As most people are coming to realize, the MT3 keycap profile for mechanical keyboard keycaps is the best :-)

The profile designer, Matt3o has released high quality STL files for 1u R0, and 6.25u spacebar at https://matt3o.com/mt3-stl-files-for-artisan-keycap-designers/

 

I needed a couple of short spacebars for some split keyboards, so used pymesh to slice and dice the 6.25 into alternative lengths. 

 

The python script is included, and it should be easy to run the script using docker to generate additional length space bars.  Something like this should work to produce a 2.75u spacebar with a key stem and stabilizers spaced like a 2.25u space bar:

docker run -it --rm -v $(pwd):/models pymesh/pymesh python /models/spacebars.py -u 2.75 --stem --stab-2.25 /models/MT3-spacebar-6.25u.stl /models/my_spacebar.stl

Options for stem placement:

• --stem: make a stem for the switch, at position 0 (center of the keycap)
• --stem-u: make one or more stems at offsets designated in u units
• --stem-mm: make one or more stems at offsets designated in mm
• --stab-2.25: shortcut for stabilizer stems for a 2.25u keycap, (i.e.: equivalent to --stems-u -0.625 0.625)
• --stab-6.25: shortcut for stabilizer stems for a 6.25u keycap (i.e.: equivalent to --stems-u -2.625 2.625)

I printed these on my new Elegoo Mars 2, and have yet to experiment with appropriate resins to use.