Fin filleting technique needs help...

[bigone5500]

I think I need to revamp my filleting technique as it seems I'm using too many steps to get it done...but I do get it done. Here is a list of steps I use in filleting a 4 fin rocket:

1. make tick marks to get tape at equal distances from fin root on both BT and fins.
2. apply masking tape to fins and BT
3. mix enough epoxy to do one fin in a medicine cup
4. apply epoxy with a popsicle stick and spread with rounded end to obtain rough fillet
5. remove tape from fin sides and at BT. also at rear of fin (epoxy dam)
6. dip gloved fingertip in alcohol and smooth out fillet on both sides.
7. build up leading edge of fillet by adding epoxy where needed and smoothing with finger.
8. wait for epoxy to set up so rocket can be rotated without the it running down
9. repeat step 1 for rest of fillets

I really hope there is a better way...

*edit*: I forgot to mention that I am using US Composites 150 thick resin and 4:1 fast hardener

 

[Stymye]

you can use a filler to do them all at once

 

[bigone5500]

Dang it!!! I knew I'd forget something...I also use microballoons. I use a little more than the instructions say. It calls for a 3:1 ratio of epoxy to balloons but I use a touch more...I wouldn't say 2:1 though. I have to let the epoxy set up a little before I apply it too. Otherwise it wants to run like syrup.

Should I use more balloons with the epoxy? If so, what ratio?

 

[Stymye]

I use Prather brand, it calls for 3 parts microballons to 1 part mixed epoxy.otherwise it's way to hard to sand.
but I only use microballons for filling ,not the actual structure fillet.

For the structural fillit I like the microfibers.and mix it like peanut butter.

basically start with a strengthener and finish with a filler if necessary

 

[bigone5500]

So does the brand of balloons make a difference? I am using Top Flite brand. They should be the same as others right?

 

[powderburner]

Using microballoons mixed in with epoxy is definitely the right thing to do; the fillets are easier to sand, they are lighter, and the rocket is slightly more stable (c.g. moves forward, however so slightly).

Here is one other idea that improves one more level on all these points---use lightweight spackle. It is ridiculously easy to apply and shape (just add a couple drops of water to extend working life); you can use the exact same tools to drag across the surface and create that 'special' radius. Spackle is even easier to sand. It is much less dense, and therefore much lighter. If you don't like what you create, in many cases you can scrape almost all of it right off (try THAT with epoxy!). And when you get the shape that you want, you can toughen it and put on a shiny cover coat with a thin layer of CA or thin epoxy. Extend that cover coat and feather it onto the surrounding airframe tube and this stuff will stay put pretty well.

The lightweight spackle I am talking about is the stuff sold in your local hardware store for wall and sheetrock repairs. It usually comes in a plastic tub that looks just about the same as regular spackle but when you pick it up it feels like the plastic tub is empty. It has a latex base and can be worked with water, and has the same microballoons mixed in to reduce the density. Once it dries it will readily absorb CA or thin epoxy. If you haven't tried it, you really should.

And it works great on walls, too.

 

[Stymye]

So does the brand of balloons make a difference? I am using Top Flite brand. They should be the same as others right?

the prather brand I use are phenolic beads ( dark purple) I believe the top flite are glass beads because of the white color. but they work the same way.
they are both ideal for mixing with epoxy to create a sandable filler

 

[bigone5500]

is phenolic easier to sand? I haven't tried to sand these glass ones yet.

 

[zog43editor]

I usually don't do 1 fin at a time when making epoxy fillets, but work on the the opposing faces of two fins. What's the working time on the epoxy you are using? I also tend to use 5 minute stuff for fillets since they aren't typically structural and so the wait time for when I can rotate the tube is less.

kj

 

[JRThro]

So does the brand of balloons make a difference? I am using Top Flite brand. They should be the same as others right?

I read the warning on the label, and it says, "CAUTION: EYE MAY CAUSE SKIN AND EYE IRRITATION". I wonder how long it's been like that, and what other errors are on the label.

:surprised:

 

[bigone5500]

I usually don't do 1 fin at a time when making epoxy fillets, but work on the the opposing faces of two fins. What's the working time on the epoxy you are using? I also tend to use 5 minute stuff for fillets since they aren't typically structural and so the wait time for when I can rotate the tube is less.

kj

I think it's 15 mins working time. But I have found that time to be less when adding more balloons. I have been able to do 2 fins at a time by adding a 50/50 ratio of balloons to epoxy. This seems to make the mixture thicker and causes it to set up faster therefore making it less runny and therefore making me have to hurry up that much more... With that mixture I get about 10 mins working time before it gets too thick to work with.

JRThro: If you take your eye out, then dip it in the balloons and then rub it on your skin, you will get eye causing skin irritation...