Av-bay on cardboard rocket tight, does not slide smoothly into airframe, help please

Last year I had a fiberglass av-bay that was too tight going into the airframe, and the folks on this forum gave me some tips that solved the issue, see https://www.rocketryforum.com/showt...s-to-fit-coupler-to-airframes&highlight=tight

Now I'm having a similar problem with a cardboard rocket, but the previous tips do not appear to be working, perhaps different methods are needed for cardboard. Both sides of the av-bay slide smoothly into the upper airframe, but both sides are too tight going into the lower airframe. I've hand sanded with a variety of coarse and fine sandpapers but the problem persists. I've tried drawing concentric circles with a dry erase marker to show the high areas. This tip worked great on the fiberglass but seems not to work with cardboard, as the ink just sinks in and does not leave marks on the high spots. With the fiberglass, it was suggested to clean out the tube with alcohol after sanding to remove particles, but that does not seem effective on cardboard. Talcum powder also did not help.

Any tips for getting a good smooth fit on a cardboard rocket?
Thanks, Bill

what I did with mine, was to apply thin ca to the coupler and allow to harden, then sand with 320 grit, finish with 400 grit. makes for a nice smooth fit.
Rex

Probably swollen from all the rain & humidity. Try coating it with epoxy watered down with denatured alcohol.

What I do is flood the inside of the body tube and half the coupler with thin CA. I mount the coupler on my lathe and sand smooth. Usually, hand sanding the inside of the body tube is enough, but if necessary, I use the sandpaper-on-a-stick tool.

These guys are giving great advice. I've done the same thing as them. I've used thin CA for couplers and body tubes on LPR rockets, and I've used laminating epoxy for couplers on 4" LOC tubing. They both work, but the laminating epoxy isn't as noxious to work with.

For your raised parts, I would think a heavy application of pencil graphite would do, though much messier.

*deleted*

But I see I wasn't quick enough.

MikeyDSlagle said:

Click to expand...

yea yea we know!

Thanks for the replies. As glue is usually used to stick things together, I would never have thought of applying CA or epoxy to make the connection looser.

billdz said:

Thanks for the replies. As glue is usually used to stick things together, I would never have thought of applying CA or epoxy to make the connection looser.

Click to expand...

CA when cured makes a plastic like surface and its very hard, once sanded its nice and smooth. Many if us soak the ends of our cardboard tubes with it to toughen them up. Epoxy thinned with a little denatured alchol can do the same thing, but seems to be less consistent and takes much longer to cure.

rharshberger said:

CA when cured makes a plastic like surface and its very hard, once sanded its nice and smooth. Many if us soak the ends of our cardboard tubes with it to toughen them up. Epoxy thinned with a little denatured alchol can do the same thing, but seems to be less consistent and takes much longer to cure.

Click to expand...

Do you apply the CE or epoxy with a brush, or dip the coupler into the glue, or what?

Diluted epoxy can be applied with acid brush or chip brush.

For CA, I use the teflon tube spouts ( teflon tubing inserted into tip of thin CA bottle) flood it on while manipulating the part so the CA flows where its needed.

qquake2k said:

I just use the tip on the CA bottle, and literally "flood" the surface. Then wipe it with paper towel. Be sure to wear latex or nitrile gloves!

Click to expand...

And do it outdoors! The fumes are horrible.

BDB said:

And do it outdoors! The fumes are horrible.

Click to expand...

I have found that chemical splash goggles help a little with keeping the fumes out of your eyes.