Once the strap was complete it could be used to gauge the size of the eccentric. After facing and turning to the required OD a small parting tool was used to create the central ridge, which stops the strap moving sideways, first by plunging and then by moving sideways with shallow cuts.

The size was adjusted until the strap would fit but not bind when tightened together.

I then used the height gauge to scribe the offset centre before punching the intersection and then setting the punch mark to run true in the 4 jaw so the hole for the crankshaft could be bored.

After drilling for a grub screw the eccentric could be mounted onto a stub of bar so that the boss could be turned down to finished size.

A piece of bronze was machined square and then the two holes for the guide rods reamed, piston rod hole drilled and tapped. A hole for the cross head pin was drilled and reamed at right angles.

The guide rods are just pieces of 5mm silver steel drilled and tapped M3 at each end and require carefully turning to the same length. They are held to the cylinder cover by CSK screws from below and studs and nuts through the brace at the top. A quick test before shaping the crosshead and all seemed well with it moving smoothly up and down the guides.

The top bracket was cut from some 5mm flat bar to a shape that pleased my eye, a lot easier than bending one up as per the Stuart design. Here it is having the last two holes drilled for the studs that will hold it to the columns.

To ensure that the top brace was in the correct position slots had to be cut into the tapered part of the columns. To do this I first clamped a straight length of bar to the mill table and clocked it true. Then packed the smaller top end of the column both up and away from the straight edge so that it's axis was true along the mill table. It was then just a case of milling a 5mm slot and drilling and tapping for an M3 stud.

The cross head can be shaped however you like and will in some ways be limited by the available tooling if not your imagination, this is what I went with which was done with a mix of manual and CNC mills. Both this and the eccentric will be bead blasted to give them a nice satin look.

Part nine here   Part 11 here