Tube Coupler Hack

[neil_w]

I'm struggling to find it by searching, and I'm not motor guru, but I believe it's as simple as this: The C5 has a larger and/or deeper core drilled into it, so when it is initially started there is a lot more surface area of burning propellant. This creates much higher thrust during that initial burn, and also consumes more propellant.

 

[brockrwood]

Oops. Note to self: If the tube fits over the coupler tightly when dry, it will “seize up” and not go all the way on when glue is applied to the joint.



Now I need to find a leftover decal from another kit that is big enough to cover the gap…

Or not. I mean, it is a Frankenrocket, after all…

 

[lakeroadster]

Oops. Note to self: If the tube fits over the coupler tightly when dry, it will “seize up” and not go all the way on when glue is applied to the joint.

View attachment 520872

Now I need to find a leftover decal from another kit that is big enough to cover the gap…

Or not. I mean, it is a Frankenrocket, after all…

View attachment 520873

What kind of glue did you use? White glue works best... it's less "grabby".

And don't dilly-dally. Put the glue on and drive the coupler home. There's a time for slow and methodical... and this ain't that time.

 

[BABAR]

What kind of glue did you use? White glue works best... it's less "grabby".

And don't dilly-dally. Put the glue on and drive the coupler home. There's a time for slow and methodical... and this ain't that time.

Yup, paper to paper and white glue is your friend when you are not in a hurry, and for most coupler and engine blocks you aren’t. For paper to paper or cardboard the bond is effectively as good as wood glue or epoxy, probably better than CA.

For coupler and engine blocks, before glue, test fit once, test fit twice, mark to the casing/pusher for the motor block depth. once you know exactly where it is gonna go, put the glue in place, shove it in with the pusher or used motor casing for the motor block quickly and smoothly and immediately pull out the pusher.

that gap might be fillable with masking tape. Get a roll, measure the gap, and cut a slot around the roll to get a strip the width of the gap. Wrap the tape around until you are flush with the adjacent surfaces. if you are into two foot finishes you can use CWF or Bondo to fill the minimal remained gap, me, I’d put a wrap of colored Mylar tape around it (or a decal) and call it good.

 

[brockrwood]

What kind of glue did you use? White glue works best... it's less "grabby".

And don't dilly-dally. Put the glue on and drive the coupler home. There's a time for slow and methodical... and this ain't that time.

I used Titebond III. Usually it doesn’t grab on me like this, but the fit was pretty tight. From now on, only Elmer’s on tube couplers.

 

[brockrwood]

I left the pink launch lug from the Big Rage on the upper tube. It is epoxied on. I figured maybe I could use it to attach a glider or other accessories. Like a trailer hitch.

 

[neil_w]

I used Titebond III. Usually it doesn’t grab on me like this, but the fit was pretty tight. From now on, only Elmer’s on tube couplers.

For absolute maximum slidability there is also epoxy.

 

[brockrwood]

For absolute maximum slidability there is also epoxy.

Epoxy slides easily when used on a tube coupler? I will try that next time! And, of course, you get the crazy strong bond of epoxy.

 

[neil_w]

Epoxy slides easily when used on a tube coupler? I will try that next time! And, of course, you get the crazy strong bond of epoxy.

Epoxy is very lube-y before it starts firming up. Strength-wise, I wouldn't expect it it to be any better than white or wood glue for a paper-to-paper bond.

As is always the case with epoxy, you need to make sure you have everything held in position while it cures.

 

[brockrwood]

Applying wood glue to a tube coupler seems to just slightly swell the paper when applied. Then the tube fit that was “perfect” (not too snug, not too loose), is too snug. So if I use wood glue for couplers, I guess I need to make the initial test fit, dry, before applying glue, a little bit loose. That way the fit will be “perfect” after I apply the glue.

But then, if the fit is too loose, I fear the two tubes will mate together “crooked” and not be in perfect alignment.

Like most techniques in model rocketry, it is as much art as science. Practice makes perfect.

 

[BABAR]

Applying wood glue to a tube coupler seems to just slightly swell the paper when applied. Then the tube fit that was “perfect” (not too snug, not too loose), is too snug. So if I use wood glue for couplers, I guess I need to make the initial test fit, dry, before applying glue, a little bit loose. That way the fit will be “perfect” after I apply the glue.

But then, if the fit is too loose, I fear the two tubes will mate together “crooked” and not be in perfect alignment.

Like most techniques in model rocketry, it is as much art as science. Practice makes perfect.

Put the glue on the inside of the tube, not the coupler. Keeps all the “run off” in the tube. And if you work reasonably quickly (hence the test fits) things don’t have time to swell up.

In my experience if it test fits smoothly but firmly you should be fine with white glue or epoxy.

 

[brockrwood]

Put the glue on the inside of the tube, not the coupler. Keeps all the “run off” in the tube. And if you work reasonably quickly (hence the test fits) things don’t have time to swell up.

In my experience if it test fits smoothly but firmly you should be fine with white glue or epoxy.

I put on the coupler and on the inside of the tube. Doh! As usual, I kind of overdid it with the glue. I am a glue maladroit.

 

[BABAR]

I put on the coupler and on the inside of the tube. Doh! As usual, I kind of overdid it with the glue. I am a glue maladroit.

Not at all. Sounds like you were trying to do a double glue joint. For many Rocket construction purposes, particularly surface mounted fins, this is a time honored and effective method of getting a relatively quick adhesion. Put a small amount of glue on both surfaces (or on one and then tough them together and pull them apart), give them a minute or two, then attach them (of course, REALLY smart people like @kuririn tack the fin on at the ends with CA and fill in with wood glue).

epoxy is also great for lots of things, I just don’t like the smell and I don’t like to have to wear gloves, and since most of my stuff is low power there are adequate alternatives.

 

[BABAR]

 

[BABAR]

 

[brockrwood]

Keeps all the “run off” in the tube

Great idea! Will do from now on.

 

[brockrwood]

Frankenrocket first launch was a success! All three engines in the cluster lit at the same time. The bird got off the pad FAST!