Two! Finally made it official this year, after twenty years with one (my first girlfriend), and the other having been with us for thirteen.
I too have gotten some good stuff from there.
Do you think you could just print the mold directly? I haven’t looked deeply into the techniques.
The pillory was pretty simple, so I didn’t feel the need for a plan. I had the pillory part sandwiched between a pair of 2X4s with regularly-spaced holes on each end. Long bolts ran through the sandwich, and could be removed to adjust the height. Most of the time it was attached to the bed, but I also made a base out of a pallet so it could be used freestanding. Sadly I don’t have the bed anymore. I need to find a place for the pillory in my new house and pull it out of the garage. 
I have not used that kind of sleeve before, but earlier this year my wife got me one that fits on the head of a Hitachi-style wand vibrator, like this one. I have enjoyed it. I don’t know that it is better than a hand, but much like my electric toothbrush, it is nice letting a motor handle the rapid back-and-forth.
I have made a pillory, a St. Andrew’s cross, a spreader bar and a couple collars. I processed and dyed a big spool of hemp rope into nice shibari ropes. Installing a bunch of tie-down points around and above the bed and fitting them with chains probably counts too.
When I was experimenting with a laser cut, I made what I think is my most original design, this tag that goes over the bar of a nipple piercing, and is held in place when you screw the balls on the ends. 
Though this cat toy that I made into a gag for my bunny girl turned out pretty cute, too. 
I don’t have any pictures yet, but I am just finishing up a pony play head harness modeled after this one, and am quite happy with how it is looking: https://www.lvxsupply.com/collections/featured/products/bit-gag-bridle
Insertables sound interesting, and could synergize with my 3D printing hobby, but the only silicone I have ever cast was a single mold for resin.
Nice work. That’s an interesting combination of subjects. Though now that I think about it, the riddle of the Doors of Durin would make a pretty fantastic lower back tattoo.
I (male) don’t like anal sex, though I will grudgingly give it. My wife wants it in the butt. I feel like the preference mismatch for this act usually runs in opposite direction.
CNC. I do plenty of BDSM, but as the male aggressor, I still find CNC an embarassing kink to have. I am not sure if my partners would be into explicit resistance play; I am sure they would indulge me, but I don’t think I would want to set up such a scene unless it was with a sub who was unequivocally into it too.
Also, the thought of impregnating a woman is very erotic. As someone with zero desire to be a parent, I am staying well away from that.
I picked up a cheap goat milking machine a year ago. One of my wives loves the sensation it and uses it frequently.
https://www.amazon.com/gp/aw/d/B09P3746R6
You can also get some hooves and a cute cow-ears handband so that your livestock is appropriately attired.
I would greatly enjoy more foot massages. Not for any sexual reasons, but just for the relaxation of it. I really should start giving more if I want to receive…