I printed the SP13 project again and followed all of Steve's advice to the letter:
- bearings cleaned with solvent
- axles cut to size and finished with the Dremel
- very small spray of WD40 on the bearings and the ends of the axles
The clock works perfectly with a weight of just 2.5 kg!
The amplitude of the pendulum in steady state is about 6 degrees so largely reliable.
further update.
I brought the weight down to just 2 kg and the watch continues to be very reliable with an oscillation of almost 6 degrees!
Very attractive choice of colors!