fin removal

[jraice]

I have a thor (3 sets of two fins, similar to PML endeavor) and it has a loose aft fin. Probably could hold up to small I's and J's but I plan on using it for dual deploy soon and that fin is going to come right off. It is hard to tell what the damage is, the fillet is cracked but from the way it moves it feels like it has lost its bond to the motor mount tube. How do you recommend removing it? Elbow grease seems like it would work but I dont want to mess up the tubing to much, also, after getting it out, how do you remove all of the fillet stuck to the fin? Thanks...P PS: I have heard of heating the epoxy but this wont fit in any oven I have and I cant really see it just coming out after heating with a hair drying...

 

[BobCox]

Try a heat gun. It's like a hair dryer on steroids. Some come with a narrow nozzle so you can direct the heat to a small area.

Be careful with these -- they can get REALLY hot. My father-in-law routinely uses his to light his charcoal grill. Almost as fast as lighter fluid without the nasty aftertaste.

 

[Rocket Guy 1317]

If it was G10 you could just give it a good hard hit with the palm of your hand the break the epoxy. With my PML Phobos one of my fins came loose so I just gave it a good hit it broke the epoxy fillet I removed the and re-epoxyied it in place. But I think the Thor has Baltic birch fins so I don't know if you could do that with those kind of fins.

 

[jraice]

Well I guess I will start out with trying to break it, it is pretty loose... might try to peel some of the kraft under the fillet so the fillets are not holding the fin on. EDIT: Well I used some muscle and got one side of the fillet completly cracked, the other side wont break at all, any tips? I wasnt very worried about breaking the fin (would rather not but I could always get my dad to make another one if I pay for the wood), I was more worried about breaking a fin or the joint of the fin I was holding onto when breaking the loose fin... thanks

 

[dbarrym]

If the fin is not completely loose, it might be better to drill some holes along the fin and through the fillets and use a glue syringe to inject some medium cure epoxy into the fin/MMT joint; tilt the rocket fore and aft and wiggle the fin to get the epoxy to flow around and soak into the joint and set the rocket down flat with the damaged fun upright. After that has set up, carefully push down on the body tube around the fin and work some epoxy around/under the fin fillets and let cure. You can leave it as is or refinish.

You can get single-use plastic syringes at better hardware or hobby/craft stores. Or do an online search. I always keep a few on hand for this type of repair.

IMHO, if you properly prepped the fins and MMT tubes during construction (sanded with 80 grit or so and cleaned the surfaces with solvent), you should be breaking the fin or body/MMT tubes before popping the glue joints...something to consider as you move up to higher power motors.

Hope the repair goes well -

barry

 

[cjl]

Originally posted by dbarrym

IMHO, if you properly prepped the fins and MMT tubes during construction (sanded with 80 grit or so and cleaned the surfaces with solvent), you should be breaking the fin or body/MMT tubes before popping the glue joints...something to consider as you move up to higher power motors.

barry

I would have to agree, Barry. I have several high power rockets, and my only one that I really designed to take bigger motors feels like I could actually snap the (1/8" G10) fin off before it would break the glue. I have only flexed it before (nowhere near breaking), but when I do, there is no flex at all in the epoxy or body tube, there is no creaking of epoxy, the only thing that flexes is the fin itself.

 

[firemanup]

For the externals i've used a Dremel with the barrell head.. goes right down and through them.. then you have to work it from there...

Agree with the above if a good smack takes em off i wouldn't expect em to last through many landings...

 

[cls]

Barrry's right, but only for plywood. I have never got G10 to bond that well, with any kind of glue. that's one of the reasons I am on an anti-G10 campaign.

 

[jraice]

Broke it off, thanks for the tips. Any tips for getting the fillets off the fin? Plan on reattaching it today.

 

[dbarrym]

Hey Cliff- I've been using G-10 as well as FG and CF sheet for many years in my models (RC jets, giant scale aerobats and now HPR) and the key to a failure-proof bond is proper surface prep and adhesives. Hobby shop epoxy (5, 12, or 30 minute) is not the best... I use the hobby shop stuff only for tack bonds and quick repairs and Hysol, AnchorBond, or West Systems resins for the actual gluing. You really need to rough up the G-10 to provide a good mechanical bond, but the better quality resins actually create a further chemical bond (unlike the hobby shop stuff).

JRaice, why break off the fillet? Unless it has a really poor bond on the fin, just rough up the exposed fin surface and re-bond the fin, leaving the fillet on will make refinishing easier.

If you really need to take the fillet off, use a dremel with a sanding drum...better yet, use a scuff board or sanding block with 100 or 150 grit paper on it. Use some masking tape above the glue line to protect the finish on the fin above the point you want to sand to. Just my $.02....

Barry

 

[cjl]

Cliff - mine are attached with some good (west systems and Devcon 14320) epoxy. If you use these rather than basic "hobby shop" epoxy, as well as scuffing up the surface (I used 80 grit) well before bonding, G10 sticks just fine. As I said before, it honestly feels like the 1/8" G10 would break before the glue would on my rocket.

 

[jraice]

Well the rocket was my first HPR and is trashed up (needs a new paint job) and the fin doesnt seem to hit the motor tube very well because the fillet and the epoxy on the tube interfere.

 

[hartlch]

This thread caught my eye since I'm in the middle of repairing a fin on my PML Endeavour. It came down on the drogue only and cracked one of the lower G10 fins right along the top of the fillet. There was no damage to the fillets at all. The G10 fins and Quantum tube were roughed up with 80 grit and the glue was Aeropoxy structural adhesive (ES6279). I added a little cotton flocking to the epoxy to thicken it up too.

From the comments in various threads about how difficult it is to get good bonds to G10 and Quantum tube, I didn't expect to have this much work to get the broken fin out...

I had considered beefing up the joints with some glass cloth, but now I don't think I need to worry about it.

Chuck

 

[jraice]

I think the QT is more of a problem, G10 fins on subsonic rockets should be fine with hobby grade fillets and good bond to the motor tube. For my CF rocket (near minimum diameter) the motor tube (phenolic) will be extremely roughed up so the 1/8" G10 fins get a very good bond, the fins will also be very roughed up and possibly have some small holes drilled through the fin just above the part touching the tubes slot (thickened epoxy fillet wont run into the holes but if they are just above the tube slot then the thin 5 minute epoxy will seap into the holes when tacking the fins on. Milled fiber will be added to the 2 hour epoxy for fillets and some 3oz glass will go from half way up the fin, over the body tube, and half way up the opposite fin. But the real fin strength will come from the thin epoxy injected into the fin can completly filling the section between the two rings (where the fins are) with epoxy, like foaming the fin section but there is so little room thin epoxy is being used.

 

[dbarrym]

Sounds like a good plan, jraice.

Hartlch, Quantum is pretty much the exception, I just make sure I scuff it up really well using coarse Permagrit tools to try to get a good mechanical bond and clean well with alcohol or acetone. I also use Aeropoxy (it's Hysol 9462, same stuff as BVM Aeropoxy). My Tethys (with 3.9" quantum tube) flat spun in after the main chute hung up on a fin and scratched up the paint but did not loosen a fin or crack a fillet...it has since flown on a J280, a J500 (EX load - a hot one!), and a J350 with no damage.

Barry

 

[robfire820]

I have also cracked a fin on my Endeavor, luckily I was able to rebuild it using, epoxy and kevlar strips. and then re-inforced the rest of the lower fins the same way. Now it just needs a new paint job. It looks like its been flown a time or 2.

 

[hartlch]

Barry,

Yep, I don't have any problem with the Quantum. I was just giving an example to illustrate what a couple posts above were saying about proper preparation and quality epoxy. Especially for "difficult" surfaces like Quantum and, to a lesser extent, G10.

My case is kind of the extreme limit of what cjl said in one of his posts, except I -did- bend the fin to the breaking point. The Aeropoxy was still solidly bonded to the Quantum tube and the G10 fin stub.

BTW, the Hysol products looked interesting to me too. I like the dispenser gun looks like it would be handy for bigger projects.

 

[jraice]

Well the thor is looking good, fin is in place and the fillet is dried, gave all 6 fins a bevel with a sander and it looks nice... another question about fin removal, is it possible to remove a 54mm acme fin can from a QT tube somehow? It had three "lines" of tape, one at the bottom, top and middle for a better fit... rocket is trashed and I have a 54mm phenolic tube that I was going to use to make a new bird...