Richard Johnston's original design and Simon Gay's adaptations were followed with two exceptions ...
1) My local hardware supermarket didn't stock rubber tap washers. The washers available appeared to be made of a black plastic, possibly nylon from the ease with which they accepted a drill bit. When fitted, these black plastic washers did the job, but made an annoying clunking sound, which was particularly noticeable at handstroke, when the bells are close to the ears, especially when the O-rings were fitted to the clappers, and the bell sound volume consequently reduced. I tried cutting the moving washer into a diamond shape to reduce its stiffness. This had the added advantage of being able to control the distance between clapper and bell by rotating the diamond on the clapper shaft. However the clunking noise remained. My current design dispensed with the stationary washer. Two 4.5 mm diameter holes were drilled in the remaining washer, and 8 mm lengths of round, 5 mm diameter, catapult elasic tubing, obtained from the internet, were twisted into these holes, with the upper ends flush with the surface of the washer closest to the clapper. The assembly was completed with the addition of a brass washer to help secure the elastic tubing, and a 14 mm length of clear plastic tubing between the brass washer and the clapper ball. With this arrangement, the bells were useable both with and without the O-ring on the clapper, producing a large change in volume, and the annoying clunk was gone.
2) I wanted to avoid the use of glue, so that the clapper unit was easily replaceable. The circumferential grooves round the clapper balls to accept the O-rings were cut with a round file used for sharpening chain saws. The clapper ball was fixed to the hinge shaft by drilling separately through the clapper ball with a 2.5 mm drill, and then along the length of the shaft of the hinge with a 2 mm diameter drill. The clapper ball was then secured by means of an 18 mm 4G brass screw trough the clapper ball and into the hinge pin. The hinges proved to be hollow, so an alternative would have been simply to cut the end off the hinge pin. In the finished assembly, the countersunk screw head resembled a brass flight on the clapper ball which was quite pleasing. The leather for the handles was purchased from the local cobbler, and attached to the handle of each bell by four 12 mm 4G plated steel screws. The screws were positioned two on either side of the handle, 10 mm and 25 mm back from the circular leather caps, which were themselves separated from the bell by rubber O-rings as suggested by Simon Gay. The two screws closest to the bell almost made contact inside the plasic handles. These two screws were loosened to fit the clapper assembly, and then retightened into the hinge pin after the clapper assembly was pushed firmly home, thereby holding the clapper in place. .... see photos ...
Clapper assembly detail
Clapper assembly plus bell handle
The finished eight