Coupler Tube Binding

[d.bloomquist]

I'm working on a 4" Fusion dual-deploy HP rocket. The lower coupler binds with the body section above it. It will come apart if I use a turning action (i.e. "unscrew" the two pieces), but not so easily if I pull straight out. I'm afraid that the black powder charge will blow apart the rocket instead of separating the two sections. I've tried sanding down the coupler and body tube with 220-grit sandpaper, but that just seems to rough up the cardboard. Am I overly concerned about this? Is there something I can do so that the two sections release more easily?

 

[Banzai88]

Not unheard of to have some binding based on variability of parts and humidity. Sanding the coupler is how I've always approached it. I also use sanding sealer on my couplers to make a 'poor man's phenolic' out of it, as it seems to sand better and make for a smoother final fit. I use 220 to get the rough fit, 320 for the final fit, then sanding sealer, then a 600 grit sand.....smooth as silk!

 

[ThirstyBarbarian]

Yep, sanding is the way to go.

I’ve never used sanding sealer, but that would probably help. What I have used is super-thin CA applied to the cardboard with a foam brush and then sanded. I’m sure it accomplishes about the same thing as sanding sealer. It prevents the fuzzies from the sanded cardboard and makes the sanded surface nice and smooth.

You are on the right track. Just keep sanding…

 

[sriegel]

I second the CA soak and sanding. You can also try adding a shot or two of graphite powder (near the key cutting kiosk in Home Depot, e.g.)

 

[Hobie1dog]

finer sandpaper to get it slick is the solution

 

[pathtouch]

For my big 7.5” LOC tubing, I cover the coupling in graphite to help it slip apart. Worth trying after you do some sanding.

 

[David Schwantz]

Do not sand the coupler around it, use linear motions.

 

[Lord Rory Gin]

I'm working on a 4" Fusion dual-deploy HP rocket. The lower coupler binds with the body section above it. It will come apart if I use a turning action (i.e. "unscrew" the two pieces), but not so easily if I pull straight out. I'm afraid that the black powder charge will blow apart the rocket instead of separating the two sections. I've tried sanding down the coupler and body tube with 220-grit sandpaper, but that just seems to rough up the cardboard. Am I overly concerned about this? Is there something I can do so that the two sections release more easily?

I also dislike too tight of a coupler tube. I discovered a solution the other day. I've tried peeling and sanding, neither to any great success. So I tried wet sanding and that was marginally better.
Then I tried wet peeling. SUCCESS!

I wetted the outer layer, then wiped off the excess water. I wanted just enough water to wet the outer layer but not soak it through. Then I picked one of the triangle corners and started to peel. Surprisingly easy and I used a constant easy pull. And I just kept peeling and turning and peeling in the direction of the winding. It came off in ONE PIECE. I didn't even have to sand it later although I could have to knock off the fuzz if I needed to. It was the perfect fit for the tube (4" LOC Phoenix). Edit: I sanded it later with extra fine to get rid of the fuzz.

The only unfortunate thing was that I forgot to video it because I was so surprised it worked that well.

 

[d.bloomquist]

Thanks to all of you who offered suggestions on resolving my binding coupler. I ended up applying sanding sealer and then progressively sanded it with finer and finer sandpaper. Worked like a charm!