Fillets what to use?

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djpaulys

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What brands of epoxy putty do you use
I doing some testing on loctite and it does not seem to spread too good
Just looking for something I could buy locally
It's going on a all fiberglass madcow tomach
What can you guys recommend


IJEEPIN
Paul Sandyck
Membership Officer
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I think most of us don't use epoxy puttys, we use epoxy thickened with fumed silica, phenolic microballoons or such, the epoxies are typically Rocketpoxy, Aeropoxy products, West Systems products, US Composites 635 products, or hobby shop (Bob Smith or Red Baron, commonly sold as 5, 15, 20 min finishing, and 30 min, they may be hobby shop branded) epoxy thickened with the above mentioned items. For a Madcow Tomach I would recommend any of the first 4 name brands listed.
 
Tomach is an MD. You need something with heat resistance. Proline 4500 or JBWeld would be ideal.
 
For a smooth, cream-like epoxy, use MarineTex. I have no idea if it is available in Ohio, but it is at marine stores in the Seattle area. It spreads easy. Stays where you leave it.
 
JB Weld works great.
Make sure to sand the bonding area with 40 grit sand paper and wash it with soap and water to remove any residual mold release and give it a rough bondable surface.

8491C748-BD6B-4BA6-A99E-A6A5546D8904.png
 
How big should they be I was testing with the end of Popsicle stick is that big enough or something else


IJEEPIN
Paul Sandyck
Membership Officer
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I--I--L--OIIIIIIIO-
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JB Weld works great.
Make sure to sand the bonding area with 40 grit sand paper and wash it with soap and water to remove any residual mold release and give it a rough bondable surface.

8491C748-BD6B-4BA6-A99E-A6A5546D8904.png

Do you have a picture with the tape off and what did you use to make your fillets stick finger?



IJEEPIN
Paul Sandyck
Membership Officer
/|_|,[______],
I--I--L--OIIIIIIIO-
( )_) ( )_)--o--)_)
 
I want to reiterate, because there is a lot of bad advice out there on epoxy all over this forum:

Use a high temp Epoxy, like proline 4500 or JB Weld. You're glueing the fins to a tube that is in direct contact with the motor case. Sure, we do that in every rocket, but not as the only support.

Mark a small bit of 1" pvc pipe on the end with a TON of sharpie marker. Rub the pipe on the fins and body to mark a line where the tape goes. then Tape off much like BayouRat did. Use a popsicle stick to lay the epoxy into the area, then pull the PVC down the fillet. Clean the pipe off with some alcohol/acetone/etc, and do the opposite fillet. I do two at a time so I can just leave it to set.

1" pipe leaves a pretty fat fillet. On an MD like this, it'd be appropriate.

I typically put the tape over the sharpie marks, so you can see them here...
9020081853_77efe789b6_b.jpg
 
I just use a tongue depressor type craft stick. I bought a pack of 100 at Walmart for about $5

Here is the picture without the tape.

C806A2FD-FA0F-4884-B605-4A43857707F8.jpg
 
One thing to remember; on RocketPoxy, NEVER use any fillers or additives. That is straight from John Olevich himself (the maker of RocketPoxy).

Adrian
 
Because it's MD and you do not have the luxury of TTW fin mounting you should be more diligent that would would otherwise be in both the type of epoxy and the technique. There are several threads discussing bonding techniques using epoxy but in a nutshell here is what I used and did for my 54mm MD carbon fiber Tomach. I would consider it overkill, considering that the majority of flights will not exceed Mach 1.3 but I want it to last.

The fins are surface mount so you should increase the size of the bonding area, this can be done by taking a file and using the edge to file groves into the root edge of the fin. You also want to make sure that the tub area is well scuffed up, I use 80 grit but you can also use the same technique you used on the fins, on the body...you just need to be careful. Bottom line is preparation of the work surfaces is just as important as the type of glue/adhesive. Before you stick the fins on you should also rough up the fins running in the same direction as the body. This will give the epoxy and fillets to adhere to.

For the root I used Aeropoxy ES6209 structural adhesive, without any fillers.

For the fillet I used Proline 4500 for the additional heat resistance although I am not likely to ever realize any appreciable difference in thermal gains with this rocket. I could of just as easily used the same ES6209 or many other epoxies.

For an added layer of strength I also scuffed the entire fincan area and applied a single layer of carbon fiber 3K 3x3 twill cloth with Aeropoxy 2032 laminating epoxy then put it under vacuum for 12 hours, removed trimmed and left to cure.

Once it was cured I added Proline 4500 on the leading edges of the fins, again not required but it gave it a more serious finished look.

View attachment 269202
 
to pass certification, motor case temps can be up to 300 degrees C I believe. Here's the data sheets on ES6209 and Rocketpoxy. Granted you will not likely be at the motor's peak temp with the fins being up the body so much....but why tempt fate?

20264190052_0556ef7395_b.jpg
 
to pass certification, motor case temps can be up to 300 degrees C I believe. Here's the data sheets on ES6209 and Rocketpoxy. Granted you will not likely be at the motor's peak temp with the fins being up the body so much....but why tempt fate?

20264190052_0556ef7395_b.jpg

Dave has a good point, so I should qualify my statement of overkill. Combined with everything else I did it would be overkill, but I am a fan of overkill anyway. But that topic is another conversation.
 
Lol. After the atomic war three things will survive. Cockroaches, chuck Norris, and your fincan :)
 
I want to reiterate, because there is a lot of bad advice out there on epoxy all over this forum:

Use a high temp Epoxy, like proline 4500 or JB Weld. You're glueing the fins to a tube that is in direct contact with the motor case. Sure, we do that in every rocket, but not as the only support.

So based on this, my 4" minimum diameter that I flew to 20k on a N should have not worked since I used U.S. composite standard thin epoxy? Rocket did Mach 1.75. The 3" I built and flew to 15k on a long burn L should have failed too....
 
Flew them more than once? It may work, but it's not the best to use, so if you have a choice, why use something less than ideal?
 
So based on this, my 4" minimum diameter that I flew to 20k on a N should have not worked since I used U.S. composite standard thin epoxy? Rocket did Mach 1.75. The 3" I built and flew to 15k on a long burn L should have failed too....

I all has to do with the amount of heat transferred to the epoxy joint.
 
Tomach is an MD. You need something with heat resistance. Proline 4500 or JBWeld would be ideal.


I've used JB Weld for filets with great success. It's very sandable. The only disadvantage is the cost, as it's fairly expensive.
 
The less epoxy I have sitting around getting old the better. So I just thicken laminating resin with milled glass.

HTR 212 laminating resin thickened with milled fiberglass. 2 parts epoxy to 1 part fiberglass gives you a nice non-chunky paste. I use a 3/4 inch dowel on 3 and 4 inch MD airframes for shaping. I do this then fill any shape inconsistencies with HTR 212 mixed with west systems 407 fairing filler.

Is high temp 500F epoxy necessary when your filament wound airframe has a Tg at 260F? I'd say no, definitely not. It's important to match the capabilities of your components.
 
I tested jb weld and seems to work good plus I had it laying around
I will let you guys know how it turns out
Going to do a build thread on this one


IJEEPIN
Paul Sandyck
Membership Officer
/|_|,[______],
I--I--L--OIIIIIIIO-
( )_) ( )_)--o--)_)
 
JB weld comes in big tubes at ACE for just a smidge more $ than the small tubes.
 
I've used JB Weld for filets with great success. It's very sandable. The only disadvantage is the cost, as it's fairly expensive.

Try pricing Cotronics Duralco 4525IP https://www.cotronics.com/vo/cotr/pdf/4525.pdf Short self life too. You'll stick with J & B. To bad J & B can't be had in bulk tubs.

I've done fin fillets with 4525 neat (no fillers) and it turned out fine. Have two L3 capable rockets I used it liberally on but I won't again because of the cost.

I used to like PowerPoxy Weld for fillets but it went out of production and I used up my last of it. Very strong albeit a little heavy. Kurt
 
I used Aeropoxy 3660 on a 54mm fincan I have flown 3 times. Mach 1.8, 2.7, and 2.96 with nothing other than paint loss. No need for fancy expensive epoxy for 99.99% of MD flights
 
For small rockets I might use JB Weld for fillets.

For 54 mm and up I generally use Aeropoxy 3660 with Kevlar pulp amendment. I have used Proline laminating epoxy in the same fashion. These are not very sand able due to the Kevlar so then you use epoxy filler over those for cosmetics. I like Superfil for this.
 
Flew them more than once? It may work, but it's not the best to use, so if you have a choice, why use something less than ideal?

Several times actually, all on long burn motors. I think Kyle used west systems for his minimum diameter rocket he flew on the L2050 at airfest.
 
I want to reiterate, because there is a lot of bad advice out there on epoxy all over this forum:

Use a high temp Epoxy, like proline 4500 or JB Weld. You're glueing the fins to a tube that is in direct contact with the motor case. Sure, we do that in every rocket, but not as the only support.

Mark a small bit of 1" pvc pipe on the end with a TON of sharpie marker. Rub the pipe on the fins and body to mark a line where the tape goes. then Tape off much like BayouRat did. Use a popsicle stick to lay the epoxy into the area, then pull the PVC down the fillet. Clean the pipe off with some alcohol/acetone/etc, and do the opposite fillet. I do two at a time so I can just leave it to set.

1" pipe leaves a pretty fat fillet. On an MD like this, it'd be appropriate.

I typically put the tape over the sharpie marks, so you can see them here...
9020081853_77efe789b6_b.jpg
I'm going with this technique on my next built. I have been using my finger to make fillets and although not bad, they still come out a little uneven with thick seams that need lots of sanding to blend them in properly.
 
The sooner you can pull the tape, the smaller the edge will be.
 
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