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  #51  
Old 07-02-2010, 03:51 PM
stefanj stefanj is offline
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Before applying epoxy fillets, make little "dams" of masking tape fore and aft end of the joint.

Set up a place where you can keep the body tube horizontal, somewhere where it won't be disturbed for the cure time plus a couple of hours.

I apply epoxy fillets using a BBQ skewer. Dip the tip in and run it along the body tube / fin joint. Repeat until you have a bead of constant thickness along the joint. Poke out any bubbles.

Use your finger, inside plastic gloves (or even a layer of plastic wrap) if you want to be careful, to smooth out the fillet.

Use a shop tissue or rag dipped in alcohol to clean up messes.

You can apply two fillets at once, on "facing" fins. The body tube segment between the two fins is placed facing straight up. Once you have the fillets smoothed, gravity will do the rest once you mount the tube horizontally.

After the epoxy is well set, but before it is hard, you might want to remove the tape "dams" use a blade to scrape away any drips.

Repeat the process for the other pairs of fillets.

After the epoxy is well and truely set, sand the edges smooth. If necessary, use putty (or epoxy with microballoons) to fill in gaps and any irregularities where the leading edge and trailing edge meet the body tube.
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  #52  
Old 07-05-2010, 02:44 AM
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Mark II Mark II is offline
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I probably have a very different take on environmental issues than does GH, but even I am a very big fan of using butyrate dope on balsa fins. In fact, his many posts on the subject prompted me to try it out again after all these years, and now I won't go back to using anything else. The results are that good. I was never very enamored of using FnF on either fins or nose cones; to me, the product is meant for one thing - filling tube spirals. On nose cones, I use laminating epoxy as a grain filler and surface hardener. But dope absolutely rocks for balsa fins. Maybe I've killed a few too many brain cells, but to me it only has a moderate odor, not terribly overpowering or even unpleasant.

I use Dap Plastic Wood to repair damaged fin edges. It is by far the best repair putty that I have ever found for that purpose. Recently I repaired a small split on the edge of a glider wing with thin CA. After that had cured, there were still some small gaps in the surface on both sides. I filled them with Plastic Wood and sanded the area smooth. A couple of days later I took the glider out to inspect it and I had a very difficult time locating the site of the repair. It was indistinguishable from the natural wood in the wing.

I am a bit concerned about using plastic wood as a grain filler for balsa nose cones. The reason is that after it cures, it is much harder than the balsa. If any balsa is still exposed, it will sand away readily while leaving the plastic wood behind, which is exactly the opposite of what I want to happen. I have used it on occasion to fill deep gouges or dings in nose cones, and it does a very good job. In my book, though, far and away the best filler for surface repairs in balsa (especially nose cones) is Aeropoxy Light Filler. For nicks and chips in fin edges, though, plastic wood is the one to use.

I don't encounter bubbling through in my fin fillets because I do all of the filling and sealing of the fins before I bond them to the rocket. So the fillets always go over the dope, and not vice versa. I use an oral syringe to lay down the fillets, and then smooth them with a gloved finger. I do like to use Titebond Molding and Trim Glue for fillets on occasion, but I always get the best results with 30 minute epoxy.
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  #53  
Old 07-05-2010, 06:41 AM
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jeffyjeep jeffyjeep is offline
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Quote:
Originally Posted by stefanj
Before applying epoxy fillets, make little "dams" of masking tape fore and aft end of the joint.

Set up a place where you can keep the body tube horizontal, somewhere where it won't be disturbed for the cure time plus a couple of hours.

I apply epoxy fillets using a BBQ skewer. Dip the tip in and run it along the body tube / fin joint. Repeat until you have a bead of constant thickness along the joint. Poke out any bubbles.

Use your finger, inside plastic gloves (or even a layer of plastic wrap) if you want to be careful, to smooth out the fillet.

Use a shop tissue or rag dipped in alcohol to clean up messes.

You can apply two fillets at once, on "facing" fins. The body tube segment between the two fins is placed facing straight up. Once you have the fillets smoothed, gravity will do the rest once you mount the tube horizontally.

After the epoxy is well set, but before it is hard, you might want to remove the tape "dams" use a blade to scrape away any drips.

Repeat the process for the other pairs of fillets.

After the epoxy is well and truely set, sand the edges smooth. If necessary, use putty (or epoxy with microballoons) to fill in gaps and any irregularities where the leading edge and trailing edge meet the body tube.

That's a VERY thorough procedural description. I especially like the BBQ skewer. One thing I'd like to add: on some scale builds--where there shouldn't be any fillets apparent, I use a long cure time epoxy and a toothpick or sometimes a finishing nail to apply very subtle--almost invisible fillets using just one drop of resin at a time, and then use my pinkie to smooth it.
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  #54  
Old 07-05-2010, 11:23 AM
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LeeR LeeR is offline
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Quote:
Originally Posted by jeffyjeep
That's a VERY thorough procedural description. I especially like the BBQ skewer. One thing I'd like to add: on some scale builds--where there shouldn't be any fillets apparent, I use a long cure time epoxy and a toothpick or sometimes a finishing nail to apply very subtle--almost invisible fillets using just one drop of resin at a time, and then use my pinkie to smooth it.


When I was into HPR, big fillets were fine, since one would typically go for strength, and a nice smooth, rounded look. Like jeffyjeep, I go the minimalist route now (but for all builds, scale or not), whether using Titebond Trim and Molding glue, or epoxy. On epoxy, I found that a simple, effective procedure is to run the fillet normally along the fin-tube joint, but remove it with a gloved finger dipped in rubbing alcohol, or lacquer thinner, then running my finger along the joint to remove most of the epoxy, leaving a nice clean, almost invisible fillet.. I buy the blue nitrile gloves by the box of 100 at Harbor Freight, perfect for keeping hands clean, yet allowing good tactile feel. (For wood glue fillets, I still use the same method, I just don't bother with a glove.)
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  #55  
Old 07-05-2010, 11:31 AM
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jeffyjeep jeffyjeep is offline
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Hmmmmm. I've NEVER used a glove. Am I going to die (from this--I mean?)
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  #56  
Old 07-05-2010, 12:10 PM
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GregGleason GregGleason is offline
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You are not going to die, but life could be not as much fun if you develop an epoxy allergy.

http://dermnetnz.org/dermatitis/epoxy-allergy.html

I have used nitrile gloves, but it was more of a personal preference. But according to the data, vinyl (and especially rubber) gloves do not perform as well as nitrile.

Greg
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  #57  
Old 07-05-2010, 12:39 PM
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LeeR LeeR is offline
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Greg is right, and I'm living proof. I have to be careful to exposure from a number of chemicals on my hands. I also tend to be much more sensitive to the sun. Maybe just all those years as a kid getting roasted during the summer.

Once you get used to working with gloved fingers, it is not too bad. Fortunately, most of the nitrile gloves I've tried are pretty thin, and so you can get pretty decent results with a little practice.
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