$1.50 29mm retainer

Just finnished "Thumper", a BT-80, 29mm fired scratch built.

for the motor retainer I used from home depot:

1) 1-1/4" PVC male adapter
2) a 1-1/4" slip nut
3) a fender washer

I cut about 1/2" of the threaded part off the PVC male adaptor,
I extended the 29mm motor tube out of the rear centering ring so it was about an 1/8" recessed in the PVC threaded section, when I laid the threaded PVC on the centering ring. Next I epoxied the motor mount in (with the fins in My case), Then I epoxied the PVC male threads onto the rear centering ring/motor tube.
The 29mm tube fits into a 1-1/4" PVC just right, need about 1 wrap of masking tape to make it snug. I drilled 1/16" holes in the rear centering ring and the PVC to aid the epoxy.

A 29mm RMS hobbyline case will "just" slip through the 1-1/4" slip nut, so I used a fender washer (from the hardware isle), The O.D. fit perfect into the slip nut, and I used a die grinder to open the center up to clear the nozzle (and reduce weight).

You can use the "grey" PVC conduit in the elec isle, it feels slightly lighter.

4 flights, perfect with no damage.

Slack

A rear shot, now that I look, the 29mm tube is recesseda little more than 1/8", You will have to mook up with Your casing.

Here it is (after a few flights), I used the grey 1-1/4 nut from in the electrical isle.

Slack

How well will something like that work for 38mm?

1-1/2" slip nut and male PVC threads may work, just have to take a piece of motor tube to home depot and wonder down the isles.

Slack