Mixing glues, what can I use over cardboard hardened with thick CA

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BABAR

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Okay, I am using body tube ring fins with a cut out, hardened with thin CA.

I need to be able to sand the inside and the outside of the tubes after the CA to get a smooth hard surface.

on the version I already did, I put the launch lugs in before I did the CA, which made it just about impossible get the paper in to sand afterwards.

I was thinking I could put tape over the areas prior to CA placement to “mask” it, but I don’t think that will work. Most likely the thin CA will just glue the tape to the tube, and even if it didn’t the thin CA will likely wick under the tape anyway.

so should I CA the area, sand it smooth, and use epoxy to glue the lugs in afterwards?



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neil_w

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I have done something like this many many times, which is: apply thin CA to harden some paper or balsa, while keeping an area clear for a future glue joint (some of this soon to come in my current build). In my experience, when applying thin CA with a Q-tip (not so wet that it is dripping), it mostly stays where you put it. So I just keep the CA away from the part where I will need to glue, and it works fine. You could pencil-mark the keep-out area to make it easier to see what you're doing with the CA.

I squirt a small amount of thin CA onto the Q-tip, and then wipe it around the target area until it stops being effective, then add a little more to the Q-tip, rinse and repeat. It is a very controlled process.

As always, a bit of practice on a piece of scrap tube will show you what's possible.
 
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afadeev

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I need to be able to sand the inside and the outside of the tubes after the CA to get a smooth hard surface.
on the version I already did, I put the launch lugs in before I did the CA, which made it just about impossible get the paper in to sand afterwards.
I was thinking I could put tape over the areas prior to CA placement to “mask” it, but I don’t think that will work. Most likely the thin CA will just glue the tape to the tube, and even if it didn’t the thin CA will likely wick under the tape anyway.
On the low-power rockets, I usually use CA to attach the lugs.
Partly, because launch lugs should not experience much force anyway (if they do, you've got bigger problems). Mainly because they usually get glued to pre-finished airframe that has already had its spirals filled and first few layers of primer applied and sanded smooth. Also, because I find it easier to fill in the launch lug spirals and prime them on their own, off the airframe. Thus, by the time I glue lugs to the airframe, there is little to no exposed paper fiber left to which the wood glue could bind.
CA or Epoxy become weapons of choice, and since I'm usually in a hurry to attach the lugs and move on to final painting, I use CA, with a touch of accelerant/kicker.
On mid-/HP-rockets, I might use epoxy since I would be laying epoxy fin fillets at around the same timeframe in building cycle. On LP-rockets, I hardly ever bother with epoxy fillets, in which case, CA is the glue of choice.

so should I CA the area, sand it smooth, and use epoxy to glue the lugs in afterwards?
You could sand-off the attachment surfaces back down to raw paper, and use wood glue, but if CA had permeated paper tube all the way through, this would not do much good. I find that CA perfectly adequate for the task. Epoxy would be stronger, but would be a bit more hassle.

The only time I had ever regretted using CA for launch lugs was on a mid-power airframe that was getting staged on a flimsily secured launch rod. As I was walking away, the launch-rod angle setting mechanism let go, and the rod with the rocket rotated 90 degrees to come to a rapid stop horizontally, a few inches off the ground. One of the CA-ed lugs ripped off at that point (the other one stayed on). But this scenario exerted stress far in access of the design parameters.

HTH,
a
 
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BABAR

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Very helpful, and makes sense. Once I have permeated/hardened the tubes with CA, I guess it becomes a double glue joint (CA to CA.)

so thin CA for hardening, sanding, and thick CA for lug attachment.
 

lakeroadster

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Kind of academic at this point since the CA is already on, but did you consider using regular wood glue instead of CA?
 

BABAR

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Kind of academic at this point since the CA is already on, but did you consider using regular wood glue instead of CA?
No.

Haven't tried wood glue as a cardboard tube hardener, which is what the CA was for in the first place.

Does it work to use wood glue to harden cardboard tube fins?
 

neil_w

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I believe CA will stick to CA pretty well. It's what John Pursley used to recommend (double-glue joints with CA!). I've used epoxy on CA, with the CA roughed up a bit if possible beforehand.

But I go back to the recommendation of my previous post which is simply to keep the CA away from the glue joint area, and then use wood glue normally. This is easy and works great.
 

BABAR

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But I go back to the recommendation of my previous post which is simply to keep the CA away from the glue joint area, and then use wood glue normally. This is easy and works great.
for medium and thick CA you are as usual spot on.

for hardening of the paper tubes, I am using thin CA which basically wicks into the cardboard core, rather than simply coats the surface like most glues. Which since I am trying to harden the whole tube fin, makes sense. But I think because this spreads by “wicking” through the porous paper, I don’t think masking would work, I think it would just “wick around” (over, under, if not through) the mask.

although there is one possible work around. I could lay down the wood or white glue for a double glue joint FIRST.


let completely dry

Then wick in the CA.

let completely dry

Then sand the surfaces to smooth the CA fuzzies. The sanding won’t do much to the wood or white glue base (will likely sand the CA off of it, though.)

THEN use wood or white glue to attach the lug to the previous glue point.

thoughts?
 

neil_w

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I have done something like this many many times, which is: apply thin CA to harden some paper or balsa, while keeping an area clear for a future glue joint (some of this soon to come in my current build). In my experience, when applying thin CA with a Q-tip (not so wet that it is dripping), it mostly stays where you put it. So I just keep the CA away from the part where I will need to glue, and it works fine. You could pencil-mark the keep-out area to make it easier to see what you're doing with the CA.

I squirt a small amount of thin CA onto the Q-tip, and then wipe it around the target area until it stops being effective, then add a little more to the Q-tip, rinse and repeat. It is a very controlled process.

As always, a bit of practice on a piece of scrap tube will show you what's possible.

although there is one possible work around. I could lay down the wood or white glue for a double glue joint FIRST.
This seems like it would work, although again I don't see that it is necessary.
 

BABAR

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This seems like it would work, although again I don't see that it is necessary.
Where I failed the first time was using thick (or medium) CA to glue luglets (two short lug segments) to a tube which had been hardened and sealed with thin CA. the lugs broke off.

question 1. Why not glue lugs on BEFORE hardening the tube with thin CA?
Reason: I like to sand the hardened surface to get the fuzzies off, and it’s hard to sand the inside of the tube if the lug is already there (remember it is a partially cut tube so the inner surface is both visible and exposed to airstream and gets painted)

question 2. Why not put the lug somewhere else?
Reason: the rocket spins after apogee around central axis. “hiding” the lug inside the tube results in least aerodynamic resistance to longitudinal spin (although may be significant, these are somewhat uncharted waters.....er.....skies.)

I think next time I will use thin CA to harden the surface, sand it smooth, then rough up the attachment are for two full length tube lugs, on opposite sides (trying to keep it rotationally balanced.). The use epoxy to glue the lugs in the rough areas skip the fillets. If one breaks off, I can still use the other one until I fix the first one.
 

neil_w

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Question #3: why not try what I suggested? Experiment on a piece of scrap tubing.
 

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