Careful Fin Removal

OK, I searched for "fin removal" and nothing came up (got a few hits for adhesive removal, glassine removal, paint removal, and even retainer removal...).

So what is your technique for delicately removing a fin without destroying the tube?

In my case, I have a scratch built BT-55 cardboard tube with balsa fins glued with Elmer's wood glue onto the tube exterior, and Elmer's wood glue fillets. I want to remove all of my old fins and replace them with new fins, but I don't want to mess up the tube and I want to be able to place the new fins in the exact same old locations.

I am thinking of cutting the balsa at the fillet, then using a dremel with a sanding drum and just working on the remaining fillet, root edge balsa, and root edge glue, without getting into the tube (too far at least). I know I don't have a lot of tube wall thickness to play with, so that's why I wanted to ask if there was a better way before I dive in and regret it.

Thanks in advance for sharing your ingenuity.

Why put new fins on an old body tube?

You can get 34 inches of brand new BT-55 for a couple of bucks at www.balsamachining.com

Cut the motor mount out of the old tube and put it in the new tube along with the new fins.

I'm curious, what makes this rocket so awesome that you wouldn't just build a new one?

Theoretically (if properly done) the glue joints should be stronger than the fins or body tubes themselves, so removal of the glue would almost have to potentially cause some structural damage to the body tube no matter what method you use.

Why not just salvage the nose cone and rebuild from scratch, or cut the body tube and swap in a new fin can?

That said, I'd try what you said -- trim the fillet and try to sand down the residue.

I usually remove my fins quickly and abruptly. Hard landings. I don't know of a delicate way either.

A dremel can get away from you quickly and damage the tube. I wouldn't trust myself not to mess up.

You may have to get creative. Like cutting the fins back to look like ribs/conduits and then just shift the placement of the new fins in between your new ribs/conduits.

The only other thing I can think of is to cut off the bottom of the rocket, fins and all and using a coupler you can attach a new short piece of body tube to attach your new fins to.

Short of that IDK.

Hopefully someone else will come along with a better idea.

I'll be watching this thread. If there's a better way, I would like to know too.

David

Thanks for the quick replies. I love this place.

Why, why, why, LOL. I figured you guys would rib me. I have a flame paint job on this puppy, with a gradient from black, to red, to orange, then yellow, and white. I wanted the least amount of hassle on a repair. It's not even a year old and I've broken the fins 3 times. Once I was able to find the broken part and glued it back on, the next time I broke a fin I was able to cut the fin into a different shape and just cut the other two to match (still stable, but kinda ugly...to me). This time it's beyond saving and I am switching to basswood and a design that keeps the fins above the motor.

I'm sure another why is coming: The answer is because the rocket is heavy, the chute is small, and the fins were long, light balsa that just had not fared well. (The question was gonna be: why do you think the fins keep breaking?)

I guess short of an elegant technique, if I muck it up, I could always salvage parts and build new (or shorten).

I like the ribs idea and was going to do that, but I have a launch lug in the way between the fins...but, that could be more easily removed than 3 fins!

455 Buick said:

Thanks for the quick replies. I love this place.

Why, why, why, LOL. I figured you guys would rib me. I have a flame paint job on this puppy, with a gradient from black, to red, to orange, then yellow, and white. I wanted the least amount of hassle on a repair. It's not even a year old and I've broken the fins 3 times. Once I was able to find the broken part and glued it back on, the next time I broke a fin I was able to cut the fin into a different shape and just cut the other two to match (still stable, but kinda ugly...to me). This time it's beyond saving and I am switching to basswood and a design that keeps the fins above the motor.

I'm sure another why is coming: The answer is because the rocket is heavy, the chute is small, and the fins were long, light balsa that just had not fared well. (The question was gonna be: why do you think the fins keep breaking?)

I guess short of an elegant technique, if I muck it up, I could always salvage parts and build new (or shorten).

I like the ribs idea and was going to do that, but I have a launch lug in the way between the fins...but, that could be more easily removed than 3 fins!

Click to expand...

You pretty much nailed the procedure in your first post. I'd use at least two layers of blue Painter tape or Frog Tape as a barrier on all areas around the fins to protect the finish while cutting off the old and sanding down the fillets. Don't worry about taking the fillets down to absolute zero as you can add the new fins with or without tabs by adding "epoxy rivets" to the body tube and root edge (even if only the diameter of a straight pin). Remove the tape as soon as practical to prevent any further damage to the body paint.

John - what do you mean about epoxy rivets? Meaning I should drill some holes in the body tube and the root edge so there are some "teeth" in the shear plane when I re-glue?

Also, a thought would be to not try to completely remove the glue, but rather that new glue on dried glue might be stronger? As you guys said, it would just weaken the body tube if I tried to get down to it (i.e., zero old glue left and zero entry into the cardboard).

Will post some pics of my butcher job soon...

So this is the only pic I have of the rocket showing the fins intact before paint after the initial build (I took it for a different post last year).


Like I mentioned before, I repaired the fins once, when I found the piece next to the rocket in the field (probably broke on landing). I broke a fin a second time and ended up cutting the broken part of the fin into a straight line, and did the same with the other 2 fins (I hated the look, but it kept the rocket flyable. This is a pic of the 3rd fin breakage, but shows the UGLY 2nd generation fin.


Here I used a cut-off disc on my dremel, just to get close to the root/fillet. Glad to lose those ugly fins.


I used a drum sanding attachment on my dremel to get it to this point. I still have quite a bit of glue and fillet left, as I did not want to get into the cardboard. Also, I was thinking I would block sand the rest of it so I would get a nice flat surface. Thought about my belt sander, but that's too fast and one slip is all it would take to mess up the tube or the paint (paint is my weak point, and that's why I'll do anything to not have to go through another whole-rocket paint scheme).


I keep this in my Dremel tool kit so I can slow the speed; Without it, I would have gone too far too fast.

little surprised that no one mentioned that a few drops of vinegar will soften white/yellow glue fairly rapidly.
Rex

Rex R said:

little surprised that no one mentioned that a few drops of vinegar will soften white/yellow glue fairly rapidly.
Rex

Click to expand...

You did.

Rex R said:

little surprised that no one mentioned that a few drops of vinegar will soften white/yellow glue fairly rapidly.
Rex

Click to expand...

Didn't know that until you said it. Thanks. Learn something every day.

heres how I do it:

[video=youtube;Uol5AYTq0-g]https://www.youtube.com/watch?v=Uol5AYTq0-g&list=UU3builfBvFxj13D88qCUR5g&feature=share&index=10[/video]

I use the edge of a exacto knife and remove the glue like you remove the mold seam on a nose cone. Works very well.