The Bearings
  • Hi,
    I'm getting ready to fit the bearings to the arbor and I have a question. The arbor isn't a press fit into the inner race is it? If that's the case then the bearings don't really act as bearings do they? The inner race acts more like a bushing. The arbor as it revolves in a complete circle just rubs against the bottom of the inner race. The inner race itself wouldn't revolve unless the frame sagged and the arbor bound [binded?] in the inner race?
    Thanks,
    Mark
  • That's the one I am thinking. The bearing will still rotate with the arbor even if it's not press fitted, it's just not efficient. I used to assemble a lot of RC toys, and the number one rules in assembling gears is making sure bearing and shaft are fit together without any play to utilise the bearing efficiently. If that's the case we need to mount the bearing in the gears and not in the frame. Mounting the bearings in the frame I think will work but we need to make sure arbors and bearings are properly aligned.
  • I have just finished my Sextus (it's been sat on the shelf as an untouched kit for a couple of years but I'm glad I waited till I had time to give it the attention it deserves). I think the most useful thing to do regarding the bearings is to wash the grease out of them. This took quite a time with repeated immersion in white spirit followed by wicking the spirit/grease out by pressing the bearings down on a kitchen towel. When the circles on the kitchen towel dried without leaving a stain I reckoned I'd got most of the grease out. I checked my progress by threading the bearings on a shaft and spinning the outer with a flick of my thumb and by the time I had finished the spin time of the outer was about 6 seconds (the best result I got was with some lovely little 2 x 5 x 2.5 bearings from a model helicopter that when washed span for 15 seconds! - I'm going to use those in a clock when I can)

    Anyway, the result is that my Sextus pendula swing for about 150 seconds - way longer than before the bearings were washed and it runs (albeit slow) with only a 1.6kg weight.

    As for the fit to the shaft, I don't see there is an issue. With the bearings being so free I'm sure they will turn and the shaft will just be in rolling contact with the inside of the race. In some ways this is not unlike the situation you have with anti-friction wheels (as per a Robart high-point propeller balancer) where the shaft rolls on the surface of the wheel.