Help with filets please!!

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Vance in AK

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I'm in the process of putting the filets on the fins on my Super Big Bertha.
I was going to use epoxy clay, but wasn't sure I had enough so I went with good old yellow Elmers wood glue. My standard.
Here's the problem.
I'm ending up with large voids (air pockets) in the filet when it dries. I guess some of this is probably from shrinkage.
I dig out the voids as best I can, & then go back & fill them, but then I end up with voids & large "pin holes" in the glue I just put in to fill the void.
What am I doing wrong?????
Is this why some of you use 15 min epoxy?
Thanks.
Perplexed(Vance) in AK.
 

Stymye

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sounds like the application is too thick
 

Vance in AK

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You could be right stymye.
It makes sense. The fins and BT are larger than I norally work with, so the area the filet ended up covering was wider which also means it was probably deeper.
Hmmmm.... could be it.
That brings up another question. How big do your filets end up on this size rocket?
Would they be the same size as on say a standard Big Bertha? Does you filet stat the same size regardless of Rocket size or does it maintain some type of ratio dependent on BT size?
Thanks.
 

Stymye

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correct fillet size is basically what ever you like

aerodynamically speaking, the fillet should be 4-8% of the fin root chord for best performance( friction,drag, ect...)

to use the yellow glue on larger fillets you will have to build up the fillets to the size you want rather than try to make bigger fillets in one pass , no question the dimples are from too much at once...I have my share of dimple filled rockets,it's not hard to put too much

hope this helped
 

Steward

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One tip I can offer...keep the white glue warm...not hot..., but warm...try refraining from shaking or anything else that might cause bubbles in the glue...work slowly!!! Also my fillets tend to be uniform simply because I always use the same side of the same finger when smoothing the fillet out...
 

vjp

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I think normal, wood-glue fillets are fine on anything up to BT-80 sized projects, but I wouldn't attempt to 'scale up' the size of the fillets. 3/16" is about the max width for a wood glue fillet, no matter the size of the tube/fins.

The way I avoid getting air pockets under the glue (which is what causes the 'holes' in the fillets when they dry) is to use the tip of the bottle to inject the glue tightly into the fin-BT joint, moving the tip SLOWLY along the joint so that capillary action draws the glue right into the joint. By slowly I mean about 1/8" per second, this gives the glue time to get down into the joint. Then after all fins are glued, I smooth out the fillets with a fingertip. I rarely ever get an air pocket or void this way.

I think brushing the fin-BT joint with a watered down glue solution before applying the glue would help to 'wet out' the joint and prevent air bubbles too. It's an idea I've been meaning to try out, if anyone else tries it first I'd be interested in hearing your results.
 

Vance in AK

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Thanks for the help guys. I love this place. Less than an hour & 4 helpful answers.
I think you guys are right. Too thick.
Also Steward may have a point on temp. The temps outdoors have been around 0 so my garage only gets up into the 50s.
I'm just kind of disapointed. I wanted this to be my best attempt so far & it hasn't turned out that way. Let's hope it flys better than it looks!
Vance in AK.
 

sandman

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Vance,

Don't give up so easily.

The fillets are probably more than strong enough as they are even with the pinholes and dimple. That probably won't hurt the final strength.

Try filling the dimples and pin holes with Elmers's Fill 'n Finish.

Do several applications sanding in between and you should wind up with fillets you will be proud of.

sandman
 

Vance in AK

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Thanks for the encouragement Sandman.
I hadn't thought about that. Will the Fill 'n finish adhere to the dried glue well?
Vance in Ak.
 

sandman

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Gee,

Will Elmer's stick to Elmer's?

It sure will!

If you have doubts just kinda wipe it with a little water...not much.
Like just with a wet finger.

sandman
 

Vance in AK

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Thanks for the help guys. I'll give the Fill ', Finish a try sandman.
Vance in Ak.
 

cydermaster

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Originally posted by Vance in AK
Let's hope it flys better than it looks!
I'm sure she will - I've made many a cock-up on my birds, and they've ended up flying just great.
 

Ryan S.

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I have used bondo to fill the holes and another thing that works great is Phenoseal. It comes ina caulking container. It is actualy a very strong glue and is perfect for making fillets because it is thick.
 

Vance in AK

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Thanks guys.
I'm using Sandman's idea of the Fill'n Finish 7 it seems to be working great.
Thanks for all the great advice.
Vance in Ak.
 

seo

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Vance-

I too have had trouble with yellow glue in low temps. I have found it best to keep the area where youare working at 60 degrees or better. Also need to maintain the temp during the drying phase.

Scott
 

bsexton

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If I want bigger fillets I use epoxy or epoxy clay. I used epoxy clay on my Super Big Bertha and she has flown on E, F and J composite motors with no problems.
 

Vance in AK

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Thanks again for trhe help guys. I think I'll do my yellow gluing in the house on those really cold days.
Bruce, I was going to use Apogee's epoxy clay, but wasn't sure I had enough. My mistake, as afterwords I decided I probably did.
Next time.
Vance in AK.
 

Vance in AK

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Scott, I meant to ask you if know a cousin of my wife's that lives in Snohomish. His name is Grady Kringen, & He's a pastor there.
Yes I realize that Snohomish isn't small enough that you know everyone, but I figured it was worth a shot.
Vance in AK.
 

seo

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Originally posted by Vance in AK
Scott, I meant to ask you if know a cousin of my wife's that lives in Snohomish. His name is Grady Kringen, & He's a pastor there.
Yes I realize that Snohomish isn't small enough that you know everyone, but I figured it was worth a shot.
Vance in AK.
Sorry don't know him. What church is he at?

My address is Snohomish but I don't live within the city limits. I am about 7 miles south of Snohomish, Maltby/Cathcart area.
 

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