How I finally got motor retention right on my printed rockets

I stopped fighting printed motor tubes altogether on my last couple of builds. I print the airframe but glue in a standard cardboard motor mount tube with a centering ring up top, and it's been trouble free ever since. The layer lines inside a printed bore just chew up the casing and make the fit inconsistent depending on which motor brand you grab. A cardboard tube takes glue beautifully and gives you that consistent wall you want. For retention I've had good luck with a simple screw-on retainer I printed in PETG. I put one on my Aerotech 24mm mount and it's held through a dozen flights now. Before that I was doing the tape wrap thing and honestly it worked okay, but I lost one motor on a grass landing when the tape let go on impact and the casing slid out into the weeds. Never found it.

One thing I'd add about the thrust ring: make sure you position it for the longest motor you plan to fly, then use spacers or cut the forward end to fit shorter casings. I got this wrong on my first printed rocket and my E motors sat too deep, which put the ejection charge right where the ring blocked half the pressure. That flight had the laziest chute deployment I've ever seen, and the rocket came in hot on a streamer I didn't even pack.

Another vote for the tape wrap, but with a twist that saved me some grief: I was getting inconsistent ejection becasue the tape would weld itself to the casing in summer heat. Switched to the cheap blue painter's tape instead of masking and the problem went away. Shears clean every time now, even after sitting in a hot car at the field all morning. For the thrust ring, mine kept coming loose in the printed tube untill I scuffed the inside wall with some coarse sandpaper and used two-part epoxy instead of CA. That ring has not budged in two seasons.