As discussed in the last post, I decided to remake the bearings as drawn/described from a solid Phosphor Bronze (SAE 660 aka Gunmetal) block – being as how I had needed to remachine the crank journals after assembly, and the first set of fabricated bearings were a bit “naff”..
So the first job is to cut the block in two (longitudinally) clean these two pieces into neat cuboids, and then soft-solder them back together for machining.
This time I decided to machine the bores first, and then mill the seatings for the housing by measurement from the bores – in this way you would be able to “guarantee” that the resulting bores all lined up!
Much more success!
One of the problematic things was how to measure the distance from the bore to the outer facing – this would need ball-faced micrometer, not something I had. After some thought this idea occurred: by hot gluing a ball bearing to the anvil (and remembering to subtract the diameter of the ball from what I measured) everything would be fine – and it was!
- Home made ball-headed micrometer (ball bearing hot glued to anvil)
So by first machining the back face of the bearing housing, and the bottom of the bearing housing to the correct dimension from the bore we knew that things would line up. Then the forward face could be machined to be a snug fit in the housing.
Lastly the top surface was machined to ensure the bearing keeps would provide a little “crush” when tight.
I cut everything to allow for a little hand-finishing (to make sure there was no slop), and then unsolder the two halves, clean up and try them on the journals – they were too tight!
But this was “kind of what I had planned”, so then fitting the bearings in place, and a few hours with the engineer’s blue and hand scraping we wound up with a crank fitted and turning pretty freely. (this description skips over the machining of the ends of the housings to provide for the correct end float, which was a bit “trial and error” – but all came out OK.
A slide show of the process…