JOWITT MKII POPPET VALVE STEAM ENGINE

By Jason Ballamy - Part three

Click on drawings to download - for personal use only.

Cylinder


Probably the most involved part on the engine. If you don't feel up to it then the curved top and sides could be left square so you have a + shaped cylinder or even just leave it as a rectangular block.

I used and have shown Metric Fine threads on the drawings but ME 40tpi or even standard Metric Coarse could be used if you don't have the fine series taps & dies

The cylinder can just be got out of a piece of 40x80 cast iron bar as it comes out a little over these nominal sizes. I started by sawing off a lump with enough allowance to clean up to the required 64mm length.

Next the top and bottom surfaces were cleaned up on the lathe taking similar amounts off each to reach the 36mm finished thickness.
Then over to the mill to take a light cut off one edge.
Then rotate the work 90 degrees in the vice and using a square make sure the first edge is true, a light behind helps to see any gaps. Once set the second edge can have a light skim. followed by the other two to bring the block down to size.
Mark the position of the bore in the middle of one end and punch.
Back to the lathe and set the punch mark to run true in the 4-jaw using a sprung centre and dti
Using a standard right hand tool the spigot was roughed out.
Then completed with a round nose tool to give the 1.5mm internal radius, the punch hole saw also enlarged with a spotting drill.
And then starting with a 6mm bit progressively opened up to 22mm with a range of drill bits.
This allowed room for a sturdy boring bar to fit and take the bore out to the 24mm diameter finished size.
Then lightly chamfer the corner so the O rings don't get damaged when fitting the piston.
With the main bore in place next we can start to put some shape into the block. Starting with a newly purchased roughing mill from ARC the majority of the waste was removed 7.5mm tall and 3mm per pass.
And then with a 3-flute cutter finished to the required 8mm depth and 46mm width