I made some slow progress with my crank jig this weekend. I wanted to make something that would work with both CB, CL and CA cranks so it had to be reversible and that meant some really accurate work to get the holes lined up. I made a drawing of whet I wanted and double checked all of the dimensions.
The only option I haven't covered is the early Dream crank which had 25 mm crank pins compared with all later ones which were 26mm.
The milling machine would handle accurate spacing between holes but I marked out the material just in case I made a mistake in traversing the milling table.
It was then time to load up the two pieces of my jig and drill and accurately bore three holes. Th two outer ones for some steel alignment columns and the middle (actually offset 27 mm which is half the 54 mm stroke) one to take the crankpin.
My little miller struggled with that 25mm thick plate (x2) but eventually we had 3 accurate holes.
I was mightily relieved when I rotated the top plate through 180 degrees and the parts all lined up. Two outside guide pins and two crank pins offset at 180 degrees. Very satisfying.
There wasn't enough ground steel bar for two complete guide pins but here is a 'trial assembly' of the jig with the flywheels and centre pin.
There is still a fixture to make for aligning the cam sprocket but that shouldn't be quite so tricky.
G
