Part 14 by Jason Ballamy

Flywheel and piston

I used one of the 8" flywheels available from RDG as they are very reasonably priced. The surface can be a bit iffy but as I was going to paint the rim that was nothing a bit of filler could not sort out. I held it in the 4-jaw and got the inner surface of the rim running as true as possible. As there were a couple of inclusions in the surface I opted for my insert hold that uses the other two corners of the CCMT type inserts as they are a bit more robust and I have lots of unused corners, this needs to cut from the inside out.

I used the same tool to do the outside of the rim, it would not quite reach the full width but as the casting was a lot wider than I needed that last bit will come off when the other side is done.
Finally the outside of the hub was cleaned up and the central hole bored, also did a bit of cleaning up on the inside of the rim with a rounded tool. Before machining the other side of the flywheel.

Many full size steam engines have hollow cast iron pistons but in our smaller sizes its often easier to make a solid one so to compensate for the increased mass. I like to make my pistons from aluminium. A suitable piece was turned down until 0.010" overside and drilled & tapped for the piston rod. I then cut two grooves for the rings allowing for the oversize piston before parting off.

Once screwed onto the rod and fitted with a locknut the rod was held in a collet and the OD of the piston skimmed down to finished size which made sure it was concentric to the rod if the threading had gone a bit off.
Most of this engine is painted and I had thought about breaking this up with some wood lagging to the cylinder but in the end decided to stick with metal as thats whats in all the photos of preserved pumps.

A suitable sheet of 0.8mm ali was held between two bits of MDF to support it and a strip cut off, by tilting the saw I could cut the full depth of the sheet.

This was then clamped between two bits of flat bar and the two long edges machined straight and parallel.
I then bent it by hand around ever decreasing dia formers (that’s anything suitable and round) until it was a nice fit on the cylinder. The ends were trimmed to length and then the cladding was clamped in place while the 10BA screw holes were drilled & tapped.
With those all done the final job was to drill clearance holes for the drain cocks which was done using a step drill as these give a nice round hole in sheet material and don't tend to snatch.
A few 10BA brass roundheads were trimmed to length and that’s the last bit done.
Next time - painting. The conclusion.