Now that you have your printer up and running, you could work on a scale Delta II.
Been there, done that.
My booster mounts were built similar to the ones Apogee have, but I made them by hand from various thicknesses of plywood and a brass rod.
I posted these images back in 2004 here under the screen name of qMaxx, but they're not in the posts anymore. I forgot that I had that name here when I re-registered here recently. Anyway, the two launch images are of the two versions I built. The first test model (on the left) had a successful ignition of all ten motors (core D-12 and A10's in the boosters), but the delay on the D was too long - my fault. The boosters all separated fine.
The second model (the right image) only had five of the A10's light, all on one side, so the model crabbed its way to about 50 feet, still pointing straight up, before landing butt first and shoving the main motor mount up into the model. It was nice to see that even though the thrust was off-center, because of the ten-degree cant of the motors, it still went up, instead of flipping end-over-end.
After the second failed - in the Elon Musk/Starship sense of the word "failed" - flight, I got extremely discouraged and basically quit rocketry. So, for 20 years, I've basically done nothing. Now I'm getting back into it and am already working on prototyping printed parts for a new Delta II model*, which I hope to test fly sometime next year.
*Much easier/cheaper to built test models now. Back then, I was making everything from scratch, and having to compromise on scale accuracy due to limited tools available and lack of funds to get the tools. I've had a 3D printer now for 3 years, will be getting a laser cutter in a couple months, and spent the intervening 20 years off-and-on teaching myself Blender 3D modeling (not about to do the same with CAD software - I'm 59 and don't have that kind of time anymore).
