Better fin fillets and finishing tips.

[Rocketguy13]

Hello to all who read this. I have had my Jr. HPR Cert with NAR for nearly a year, but I'm not very good at filleting and finishing fins. I have a few HPR rockets and I'm currently working on a NIKE Smoke 4" diam. all fiberglass from Madcow. I would appreciate any tips for fillets and for finishing fins on future rockets.

ON TOO FLYING!

[GRIFFIN]

Hello to all who read this. I have had my Jr. HPR Cert with NAR for nearly a year, but I'm not very good at filleting and finishing fins. I have a few HPR rockets and I'm currently working on a NIKE Smoke 4" diam. all fiberglass from Madcow. I would appreciate any tips for fillets and for finishing fins on future rockets.

ON TOO FLYING!

change your font, very hard to read.

[cbrarick]

Oy, I think he's asking about doing filets on a 4 inch rocket of some sort or another. He'd have great luck searching his question as this has been done ad naseum.

JMHO

[Rocketguy13]

Sorry about the font. Here's the message again-

Hello to all who read this. I have had my Jr. HPR Cert with NAR for nearly a year, but I'm not very good at filleting and finishing fins. I have a few HPR rockets and I'm currently working on a NIKE Smoke 4" diam. all fiberglass from Madcow. I would appreciate any tips for fillets and for finishing fins on future rockets.


I'm asking about techniques in general.

[DJDeadParrot]

First thing: don't use 5 minute epoxy for fillets.

Something I found really handy for smoothing out fillets on a 4" rocket with 4 fins was a scrap piece of BT2.14 to run along the fillet while the viscosity was still good and syrupy.

[Rocketguy13]

I never use 5 minute epoxy. I'll have to try the BT2.14 sometime. Fillets have always been my biggest problem during construction. Anything's a help at this point. Thanks for the tip.

[UPscaler]

I would use at least 30 minute epoxy for fillets, I would also fill it with colloidal silica so that it is peanut-buttery, mask off the fillets with blue edge lock painters tape, apply the fillets with a piece of PVC pipe, and as soon as the fillets are done (not after they dry) pull the tape off.


http://www.youtube.com/watch?v=snCVQYmwgQY



Braden

[COrocket]

If you use a good epoxy (such as West Systems or Aeropoxy) with a relatively good pot life, along with a filler, you should be fine.

What I do:

Then use a round filleting object, scratch the surface where the object contacts the body tube and fin. Put tape along the outside of the line (where you don't want any epoxy). I mix Aeropoxy with colloidal silica, until it is the consistency of peanut butter, maybe a little thinner. Use the round object to draw the fillets and make a smooth contour. Repeat for other fins, if you have the right consistency you can do all 4 fins at once. Let dry. Lightly sand once cured to make sure they are smooth.

I'd recommend downloading the instructions for one of the Wildman kits. A process very similar to the above is outlined, with the benefit of pictures. If you have the right glue and fillers, the process is pretty easy

[Lentamental]

Pulling the tape off as soon as you're done shaping the fillets is a really good tip. I didn't do that on my last build and it was a PITA to sand off the rough edge left where the tape pulled up.

[Le Aeronautical]

For most rockets the above ideas work. If you have something vital or expensive I recommend high shear glue. When doing tensile tests on composite samples you glue four fiberglass tabs to the sample, two on each end and front and back. Then you typically apply this high shear glue to make the fillet. It's very putty-like, like bondo, but a hell of a lot stronger. To make an easy fillet I always use the end of a popsicle stick and just run it down the full length of it. Works great! Plus you don't have to worry about that sucker ever getting ripped off, at least under any normal conditions.

[cjl]

I typically use some kind of laminating resin with enough colloidal silica to make it about the consistency of peanut butter. That allows you to shape all of the fillets at once, and they will be quite strong.

[Rocketguy13]

Thanks for the tips everyone. Some of these might push my budget (seeing as I can't get a job because I can't drive a car due to my age) but I'll see what I can do. Can anyone reccomend a good place to get the items you've reccomended? West Systems epoxy shouldn't be much trouble, but I have no idea where to get high shear glue or colloidal silica. Thanks again!

[Pantherjon]

US Composites has everything you should need..
I use their 'house' brand epoxy and have good results- don't overspend for West as I think it is overpriced, IMNSHO.I bought the gallon 'kit' of their 635 thin medium cure a while ago and still have quite a bit left- it is good stuff...West 406 Colloidal silica is there as well, the 6oz tub will last you a GOOD long time..

[skyspike1]

I think any of the common 2 part epoxies available from most hardware stores are sufficient for most HPR uses. The longer cure times, (45min) are better. If you don't have any disposable oral syringes for applying, a V shaped playing card works well for "pouring in" fillets, followed by smoothing over and shaping with a Q-tip wrapped in seran-wrap, or bending a playing card to appropriate U shape to drag/form fillets, clean off excess when "Tacked up", remove any tape and let dry before rotating assembly for next set. Good Luck!

[cwbullet]

I will second the US Composites. The thick is good for fillets.

[cjl]

US Composites has everything you should need..
I use their 'house' brand epoxy and have good results- don't overspend for West as I think it is overpriced, IMNSHO.I bought the gallon 'kit' of their 635 thin medium cure a while ago and still have quite a bit left- it is good stuff...West 406 Colloidal silica is there as well, the 6oz tub will last you a GOOD long time..

You get the six ounce tubs of colloidal silica? Those would last a good long time - I get the 1.7 ounce containers, and even then they last me quite a while. The 6 ounce tubs must be enormous.

[Le Aeronautical]

I also second, or third, or fourth, or whatever number we're at, US Composites. I think they also sell other fillers besides silica.

If you want to go the other route, a Google search will point you to a dozen different places: http://www.google.com/products/catal...d=0CGoQ8wIwAQ#