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tOD

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I'm building a Mach1 Messier65 (65 mm airframe, 54mm motor mount) I'm going to do fin pockets for the first time. I'm trying to decide if I need a high temp epoxy like Proline, or if RocketPoxy would be OK. I also have some West that I thought would be good with a little chopped carbon fiber. I don't anticipate flying any long burn or high thrust motors. I'll probably bond the retainer on with JB Weld as I usually do.
Anyone care to offer some suggestions?
PXL_20210108_195155850.jpg
 

Jee3300R

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I’d use Rocketpoxy for the for the fins just because it’s least messy. The mmt doesn’t get too hot so most epoxies will be just fine for the CR’s and fin tabs.
 

OverTheTop

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No special epoxy needed. I normally use West System 105/206. I add microballoons for the fillets as it makes them easier to sand.
 

G_T

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I'd not use West Systems anywhere near a motor mount. The Tg (glass transition temperature) is way too low and will be exceeded every single motor burn. That greatly softens the epoxy. Heck, on a really hot sunny day with sun exposure you can exceed its rather pathetic Tg. Use something else. JB Weld for instance if you want something readily available in any hardware store, though it is not the cheapest solution. It can take some heat.

Gerald
 

jd2cylman

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I'd not use West Systems anywhere near a motor mount. The Tg (glass transition temperature) is way too low and will be exceeded every single motor burn. That greatly softens the epoxy. Heck, on a really hot sunny day with sun exposure you can exceed its rather pathetic Tg. Use something else. JB Weld for instance if you want something readily available in any hardware store, though it is not the cheapest solution. It can take some heat.

Gerald
Almost all of my motor mounts have been installed using West Systems injected and mixed with chopped carbon fibers. Holds up for me so far for N motors (but I've not tried 17 second burns...)... :dontknow:
 

tOD

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Almost all of my motor mounts have been installed using West Systems injected and mixed with chopped carbon fibers. Holds up for me so far for N motors (but I've not tried 17 second burns...)... :dontknow:
I have a couple of rockets that used injected West/ chopped fiber as per some build instructions I've read. Limited flights, but no apparent problems so far. I was considering that the viscosity might be easier to work with to flow it into the fin slots, they're 3/32". I'm going to order a new RocketPoxy kit today and just go with that. This project will probably never fly on anything larger than a small "K". Don't usually have access to a field that'll handle bigger.
 

OverTheTop

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I'd not use West Systems anywhere near a motor mount. The Tg (glass transition temperature) is way too low and will be exceeded every single motor burn. That greatly softens the epoxy. Heck, on a really hot sunny day with sun exposure you can exceed its rather pathetic Tg. Use something else. JB Weld for instance if you want something readily available in any hardware store, though it is not the cheapest solution. It can take some heat.
IMHO you are being too conservative. You are, of course, entitled to not use it if you want. I have used West Systems extensively on all my rockets. Never had a problem, and that includes MD rockets significant velocities, without tip-tip reinforcing. Just WS for the jointing and filleting. The list of flown motors on rockets just using WS includes N1100 and O3400.
 

JoePfeiffer

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I'd not use West Systems anywhere near a motor mount. The Tg (glass transition temperature) is way too low and will be exceeded every single motor burn. That greatly softens the epoxy. Heck, on a really hot sunny day with sun exposure you can exceed its rather pathetic Tg. Use something else. JB Weld for instance if you want something readily available in any hardware store, though it is not the cheapest solution. It can take some heat.

Gerald
In spite of its Tg of 142F, I've never seen it noticeably soften in a New Mexico summer. I 've never seen Tg quoted for the fiberglass we use, but it seems unlikely to be a lot higher and it's right up against the casing.
 

G_T

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Assuming you are using the fast hardener that's what it gets to, properly mixed right ratio etc. Other hardeners are lower. Anyway, look at the heat defletion temperature values. You might find them interesting.


Now if you want the ability to warm it up with a hair dryer, apply steady pressure, and slowly bend your fins back into alignment, go for it! I've used that method for fixing warps in parts made with West.

Just because you can usually get away with using something, doesn't mean it is really a good choice for the job. I wouldn't use it for surface mounted fins for instance on MD rockets. IF you are through-mounted, then the fin stability is much greater and likely you would never notice any issues. But I'd stay under M2.

I have experience with a variety of epoxy systems, some suitable for aerospace and some not. West is a great epoxy for working on wooden boats. And I've used it a lot, probably gallons by now, even for things like ebay sled glassing. It is available and convenient, but I recommend using something more suited to the job if it is going to get exposed to heat. That's just basic engineering.

Often you can use an inferior material if more of it is thrown at the problem or if it only has to work once.

Do what you want of course! I didn't mean to step on anyone's toes. But we have a lot of beginners here who will never have heard of Tg and don't know that various epoxy systems have different properties to suit their intended purposes.

Gerald
 

tOD

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I decided to use RocketPoxy. Here's the first two fins attached and waiting to cure before doing the two on the other side.
I picked up this method from a Badass Rocketry build video. Seemed ideal for this rocketPXL_20210122_143613372.jpgPXL_20210117_190819958.jpg
 

OverTheTop

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...but I recommend using something more suited to the job if it is going to get exposed to heat. That's just basic engineering.
Correct about using something suited for the job. Basic engineering is creating something that is "fit for purpose". Based on my experience, with flights up to M2.14, West Systems has given me no problems. There are "better" epoxies out there and they should be used when necessary. Otherwise they are technically considered "over-engineered" ;).

Yes, reading the data sheet and comparing based on actual data is is a must. There are some surprises out there and if you don't read the data sheets you must might be bitten by unexpected outcomes.
 

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