Epoxy inside airframe but 3 CR's along MMT

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Pyropetepete

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So I'm needing to now mount my MMT assembly into the airframe.

54 mm MMT
3 CR's
4" Blue Tube 2.0 airframe.

Have 1 CR at the far end, 1 just above fin tip mount point and then 1 will be at the aft (yet to fit as foaming the void in the can).

So doing a ring of epoxy on the 1st no problem using a stick to get it down in there. Then how do I get this 2nd middle ring as all access is blocked.

I will be using the expanding foam in the fin can if that helps.

Was thinking of using 15 min epoxy here. Giving me more work time.

Apply a thick ring inside the tube for the forward ring, slide MMT in until 1st is in past fun slots. Use a syringe to inject a band/bead/ring of epoxy and then push the MMT into final location. Stand the booster in the launch position so epoxy can flow back down and make "natural fillet" on the 2nd ring. Using IPA and finger inside the tube for the 1st to make make clean good fillet.

Confuse big time here. Never done a MMT with 3 rings before.




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what I've done is to put a ring of epoxy just past the forward end of the slots and slide the assy. into place. or if the forward ring is a lot further north move the ring closer to the final position. then attach fins. the middle ring gets glued when you do the internal fillets (or in this case foamed. remember the rings don't carry much load, the fins should be carrying the bulk of the thrust load.
Rex
 
Usually, you want to leave off the aft most CR; till after you glue it into the tube.
What might help here is: notch your CRs with a Dremel tool about an 1/8 of an inch deep.
(It will help grab some of the epoxy)

place your first bead of epoxy just above the fins slots.
Slide the mm into the tube with a twisting motion to spread the epoxy.
Just before sliding the mm all the way in, place some epoxy at the aft end of the tube.
push the mm into postion.


JD
 
Photos are needed as I don't think it's clear of the issue.


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In order to get a good fillet on the middle centering ring, I usually apply a thick bead of epoxy with filler in it to the fore side of the centering ring just before I install it in the tube. The epoxy has to be a little bit runny to allow it to settle and form a fillet after the assembly is pushed in, but not so runny that it gets everywhere when you're installing the assembly. For this purpose, the Glenmarc Rocket Poxy is PERFECT.

I can promise you that this works. I am currently trying to disassemble my Performance Rocketry Competitor 5 that was built this way due to a CATO, and I'll be damned if that motor mount isn't doing its best to stick around.
 
In order to get a good fillet on the middle centering ring, I usually apply a thick bead of epoxy with filler in it to the fore side of the centering ring just before I install it in the tube. The epoxy has to be a little bit runny to allow it to settle and form a fillet after the assembly is pushed in, but not so runny that it gets everywhere when you're installing the assembly. For this purpose, the Glenmarc Rocket Poxy is PERFECT.

I can promise you that this works. I am currently trying to disassemble my Performance Rocketry Competitor 5 that was built this way due to a CATO, and I'll be damned if that motor mount isn't doing its best to stick around.

Yeah that's not an option here in the UK. I've BSI 5, 15, 30 min epoxy that is it!

Here are the photos

3 rd CR not glued yet as foaming the can but will be on the far right once it is



Body tube with it of where it'll be, am using a tail cone hense the MMT sticking out

 
Yeah that's not an option here in the UK. I've BSI 5, 15, 30 min epoxy that is it!

Here are the photos

3 rd CR not glued yet as foaming the can but will be on the far right once it is



Body tube with it of where it'll be, am using a tail cone hense the MMT sticking out


30 minute epoxy should be fine. The Rocket Poxy is a good option, but you can replicate it with what you have.
 
30 minute epoxy should be fine. The Rocket Poxy is a good option, but you can replicate it with what you have.

The point still remains. 1st CR will pass and I can reach down and apply a bead for that but then how do I do the 2nd ring above fin slots.



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The point still remains. 1st CR will pass and I can reach down and apply a bead for that but then how do I do the 2nd ring above fin slots.



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Okay, I'll try again. Do it in these steps:

1. Sand all areas that will have epoxy on them.
2. Apply epoxy to the inside of the main body tube about 1" below the foremost CR's final resting spot.
3. Apply a large amount of epoxy just to the right of where you are holding the motor mount in your last picture. This epoxy, by design, is meant to flow down and out to the OD of the ring and will form a fillet between the CR and the main body tube.
4. Quickly slide the motor mount into place before the epoxy flows too much.
5. Stand rocket on tail and wait for epoxy to flow.
 
I have done this by using 30 min epoxy, but obviously I never got a look inside at the final product to see how well it worked, so these steps are unverified. I guess the only way any of these methods get verified is if the rocket comes to an unfortunate end, so I hope these will remain unverified steps.

- cover off the top 2 in of all but one fin slot with tape.
- place ring of epoxy 1/2 in below where forward CR will be.
- slide MM in until the second CR had nearly closed the window in the untaped fin slot, i.e. just below where it will ultimately be.
- use a syringe to squirt a lot of epoxy into the airframe through the fin slot window. Do this with the tube sitting on either side so you get a good bit on each side of the tube.
- push the MM into it's final place and twist it about a bit.
- Remove tape and clean up any epoxy that got loose.
- Roll airframe slowly on its side to let the epoxy spread around the inside circumference of the tube.
- Stand rocket vertically for 5-10 min. Not long enough to let the epoxy set up.
- Twist MM back and forth to make sure everything is spread out.
- Stand rocket up again to let the epoxy cure.

If you are really curious you can pull the MM down after the first verticle stand, and see if it is all wet with epoxy. I did this the first time, and it definately was completely wetted out and some epoxy oozed from all three slots.
 
I have done this by using 30 min epoxy, but obviously I never got a look inside at the final product to see how well it worked, so these steps are unverified. I guess the only way any of these methods get verified is if the rocket comes to an unfortunate end, so I hope these will remain unverified steps.

- cover off the top 2 in of all but one fin slot with tape.
- place ring of epoxy 1/2 in below where forward CR will be.
- slide MM in until the second CR had nearly closed the window in the untaped fin slot, i.e. just below where it will ultimately be.
- use a syringe to squirt a lot of epoxy into the airframe through the fin slot window. Do this with the tube sitting on either side so you get a good bit on each side of the tube.
- push the MM into it's final place and twist it about a bit.
- Remove tape and clean up any epoxy that got loose.
- Roll airframe slowly on its side to let the epoxy spread around the inside circumference of the tube.
- Stand rocket vertically for 5-10 min. Not long enough to let the epoxy set up.
- Twist MM back and forth to make sure everything is spread out.
- Stand rocket up again to let the epoxy cure.

If you are really curious you can pull the MM down after the first verticle stand, and see if it is all wet with epoxy. I did this the first time, and it definately was completely wetted out and some epoxy oozed from all three slots.

Like this idea a lot. Could I use 15 min epoxy in place of 30?


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Like this idea a lot. Could I use 15 min epoxy in place of 30?


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That depends on how fast you work. Me, probably not. I like to give myself plenty of time. IF you set up your work area perfectly, and nothing went weird along the way 15 min is probaly doable, but not a lot of buffer there.

I don't know how readily available 30 min epoxy is for you, but 5-10 £ is cheap insurance against a mistake that could cost you quite a bit of blue tube (and your trans-Atlantic shipping charges).

Whatever you try, good luck, and I forgot to mention roughing up the inside of the tube with some 80 grit before epoxying. I imagine you know though.
 
Along the same lines, drill a small hole (or 2 or 3) above the flinal spot of that middle ring. Install the MMT with epoxy for the top ring. Unce the MMT is in position, or just below it, use a syringe to inject epoxy through the holes to secure the middle ring. (The injecting could actually be done after the forward ring cures so you don't have to be concerned with shifting the MMT out of place.) After injecting, slowly roll the airframe, while holding it at an angle, to distribute the epoxy around the joint.
 
Along the same lines, drill a small hole (or 2 or 3) above the flinal spot of that middle ring. Install the MMT with epoxy for the top ring. Unce the MMT is in position, or just below it, use a syringe to inject epoxy through the holes to secure the middle ring. (The injecting could actually be done after the forward ring cures so you don't have to be concerned with shifting the MMT out of place.) After injecting, slowly roll the airframe, while holding it at an angle, to distribute the epoxy around the joint.

5 min epoxy to then fill the holes I've drilled?

I could use 5 min to fit the 1st CR then 15 min via your idea?
 
squirt some epoxy into the hole, then put a piece of tape over the hole, rotate the tube until the tape is facing down, let epoxy cure then remove tape.
Rex
 
You may be able to partially insert the MMT into the AF, glob epoxy forward of the fin slots using something like a coathanger, then sliding the MMT into place.

Moving forward, though, consider next time you're using this setup to get CRs to fit the MMT:--

Remove Front CR.
Epoxy AF at center CR ONLY.
Tape ring around back of middle CR to hold in place when pushing forward (but able to pull out the other way).
Slide MMT into position. Slide front CR into place from opposite end --this will keep everything nice and straight.
Stand on aft end, allowing fillet to form around center CR.
Let cure.
Remove front CR.
Remove rear CR.
Slide MMT tube out.
Your center CR will now be in position.
You can now check the center CR's fillet and touch-up as necessary prior to full assembly.


Later!

--Coop
 
Fill the holes just like Rex R said. Becareful about 5min in a syringe. You will need to be very quick to save the syringe. Have more than one available. (Go to the chemist/pharmacy and get a couple from the counter. They usually have them for childrens cough syrup and such, and most times they will give you a couple free of charge.)
5min for the top and 15min for the middle ring will work just fine.
 
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