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Different Epoxy for Different purpose??

Posted: Sat Mar 18, 2017 5:15 pm
by NewtonsLaws
Hi New to HPR.
Aiming for L1 cert next rocket in April.

Was told to use JB Weld for attaching motor retainer to motor mount tube for temperature.
But not to use JB Weld for fillets as too brittle.

Ok got that.

BUT should I use JB Weld for
centring rings to motor mount tube?
centring rings to body tube?
shock cord to motor tube?

Or stick with fillet epoxy?

and is 5 min epoxy ok or do I need to use 15min epoxy?

Re: Different Epoxy for Different purpose??

Posted: Sat Mar 18, 2017 6:27 pm
by SpaceManMat
Really only the retainer needs JB, even then for a 38mm motor any decent expoxy would probably do.

Some people do use JB for fin fillets, but only normally when they have a black fibreglass rocket that they don't want to paint.

Either 5 or 15 minute expoxy is fine it more about what you are comfortable using.

Re: Different Epoxy for Different purpose??

Posted: Sat Mar 18, 2017 6:43 pm
by OverTheTop
Hmm. Glue threads are always contentious. Many opinions.

Data sheet is king. Know the specs and what you want to achieve.

Having said that, there are rules of thumb.

Personally I would use JB for anything in contact with the motor casing. Its higher temperature rating helps it keep its specifications under the increased temperature there.

I use West Systems 105/206 (slow set) for everything else. It is what I have so it is what I use. Never let me down along the way to L3 or Mach 1.8 yet. There are some other epoxies that are slightly stronger but harder to source, so I stick with WS (no pun intended). It is a bit slow sometimes, but working the joint in hot weather with faster hardeners can be stressful.

Generally the quicker the set the less strength the joint has. It is a bit of a generalisation, but generally right. As I said earlier, the data sheet is king in this area. Remember you need to mix them correctly to achieve the specifications. I mix by weight exclusively.

This is only one opinion :)

Re: Different Epoxy for Different purpose??

Posted: Sun Mar 19, 2017 10:58 am
by Kryten
I concur with the comments by OTT.
5 minute epoxy will work, but generally speaking, epoxies with longer set times are usually better - primarily due to the different hardener (the part "B") and the resulting structure of the cross-linked polymer.
I believe 5 minute Araldite becomes more brittle over time, so I would avoid it (although I did use it in one of my mid-power rockets for convenience)

Re: Different Epoxy for Different purpose??

Posted: Sun Mar 19, 2017 11:46 am
by OverTheTop
5 minute Araldite

Avoid it like the plague...

Re: Different Epoxy for Different purpose??

Posted: Mon Mar 20, 2017 5:37 pm
by NewtonsLaws
Thanks everyone!

I was looking at Loctite epoxy spec sheet.
it seems to have a higher termparater rating (150 deg C) and strength than Selleys araldite.

Any thoughts?

And where does one get this other magic stuff?
It does not seem to be in the common bunnings etc.

Re: Different Epoxy for Different purpose??

Posted: Mon Mar 20, 2017 8:44 pm
by OverTheTop
I usually buy West Systems at Carbatec ( but they don't have a large range of hardeners or sizes. They do suit what I buy though. Probably worth a look.

You local boat-building place can probably help too, although if you mention the word "marine" the price will likely go up :) . Make sure you go through the data before purchasing.

Just Google and you should be able to find it.

JB can be purchased at Australian Rocketry and many other places.

Forgot to mention. You might be able to get some epoxy donated from some HPR flier(s) that have some to spare, if you don't need much.

Re: Different Epoxy for Different purpose??

Posted: Fri Mar 31, 2017 8:52 am
by Lamp
For an L1 rocket (unless you are doing a glass tip to tip or rolling your own tube) all you really need is "hobby" epoxy like BSI. Blake sells this in the Aus rocketry shop. I tend to use either the 15 min or 30 min stuff to make sure I have enough working time.

For higher strength requirements I also use West Systems but typically with 205 fast hardener (about 30min working time), generally with chopped CF (injected internal fillets) or Wests micro fibre filler (for external fin fillets).

JB weld is great for anything attached to the motor mount tube (retainer, CR) but to be honest, you could get away with not using it. A small HPR motor will not get hot enough for long enough for you to really need it...but having said that, I always use it for these applications :wink:

Re: Different Epoxy for Different purpose??

Posted: Mon Jul 03, 2017 5:29 pm
by joeman
Continuing this thread....(might help others)
RE: 4" Katana
I've just purchased some J-B Weld for the gluing of the fins (root of fins) to the Motor Mount. This seems like the most sensible decision based on the knowledge that the motor mount will increase in temperature some what. It should also be relatively easy to apply as well.

External Fillets
My decision on the external fillets is West Systems - 105/206/403. That seems like a widely used combination and I like the idea of the 'peanut butter consistency' ... to make the creation of the fillets easier.

Internal Fillets
For the internal Fillets, I was originally toying with idea of using just 24hr Araldite. But now I'm thinking I should just use West Systems instead.
In terms of creation of fillets, I wouldn't expect either to be harder to create.

So then it comes down to strength...It looks like there are a lot of different ways to 'measure' the strength of a material.... and it isn't just the strength of material, but the adhesive properties, the temperature of use, etc. Lap Shear strength seems to be a common way to measure the strength...but it is hard to validate and come to any sensible conclusion.

26MPa at 40degrees for Selleys 24hr Araldite - Bonding to Aluminium.
2346PSI (~17MPa) At room temp (so assume 25 degrees) for West Systems bonding to G10

I know that Araldite strength drops off considerably above 100 degrees C. Does that makes me wonder if West Systems 105/206 retains greater strength as temperatures increase. Searched in vain for something to help me compare to Araldite, but nothing solid.
Question: Does anyone have any information on West Systems strength at various temperatures?

Any other thoughts?


p.s. I'm also aware that the surface preparation is KEY to the success of the joint and may significantly affect performance.

Re: Different Epoxy for Different purpose??

Posted: Mon Jul 03, 2017 7:50 pm
by OverTheTop

Re: Different Epoxy for Different purpose??

Posted: Tue Jul 04, 2017 2:06 pm
by drew
I figure it's worth chiming in as it seems everyone has their own preferred epoxy systems. For me, I routinely use 4 different types of adhesives for my builds. This has recently changed as well so it's good to document when changes occur.

1. JB Weld - for Motor Retainers/bonding metal to a motor mount. That's ALL I use it for. Motor retainers.
2. Araldite (5 minute) - I use this for tacking fins on as it's fast.
3. Epiglue - for fin fillets and any internal glue work. The consistency is so thick runs aren't a worry. Great stuff.
4. Araldite K3600 - I use this for rolling airframes, making fin stock, and doing layups on fins. Incredibly low viscosity so it's great for this type of work.

Historically I used Proline 4500 for fillets and internal work but I went through two quart sets and wanted to go local. I've got some RocketPoxy too but I've never really taken to it. I still have a large amount of Wests Systems but I prefer to use the Araldite K3600 kit given its superior capabilities when compared to Wests.

Re: Different Epoxy for Different purpose??

Posted: Tue Jul 04, 2017 10:24 pm
by Oldboy
Proline 4500 for me ,fillets and mechanical bonds (had a rocket driven over by DFWM agricultural vehicle last season ,fillets and bond held)
JB weld for retainer bonding ,and that's all it's good for ,my humble opinion.
And yeh as Drew said

Re: Different Epoxy for Different purpose??

Posted: Sun Aug 06, 2017 3:33 pm
by joeman
Thread is a bit old, but thought I'd just share a small bit about my experiences.

I've been practicing using WS 105/206/403 to help produce the optimum 'mix' for the external fillets. I've used a sieve to filter out the clumps of 403 and I very carefully stir in the 403, being careful not to introduce air into the mix. (Cavitation). So the process of making a good batch takes a while, but 206 is good for up to about 25 mins from memory.

So far, I've had good results with doweling/sandpaper to get the smooth finish. i.e. little or no craters and a good profile.

I've been practicing the process and intend on doing a bit more practicing before I do the real thing. I think have a few practice runs is a very good idea if you don't do it all the time.

This is just what I've found out so far. Still learning :-)



Re: Different Epoxy for Different purpose??

Posted: Tue Aug 08, 2017 10:12 pm
by joeman
I've actually got a follow on question.

I'm up to the internal fillet stage and I'm still finalising the exact strategy/steps. Will definitely be using a syringe and West Systems.

I've already done trial internal fillets on a 'test fin' in an artificial setting, where I could easily put some wooden stops to stop the 105/206 from spilling over the ends of the pretend fins.

Now, with the real thing, access is a lot more constrained, so I'm probably going to push up 5 min epoxy soaked 'stop' (a short stub of rope)...and let it dry there. This to be done at both end of the fins. Then was going to add 105/206/403 (with a viscosity approaching mayonnaise) since I don't really trust the stub to stop pure 105/206 from flowing around. I've seen how the stuff runs. Now I'm pretty sure the 105/206/403 can be made sufficiently runny to fill all the gaps (including the scoring I did of the fins) AND cover as much of the fins/motor mount WITHOUT seeping past the 'block'. i.e. I'm aware that I need to cover as much area as possible to get maximum adhesion. And I have no reason to believe the 403 will reduce the strength of the final epoxy mix.

I don't see much mention by others of the use of 403 in Internal fillets and I must say that makes me wonder why. It seems like an obvious choice. I've already confirmed I can pretty easily push a mayonnaise consistency epoxy mix through tube and syringe.

Can anyone think possibly why?



Re: Different Epoxy for Different purpose??

Posted: Tue Aug 08, 2017 11:06 pm
by SpaceManMat
Well as previously mentioned people have many differing opinions...

Personally I would not use west systems because of the viscosity. It's my understanding that anything you add to the epoxy will weaken it to some degree. To me west is more practical for rolling tubes or doing tip to tip.

Generally an internal fillet is not terribly critical so I would normally just be going with a cheap bob smith 15 min epoxy. If I wanted high strength fillet I would go with epiglue.