Canted switch band fix

[Mr G]

After the glue had dried, the 1" switch band on a 4" cardboard Super DX3 was found to be canted relative to the body tubes so there is up to a 3/16" gap on opposing sides when all the pieces are slid together. Does anyone have a good method to fill the gaps so that glue/filler doesn't stick to the wrong pieces and the fix is strong enough that it won't chip or break off? The objective is to have a smooth transition so that, when fixed, the switch band will have essentially increased to 1 3/16" all the way around and when sanded and painted no one would know the difference.

 

[dixontj93060]

I prefer to file down gaps and undulations if they aren't too big, but in your case with a large 3/16" gap, yes, I would likely try to fill it. Personally I would use Saran wrap and cover the gap areas on both the booster and payload section by taping internal and external to airframes. Then fit the frame together and layer on a strong filler. By strong I mean an epoxy based product like SuperFil or System Three SilverTip QuikFair. I suppose you could use epoxy thickened with microballons, but I would feel more comfortable with a pre-mix as I know exactly how hard it will set up and how thick the consistency is for the initial fill (so it won't gap or run). After hardening remove the Saran wrap, fit back together and carefully sand with 120 grit or so (since it is a cardboard airframe you will want to make sure you don't dig into the glassine). As you get close to the base airframe switch over to a 220 grit or less to do the final feather sanding.

 

[Spicer007]

Mr G,

I had the same problem with my DX3 build. Trimming it to fit squarely will be extremely difficult and will narrow the band significantly.

I bought a replacement switch band from Madcow Rocketry, cut the cocked switch band off and cleaned the cured glue off the av-bay. Then dry fit the new switch band on the av-bay, marked the position by running a band of painters tape around the av-bay and a pencil mark on the other opposite side of the band, to indicate were to place the adhesive.

I also used epoxy to allow time to position the switch band. If you use carpenters glue or Titebond, the glue will catch too quickly and it's difficult to position the band properly. Spread the epoxy between the pencil mark and the tape. Slide the new band onto the av-bay to the tape band. Clean off the excess epoxy from the band with alcohol and check the alignment by sliding it on the BT. When your satisfied with the fit remove the tape and let the epoxy cure.

Or if you have a scrap of 4" BT you can cut a 1" band and avoid buying a new switch band.

Good luck...

 

[Handeman]

I would recommend Mr. G's solution. Not only does the band affect aerodynamics, but if it isn't square and true to the BTs, it will induce bending forces when thrust is applied and the G forces push the BTs down onto the ring. Getting the band on right is more important as the G forces go up.