MONITOR ‘BALL HOPPER’ HIT N MISS ENGINE

Part 3 - large crankshaft by Jason Ballamy

The crankshaft started life as a rusty lump that had been flame cut from a piece of 1" hot rolled plate, there was some hard scale on the surface particularly the cut edge and by the time I had milled the four sides down to size I had three blunt corners on my 40mm indexable end mill.

With the four sides complete it was milled to length and some basic layout done, I then held it vertically on the mill by clamping to an angle plate and located the edges.
From these datums the positions of the centre holes were located and drilled.

Using a 1/4" split point stub drill the waste was stitch drilled away spacing the holes at 0.250" so they just joined together.

It just needed a small saw cut where I had kept shy of the vice and the waste dropped out.
Before starting on the journal I like to rough out the rest of the shaft so it is a bit more balanced when cutting the journal.
The tapers are to give the back of the tool clearance, these were then removed by turning the crankshaft end for end.
Then using the other pair of centre holes to turn the journal, inside faces of the webs and the small chamfer to the edge of the web.
The excess material was sawn off the ends, a close fitting spacer wired and hot glued in between the webs to stop the tailstock pressure distorting things and the main shaft turned to 5/8" finished dia, final job was the other two chamfers on the outside of the webs.
Job done!