I tuned up the plastic retainer to make it as small as possible while maintaining functionality, and will fly it as is on the teeny triskellion, but when I was sleeping I devised a way to make proper threads in all MMX size motor tubes.
As expected, JB Weld will be used, but that idea about the revers Heli-Coil will not be necessary.
I will start with a fresh build, and a fresh un-primed tube. I will sand the outside of the tube down very carefully, using my caliper to ensure that I only remove the outer most 25% of the thickness. I'll then drill 4-5 tiny holes about 1 millimeter from the aft, that will form "Epoxy Rivets" of the JB.
Before application of the JB, I'll carefully harden the area with thin CA, to lock the fibers of paper into place to prevent the torsional forces of use from degrading the tube over time. I will allow this to fully cure and off-gas before proceeding to the JB Weld.
I will wrap some Teflon tape around a spent motor casing, and place it in the tube prior to applying the JB, so the internal surfaces are not to tricky to clean up after the epoxy has cured.
I'll mask off the portion of the MMT that I don't need threaded, as we won't want any mess that would add to the weigh unnecessarily.
After I get a layer of JB worked in, I will take one of those annoying "Whisps" of Fiber Glass cloth, likely jut from say 1oz. stuff, and cut it to the proper length and wrap it around the portion to be threaded, and press it gently into the JB. I've pressed individual FG fibers into JB Weld before for a couple tiny things and it has worked fine, but if I determine this to be a pain, I'll chop the single fiber into dust and press this into the JB instead.
When the JB is cured, and PRIOR to removing the masked motor, I will sand to proper spec. using my caliper to guide me, then use a thread cutting die of the appropriate aspect to render threads to the prepared portion of the tube.
Once the threads are cut, a drip of regular CA, and then a second run though the die should yield a nice finish.
This in my mind should be the most efficient and serviceable method for creating a repeatable and long lasting thread to screw the tiny retainers onto.
I first considered using Aluminum HVAC tape, but it is too thick, and I expect the glue would degrade over time, especially given the corrosive nature of the black powder residue.
I have drilled and tapped JB Weld in the past, but have never used it to render threads externally, yet at this tiny scale, and using the malleable plastic caps, I believe it will be efficient.
I'm designing a new model with enough length to give me a good stability margin to be able try different brands and styles of caps as a test platform.
A Micro-Grey Scale Zero.
The BBZ design has stability coming out it's ears!
