Jim G's work inspired me to work on a 40/20 meter trap doublet/dipole/inverted vee with 3D printed trap coil forms and insulators. I have the traps coil forms done and the end/trap center insulators done and I really got lucky. A 20 meter trap should have 4.7 uH worth of inductance with a 27pF capacitor to resonate at 14.100 MHz and TOTALLY by accident, my initial print of the coil form wound with 16 turns of #20 wire just so happened to come out to just a bit over 4.7uH when I measured it.
I worked on the design (I used AudoDesk's (free for personal/non-commercial use) Fusion 360 as my CAD program. F360 gives a bit more finesse when making threaded cylinders than TinkerCad does.
Taking Jim's advice, I also added blockers to the inside of the coil form so the insulator will slide tightly inside and allow you to wind the coil first and pick which 90 degree point gives you the best coil positioning.
Here's a couple of pictures of the lot.
Jim Sheldon, W0EB -- 3D printing is a super 2nd hobby to HamRadio --