A 3 axis gimbal I designed for a test fixture at work. The original had printed corners and machined sides due to our printer not being large enough to print all the sides. I did a test print of the bearing hole in ABS with a 0.4mm nozzle and standard Fine settings in Cura 2.6 on our Ultimaker 2 and the bearing was a nice press fit.
Stainless steel pins are used for the locking mechanisms. They were machined with grooves for 4 C-clips but I have listed external push rings which will work although you will only be able to install 3. Be sure to round off at least the one end of the pin so it will slide easily into the locking hole. Stick a block under the outer locking ring plate of sufficient height for the locking pins to clear the next ring by about an 1/8" and slide the inner locking ring up against the wall and seat in place with the external push rings. We reamed the locking pin holes to 0.128" and got a nice sliding fit which would stay back out of the way when in free swinging mode.
We used slip rings from Adafruit (https://www.adafruit.com/product/1195) to get power and data into the center.
Assemble from the inside to outside (inside, middle, outer, outer #2). I used a washer on both sides of the joints for extra support. Use extra walls on the base so you can tap the 1/4-20 holes.
UPDATE 8/23/17: I have added a 15 pin D-Sub mount that I am using to route the wiring to the inner ring.
Qty 12 6002-2RS Bearings (https://www.mrosupply.com/bearings/radial-ball-bearings/198079_6002-2rs_mro-supplier/?utm_source=google&utm_medium=cpc&utm_campaign=PLA&gclid=CjwKEAjwytLKBRCX547gve7EsE4SJAD3IZV6zCv62K_1SBd9hn_NGk5gfS121ynEwXCE-ol0pIBwzxoCu93w_wcB)
Qty 1 pack Black-Oxide 18-8 Stainless Steel Hex Drive Flat Head Screws 1/4"-20 Thread Size, 7/8" Long (https://www.mcmaster.com/#93791a417/=18p1jt1)
Qty 2 packs 18-8 Stainless Steel Dowel Pin
1/8" Diameter, 2-1/2" Long (https://www.mcmaster.com/#90145a487/=18aplla)
Qty 1 pack External Push Ring
18-8 Stainless Steel, for 1/8" OD, 7/32" OD (https://www.mcmaster.com/#97200a020/=18p1m37)
Qty 1 pack 18-8 Stainless Steel Nylon-Insert Locknut
Black-Oxide, 6-32 Thread Size (https://www.mcmaster.com/#94407a101/=18hgn9e)
Qty 1 packs 18-8 Stainless Steel Hex Drive Rounded Head Screws
Black-Oxide, 6-32 Thread Size, 3/4" Long (https://www.mcmaster.com/#97763a328/=18p1mp8)
Qty 2 packs Black-Oxide 18-8 Stainless Steel Washer
for Number 6 Screw Size, 0.141" ID, 0.375" OD (https://www.mcmaster.com/#96765a115/=18hgnmg)
OPTIONAL BRASS HARDWARE FOR REDUCED MAGNETIC INTERFERENCE (and a really cool look!):
Qty 1 pack Brass Phillips Rounded Head Screws
6-32 Thread Size, 3/4" Long (https://www.mcmaster.com/#94070a151/=18ozels)
Qty 2 packs Brass Washer
for Number 6 Screw Size, 0.147" ID, 0.312" OD (https://www.mcmaster.com/#92916a325/=18ozf0z)
Qty 4 packs Brass Nylon-Insert Locknut
6-32 Thread Size (https://www.mcmaster.com/#92092a021/=18ozfcz)
Qty 1 pack Brass Phillips Flat Head Screws
1/4"-20 Thread Size, 1" Long (https://www.mcmaster.com/#92480a545/=18ozi9c)