5 minute epoxy for fin roots?

Putting together this kit - 3" LOC cardboard tube with fiberglass fins. Normally I'd use rocketpoxy for everything, but hoping to speed things along. For complicated reasons (see below if you're really interested) I can't do what I'd usually do - glue all 4 fins at once with a fin guide. I'm going to do them one at a time. Since RP takes a solid day to dry, gluing one fin at a time is going to take ages. Now... normally I'd shy away from 5 minute epoxy for an HPR build, but I was thinking - if I just use it for the fin roots then do some solid internal and external fillets, I should be good, right? And this way I can knock out all 4 fins (at least the initial gluing) in a couple of hours instead of several days.

The longer "why":
Whoever cut the fin slots on this kit didn't cut them at exact 90 degree intervals. So instead of being 0/90/180/270, it's more like 0/90/181/273. So my Payload Bay-template-on-foamboard alignment tool is off by just a little bit. My solution is to glue one fin at a time using the alignment tool, then embiggen the other slots in it, so only one fin is held tightly. It's not perfect, but it should work.

"if I just use it for the fin roots then do some solid internal and external fillets, I should be good, right?"

yes

Why rush the it? Enjoy the build. This is a hobby.

For my L3 rocket I used West Systems 5 minute to glue the fin roots to the motor mount. Then I used West Systems 105/205 mixed with chopped carbon fiber to inject internal fillets. Rocket Poxy for external fillets. Held up to a N3300R so far...

crossfire said:

Why rush the it? Enjoy the build. This is a hobby.

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Good question. Because of the long cure time with Rocketpoxy, especially if I'm trying out something new, I'd be paranoid - at least somewhat - about things shifting or sliding or settling while the glue cures; I don't want to "babysit" the rocket for hours and hours, if that makes sense. Short of getting one of those fancy guillotine jigs, is there a good way to secure a fin against the mmt tube while it dries? That's mostly why I wanted a short cure- so I could know that it was solidly aligned and not going to slip half an hour later while I wasn't watching.

The only epoxy I use is five minute

I used 5 min on nearly all the cardboard rockets I built. Used some higher quality on fiberglass builds.

Chances are you will be fine until you have a hard landing. Depending on how hard, the b epoxy choice won't matter much.

some folks use masking tape to hold fins upright.
Rex

ActingLikeAKid said:

Good question. Because of the long cure time with Rocketpoxy, especially if I'm trying out something new, I'd be paranoid - at least somewhat - about things shifting or sliding or settling while the glue cures; I don't want to "babysit" the rocket for hours and hours, if that makes sense. Short of getting one of those fancy guillotine jigs, is there a good way to secure a fin against the mmt tube while it dries? That's mostly why I wanted a short cure- so I could know that it was solidly aligned and not going to slip half an hour later while I wasn't watching.

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Your right there. It is nice to tack fins in place knowing if you leave the room you won't come back to having them move.

"some folks use masking tape to hold fins upright."


And some do both. One to keep straight and the other to hold down tight.

Then tack it with five minute and use rocketpoxy for the rest of the fillet. My opinions. The jigs make it so much easier though.

The faster curing the epoxy is, the more brittle it is. I like to tack my fins in place with "CA in a couple of spots. Then go and do the fillets. I have never used RP, but the epoxy I use does not run so I can do all the fillets at the same time. I have read that if you let RP sit for 30 minutes that you can then do that also.

Update:
Got some 5 minute, glued fin on, waited. Was getting ready to put second fin on. Rocket fell over, first fin fell off. I know I was just gluing the root, mostly to hold the fins in place for some big strong fillets...but still. Pulled the fin out and I was able to scrape the epoxy off with my thumbnail.
Mixed up some rocket poxy, first fin is drying overnight. Patience is a virtue.

before you completely write off your 5 minute epoxy as being bad, try mixing say a 7g batch and see how long it takes to harden. I've had some mis-labeled epoxy in the past(BSI by another name), label said it was 30 minute when in fact it was 6 minute. turned out to very nice 6 minute epoxy...bit surprising when I was expecting a longer pot life. also room temperature makes a big difference in curing time.
Rex

David Schwantz said:

The faster curing the epoxy is, the more brittle it is.

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I used to go by this rule, and used (probably for no good reason) 30-minute epoxy for everything, but then one day I spent a good bit of time reading through the Bob Smith website and noticed this in the description of their 15-minute ("Mid-cure") epoxy (emphasis mine):

So, while they say that the 30-minute epoxy is strongest for gluing metal, glass, and a few other materials, they specifically call out 15-minute as most flexible. I don't know why this is so, but I assume they know the properties of their own products.

And so I purchased some 15-minute epoxy and plan to use that for most things, although I still keep 30-minute around in case I need to glue metal.

Disclaimer: for the LPR and small MPR stuff I do, 5 minute would no doubt be fine for everything. I do prefer having a bit more working time usually though.

The only 5 minute I've used is Loctite Heavy Duty, and that's served well when I've used it.

My L1 4" Patriot is still alive and kicking past it's intended use.

These days I use 39 minute on parts for the working time, and rocketpoxy or wood glue on fins

I have used BSI five minute epoxy and Great Planes 6 minute for tacking things. For tacking fin roots they’re great.
I’ve also built quite a few rockets using 15 minute and 30 minute BSI. Although my L3 rocket experience convinced me that I like Aeropoxy better for high performance rockets, I always keeps some BSI 5, 15, and 30 minute epoxy on hand, and for a quick build on the range those are what I would use. Use whatever you feel comfortable with. Rocket failures typically aren’t due to the epoxy but building techniques, skill, and inattention to detail.

neil_w said:

I used to go by this rule, and used (probably for no good reason) 30-minute epoxy for everything, but then one day I spent a good bit of time reading through the Bob Smith website and noticed this in the description of their 15-minute ("Mid-cure") epoxy (emphasis mine):

MID-CURE™ 15 min. epoxy is used in larger areas where more working time is needed. It is more water resistant and can be used as a substitute for QUIK-CURE™ in most applications. MID-CURE™ is our most flexible epoxy and is ideal for gluing to fiberglass surfaces. Allow 45 minutes before handling parts and 2 hours for full strength.
​

So, while they say that the 30-minute epoxy is strongest for gluing metal, glass, and a few other materials, they specifically call out 15-minute as most flexible. I don't know why this is so, but I assume they know the properties of their own products.

And so I purchased some 15-minute epoxy and plan to use that for most things, although I still keep 30-minute around in case I need to glue metal.

Disclaimer: for the LPR and small MPR stuff I do, 5 minute would no doubt be fine for everything. I do prefer having a bit more working time usually though.

​

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do they mean most flexible in terms of least brittle or do they mean most flexible as to its many uses?

solid_fuel said:

do they mean most flexible in terms of least brittle or do they mean most flexible as to its many uses?

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A valid question. I went back and looked at their directions:
To me that makes it fairly clear that they are talking about the physical property of the epoxy.

neil_w said:

A valid question. I went back and looked at their directions:

MID-CURE™ is our most flexible epoxy. This gives it superior bonding qualities in applications such as hardwood to fiberglass.
​

To me that makes it fairly clear that they are talking about the physical property of the epoxy.

​

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And if that doesn't make it clear enough, to really drive it home there is this part also: MID-CURE’S™ lack of brittleness allows it to form lasting bonds in areas subject to high vibration or stress.

neil_w said:

<snipped>

MID-CURE™ 15 min. epoxy is used in larger areas where more working time is needed. It is more water resistant and can be used as a substitute for QUIK-CURE™ in most applications. MID-CURE™ is our most flexible epoxy and is ideal for gluing to fiberglass surfaces. Allow 45 minutes before handling parts and 2 hours for full strength.
<snipped>​

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So, at least 45 minutes to handle '15 minute' epoxy, and 2 hours for full strength. I missed what part is 15 minutes? Here's what the website says:

"MID-CURE™ can be worked for about 10 minutes, with adhesion beginning after about 15 minutes."

So, not even a 15 minute working time. It's really a 10 minute epoxy for working time, and 2 hours for curing time. I don't think most of us would have correctly guessed what they meant by '15 minute epoxy'.

I've never heard that faster curing epoxy was more brittle? Here's what BS says about their '5 Minute':

"QUIK-CURE™ 5 min. epoxy cures to a slightly flexible consistency. This lack of brittleness allows it to form a lasting bond in areas subjected to high vibration or stress." ... "Items bonded with QUIK-CURE™ can be handled after 15 minutes. Full strength is reached in 1 hour."

So much for 5 minutes. My point is it's probably worth going back and doing another round of research on the epoxies we are using. I haven't looked at the System Three website in years, I really need to go back and make sure I remember everything correctly.


Tony

I have used Jb weld brand 5 min epoxy to attach fins and other bonds for rockets and around the house.

It sets quick but remains rubbery almost for a while, 24hrs it seems then becomes like a rock.

But for cardboard and wood TB2 wood glue is still my favorite for initial bonding. I have 2 MD fiberglass kits and I plan to tach the fins on with jigs, tape and CA glue or thin quick set epoxy then rocketpoxy or JB weld for fillets.

~John

I imagine one could add milled glass fibers to a 5-min epoxy to make it stronger, as well as increase its thixotropic (I believe that's the correct word) non-slumping properties.

I added milled fibers to 15-min epoxy for internal fillets and it worked great.

Curtis Enlow said:

I imagine one could add milled glass fibers to a 5-min epoxy to make it stronger, as well as increase its thixotropic (I believe that's the correct word) non-slumping properties.

I added milled fibers to 15-min epoxy for internal fillets and it worked great.

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Thinking about trying to mix those into a workable dispersion within the 5-min working time (more like 3) is giving me hives

Nytrunner said:

Thinking about trying to mix those into a workable dispersion within the 5-min working time (more like 3) is giving me hives

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Not wearing gloves while doing it gives me hives! LOL

That's why I like 15 min epoxy for small batch stuff.

Nytrunner said:

Thinking about trying to mix those into a workable dispersion within the 5-min working time (more like 3) is giving me hives

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Measure out the resin and hardener separately. Then add the amendments to the hardener and resin until each is the consistency you want in the end. This way you’re not using up the working time.
You can even add a tiny amount of dye to one of them (but not both).
Then, when you’re ready to use them, mix the two parts together. The tiny amount of pigment lets you see any unmixed resin or hardener.

Wouldn't adding a different dye to each allow you to more easily differentiate / remediate?

For instance, the human eye is extremely good at telling greens apart, so yellow in one and blue in the other should help you know at each instant where the pockets of each remnant are.

Just an idle Saturday thought.

dhbarr said:

Wouldn't adding a different dye to each allow you to more easily differentiate / remediate?

For instance, the human eye is extremely good at telling greens apart, so yellow in one and blue in the other should help you know at each instant where the pockets of each remnant are.

Just an idle Saturday thought.

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Yes, having contrasting colors would make it even easier. I mentioned only adding dye to one part assuming a single dye color. One-half drop of black contrasts nicely with clear epoxy resin with a white amendment such as West 404.

If ya mix for 1 minute consistently , your glue will always be thoroughly mixed.Regardless of color.[unless mixing large quantities then 2 minutes]

blackjack2564 said:

If ya mix for 1 minute consistently , your glue will always be thoroughly mixed.Regardless of color.[unless mixing large quantities then 2 minutes]

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If you've done it hundreds of times you'll know that both in your head and your gut. If this is your eighth go, a little color might help the ol' gut even though your head is fully convinced ^_^

If I do any epoxy in my rocket classes I think I'll pre-dye all the A's & B's. Should help me inspect at all phases.