberglass surfaces. Never had a problem with it cracking or the glass pulling away from it.
these pictures are of two rockets that have been out in the shed
for two years. From tempertures of 20below to 120. So you'd think if it was going to do it. you'd see it by now.
 

Stymye

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I guess the proof is in the fillets, for some reason I always thought they were incompatable. mabey I'm thinking of a different type of bondo product. you know me ,If have a question I ain't afraid to ask
 

Hospital_Rocket

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MPG:

The stuff I got my hands on was a light green body filler, It's not that red goo that weghs a ton. The process I waanted to follow was to:

Mechanically mount the fins. I was going to lay up 3oz glass in a strip along the edge.

After that cures use the epoxy/glass slurry to get as close as I can to a good fillet

then it's Bondo time! I mean If I going to go thru the trouble to build and lose a rocket, I want the person who finds it to say, "wow dunno who built this but they take pride in their work"

I think am considering using a technique you are using.

Amazing, great minds think alike!

Wow, I was able to stump you for this long? :p
 
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