This is a centered vise from a school project that I have designed to be 3d printable. It's a fully working model with its included mechanical parts. It's not the usual vise since we offer a quick release jaw system, have that in mind when printing. :) 
(If you are using this for actual use, I recommend printing in PETG especially for prolonged tension.)

Printing:
Some of my print profiles has ironing. Make sure to calibrate your ironing before printing. 

Hardware:
2x springs from MX switches any weight (suggested over 50g, mine has 150g :) …)  (Pen springs might work I haven't tried)
2x M3x30mm countersunk screw 
10x M3x10mm countersunk screw

Assembly: (desclaimer: Names of parts are in danish)
Step 1. “Base” → “Holder Til Spindel bund” → “Body1_a” and “Body_1B” → “Holder til Spindel Top”.

Step 2. Screw in top bracket with the two M3x30mm screws.
2x Step 3. "Slæde" → put the spring in the hole on top → put the "Stift" over the spring → put the "Låg til Slæde" on the pin

2x Step 4. Screw down the "Låg til Slæde" on the slider with 2x M3x10mm screws.

Step 5. “Base” → “slæde” on each side → Fit both threaded inserts ("slædegevind") on the rods so they line up around the same point at the end.
Step 6. Slide the sliders ("Slæde") onto the inserts and tighten the with a m3x10mm screw
2x Step 7. “Kæbe” → “knap” → “Låg til kæbe”
2x Step 8. Screw down the “låg til kæbe” with 2x m3x10mm screws
Step 9. Slide “kæbe” on top. 
Step 10. Send me a picture and then DONE!