Nice Even Fillets

What is the secret to making nice even fillets? My best results came when I have added wood filler and sanded. Now it is a matter of getting each fillet the same. I am working on finishing my ISP Caliber, but this question is for all rockets in general.



Randy
NAR #80885, L1

I put a strip of tape right where I want the edge of the fillet to be. Then, depending on the type of rocket, I use gel or 5, 15 or 30 minute epoxy. With a small model rocket, I attach the fin with CYA and put on a small fillet of 5 minute epoxy. The epoxy seeks its own level and dries real sooth. You do have to make a tape "dam" at the ends of the fillet. If you use epoxy gel you don't need a dam. Apply it with a finger, wait until it is partially set in three or so minutes, and smooth with a finger dipped in alcohol. Then peel the tape off and the fillets will be smooth and perfectly defined.
I use CYA/epoxy for all fins. The carpenters glue doesn't seem worthwhile to me. Takes too long to dry, and since it shrinks, fillets can be uneven. CYA/epoxy is just as strong or stronger. I sometimes use polyurethane glue for internal assemlbies, but it expands while drying, so make sure that it won't be visible.

Originally posted by rbeckey
I put a strip of tape right where I want the edge of the fillet to be.

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So you use tape on both sides of the fillet, body tube side and fin side? You are just measuring a given distance from the actual point where they meet? Like 1/4" away, to give youself a 1/2" fillet?



Randy
NAR #80885, L1

Yes, I put the tape on the fin and BT. I usually eyeball it on most models, but there is no reason that you can't measure it. For the most repeatable results, I'd use a scrap of balsa or something as a gauge to make the marks. It is really pretty easy to lay the tape parallel to the fin/BT joint even without guide marks. I use blue painter's masking tape. It seems easiest to work with. Remember to leave one end of the tape pulled up for easy removal.

I am building (and adding fillets) with white or yellow glue. One characteristic I have observed is that after pouring fillets, the glue dries, in some spots, more quickly and creates pits or dips in the fillet. I now thin my glue a bit with water and don't try to get the whole fillet added in one pour. Works better for me.

When all else fails and I get a bad fillet, I thin some fill n finish and paint it on with a small brush. After it dries I sand it and everything looks perfect. After its painted, its all the same.

about the smothing with alchol on your finger, (sorry don't know how to quote). I don't think that would be a good idea if you are using a Quantum tubing airframe it could distort the body tube

Originally posted by rbeckey
For the most repeatable results, I'd use a scrap of balsa or something as a gauge to make the marks.

Remember to leave one end of the tape pulled up for easy removal.

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Ok, I will try this on my next rocket. I have already started the fillets on my Caliper. I was talking with a guy at work and he suggested a way to improve the wood filler method. Apply the wood filler, more than you will need. Then take something like a quarter and drag it along the joint between the body tube and fin. The rounded edge should leave an even amount of filler. Maybe???


Randy
NAR #80885, L1

Anything with a curve. Smoother is better. Quarters have ridges that will leave grooves. Popsicle sticks work great, as do fingertips, plastic utensils, etc. Wet the object first. Rewet often.

use a spoon. You get the same fillet every time and the spoon picks up all the excess.

I've tried all these methods and they all work great and they require little if any sanding. Tongue depressors and popsicle sticks make great fillets. The one I like best is the spoon technique. The epoxy rolls to the inside of the spoon and deposits less on the bodytube. I usually lay tape along the joint to keep the excess off the parts. After removing all epoxy possible with the spoon and when the epoxy gels I generously work the entire length of the fillet with my finger wet with alcohol, and I don't spare the alcohol. The fillets on my mini-Armageddon are the best I've done. They came out uniform and very smooth. Rocketmaniac, try a lot of different techniques to find the one that works best for you.

Oh yeah, any pics?????

Swimmer

On small and medium size rockets I use bondo spot putty ..applied with a finger to finish the fillet...the stuff usually dries too fast to use a spoon or shaped stick...I use it mainly to fill the uneveness in yellow glue fillets...sands very nicely

with epoxy, on larger stuff, I use the masking tape and plastic spoon method.it really helps keep the excess from spreading to the edges..than sometimes just a bit of spot putty if needed

I've noticed that fill n finish works almost as well as spot putty on really small fillets

I've also learned not to put the yellow glue on too thick, it will definately leave those dimples

Does anyone else use the following technique?
on most model rockets I use cya to attach the fin ..it makes the yellow glue fin fillet process go so MUCH quicker.

Has anyone tried JB weld besides me? I have used it on just about every rocket I've built since I got back into rocketry. It pretty well stays put and surprisingly sands easy once good and dry.........Larry

Originally posted by Swimmer
Oh yeah, any pics?????

Swimmer

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I am working on get understanding my digital camera, so new pictures? No, but I do have the photos of my Level 1 flight taken at our clubs Jan 2003 launch. My website is: https://rocketmanic66.tripod.com/

Randy

Originally posted by Larry
Has anyone tried JB weld besides me? I have used it on just about every rocket I've built since I got back into rocketry. It pretty well stays put and surprisingly sands easy once good and dry.........Larry

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I use JB Weld anytime I need to attach a metal part like a motor retainer. Its too expensive to use for all applications. I normally use CA to tack a piece down and then Bob Smith epoxy to finish up on small applications. For large applications like fiberglassing, I use West Systems epoxy.

Tacking the fin with CA is soooo helpful. I remember when I didnt have any and needed to just use white glue...what a mess!! I have used JB weld and regular epoxies but the one that I have found works best is PC-11. It is an epoxy paste and works perfectly for the fillets and any other place.

The stuff is so strong I tried to break two peices of plywood that it had bonded and couldnt. Even when I put it in a vise and hit it with a hammer it didnt come apart, however, the wood did eventually break.

It is super strong and I find the best part about is how thick it is and how long it takes to dry. It has a thickness equal to bondo and, therefore, it won't run so you can fillet all your fins in one sitting. It takes around 24 hours to dry completly, about 2 to start to harden, so you have plenty of time to play with it

Is PC-11 sandable? Where do you get it?
Thanks