The GT2 / GT3 belt specs call for 10-ish pounds of tension, but I don’t yet have a good feel for the actual MPCNC belt tension … and it’s hard to measure in-situ. So I picked up some spring tensioners and yanked one with a luggage scale:
You’re looking at 4 kg = 8-ish pounds of tension. When they’re relaxed, the arms sit at roughly right angles.
I installed them on the far end of the belts, although that’s a bit snug under the roller:
An endstop switch will eventually add some clearance and it’ll be all good.
Even though they’re neither linear nor precisely calibrated, they’ll serve as a reminder to check the tension every now and again.
Install them with the same casual disregard you reserve for fish hooks and you’ll emerge unscathed.