Simple Oscillating Steam Engine - Piston Assembly

The piston was made from brass and included the connecting rod and bearing assembly.

Click for larger drawing









A piece of bar slightly larger than the required piston diameter was placed in the chuck. It was left sticking out the equivalent of the cylinder length.









The parting off tool was used to reduce a section of the bar below the piston.









The piston was then turned slightly oversized or until it was a very tight fit in the bore.

Ideally a piston hone should then be used to smooth out the machining marks on the piston. A cheap substitute is some very fine (2500 grit) paper supported on a flat edge such as a file.

Care was taken to ensure that the piston remained parallel. Fine sanding strokes were used until the piston was a snug fit in the cylinder. Then it was deburred gently to finish.










After the piston was finished the rod was pulled forward in the chuck to allow the piston rod and 'big-end' bearing to be tuned. The material below the piston was removed to a diameter of 8mm.









Next the connecting rod was turned to a diameter of 5mm.









Before the finished part was parted from the bar it was removed from the chuck and marked out for the crank pin hole.









The additional length of bar enabled the piston assembly to be clamped in the Vee block and drilled in the pillar drill as shown.










Finally the work was replaced in the chuck and parted from the bar. As usual the tool was retracted part way through so that a file could be use to chamfer the bottom edge.











The finished piston assembly