Cylinders

The cylinders have been bored to size (two inches in diameter) and the steam passages have been drilled and milled. Mounting holes for the end caps and valve connections will be match drilled when those parts are made.

My first attempt at machining the cylinders was to mount them in a four jaw chuck. I was afraid there might be too much vibration on the outboard end and that proved to be correct. Two other problems became apparent with this setup. First, the 1/2 inch boring bar was not robust enough for a five inch bore. I could see it flexing as it got closer to the chuck. The second problem was alignment. I started boring at an angle. Fortunately I caught the problem before it was too late to correct.

I made a new boring bar out of 1-1/8 inch diameter steel with a crbide insert mounted on the cutting end. I built a fixture on a face plate allowing more stability and accurate alignment. The aluminum plate was bored to a close fit with the end ring. Adjustment screws on the protruding blocks, allowed me to use an indicator on the outboard end ring for close alignment.

This closeup shows the insert starting a cut. I took off 0.020″ per pass for roughing at a fairly fast feed. Finishing passes were very small with a feed of 0.002″ per revolution.

The side of the cylinder where the connections to the piston valve will be made was milled flat and stoned for a smooth finish.

Three holes 3/16″ in diameter were cut in the end for steam passages. Three holes were cut at ninety degrees to intersect the end holes. Care was taken to not drill too deep. I measured the depth of cut often.

I used end mills to make a 5/8″ diameter counter bore to encompass the three side holes on each end of the cylinders for flange connections.

Finally, I milled a pocket over the end holes to allow steam to enter the end of the cylinder.