Quantcast

Fin leading edge joint fillet?

The Rocketry Forum

Help Support The Rocketry Forum:

Bravo52

Well-Known Member
Joined
Jan 18, 2009
Messages
681
Reaction score
2
So, how does everyone treat the leading edge of their fins where they join the body-tube. Even on the small rockets, it's hard to create a smooth fillet around the joint. How do you do it?

finroot.jpg


finroot2.jpg
 

rokitflite

Well-Known Member
Joined
Jan 18, 2009
Messages
5,155
Reaction score
2
So, how does everyone treat the leading edge of their fins where they join the body-tube. Even on the small rockets, it's hard to create a smooth fillet around the joint. How do you do it?

I use epoxy and smooth it aroung the leading edge with my finger... Jeeeze are you on vacation again Jerry? You seem to be posting an awful lot recently...:p
 

foose4string

Well-Known Member
Joined
Jan 18, 2009
Messages
2,853
Reaction score
7
Sometimes, I'll use a toothpick to apply a little dab of glue to that area. Then, smooth and take off excess with finger. Other times, I've left left that edge "clean", only filleting the sides of the fin and using a paper towel to wipe away the extra bit of glue that gets dragged to the front(or rear). Depends on how ambitious I feel.
 

powderburner

Well-Known Member
Joined
Jan 18, 2009
Messages
7,401
Reaction score
4
First, I don't like to leave my fin edges square. Even if I don't sand in some fancy airfoil shape, at least I round the leading and trailing edges.

Which may or may not make any difference in the following.

If I want to make a fancy fillet, I don't use glue or epoxy. Glue is too erratic in its behavior when drying, as in, it usually dries/shrinks into some goofy shape that I didn't want. And it is too tough to sand easily without damaging the surrounding cardboard or balsa. Epoxy is too heavy, too brittle, and too incompatible with too many primers and paints.

If I want a fancy, nice-looking fin root fillet, I break out the light-weight wall spackle, the kind that has the glass micro-balloons mixed in, where the full tub on the store shelf feels empty when you pick it up. This stuff mixes and thins with water, so you can flick a few drops onto the top of the tub and stir to re-activate a dried-out tub, or wipe with a wet finger to reshape a fillet. It sands very easily, and when you get the shape you are happy with, it absorbs CA quite well, and primer sticks on top very well also.

I just shape it around the front of the fin root....but mine are usually more round.
 

jef955

Well-Known Member
Joined
Apr 16, 2009
Messages
255
Reaction score
0
Never bothered with mine. And I have never felt that I lost any strength. My lawn darts usually work just fine :eyepop:
 

JOAT

Member
Joined
Jul 26, 2009
Messages
6
Reaction score
0
So, how does everyone treat the leading edge of their fins where they join the body-tube. Even on the small rockets, it's hard to create a smooth fillet around the joint. How do you do it?
Never had a problem making the glue fillet continuous from the sides wrapping around the front. Just fill the corners with glue all around and wipe with the pad of your finger. Continue the motion around the front and you get a wrap around fillet.
 

JRThro

Well-Known Member
TRF Lifetime Supporter
TRF Supporter
Joined
Jan 18, 2009
Messages
4,056
Reaction score
0
Location
Houston, TX
I usually let the fillets along the side of the fins dry first (which most often takes 3 rounds of filleting with white or yellow glue, whichever one I happen to be using on the rocket). Then I apply a drop of glue to the leading edge joint and smooth it with my finger. This might take 2 or 3 rounds as well, before I get it looking halfway decent.

Also, when I'm sanding the root edges of a set of fins to even them up, I seem to be incapable of sanding them without developing a slight curve from the leading edge of the root to the trailing edge. So there's almost always a bit of a gap between the leading edge of the fins and the body tube, and between the trailing edge of the fins and the body tube, so I need to fill that in with glue anyway.
 

FatBoy

Random Part-time Hobbyist
Joined
Jan 18, 2009
Messages
897
Reaction score
18
I do the same thing JOAT mentioned. Then after the glue has dried, I use some watered down wood filler to help smooth it all out.
 

Attachments

FatBoy

Random Part-time Hobbyist
Joined
Jan 18, 2009
Messages
897
Reaction score
18
Thanks, Kit. But it really isn't hard to get smooth fillets - just a little work... filler, sand, prime, sand.....

I use a dowel or chopstick or round pencil (depending on the fillet size you want) as a sanding block with a piece of sandpaper rolled around it with the rough side out.
 
Top