The last major component is the con rod. As I have changed the crosshead design there will be no need to make the ‘tuning fork’ shaped one of the original which had to be shaped that way to clear the extended piston rod. There are a few options for con rod designs but I decided to keep to something fairly simple and came up with a rod that is not too far removed from that found on other Stuart engines like the Beam and Victoria.

Starting with an over long length of 16 x 16 black (hot rolled) bar which was pickled for a while in brick cleaning acid to remove any scale I set it up in the mill vice and brought it down to the maximum size rectangular section needed to get the part out of. I flipped it over a couple of times to take equal amounts of opposite sides so that it remained straight.

After reducing the areas around the big end (right of image) and the small end (left of image) to their overall rectangular size I spotted, drilled and then reamed the two holes. I have left some excess to the left which will allow me to hold it for turning, this gives a more solid setup than turning between centres and means the interrupted initial cuts don't seem to knock as much plus you can take heavier cuts to get it down to round. You may be able to make out an angle plate  (mounted at an angle) on the right, this was used as a stop to maintain position in Y as the part was turned in the vice.

With the rod rotated 90deg in the vice I then milled a slot which will form the forked end once the chucking material has been removed. I've clamped the end to another angle plate just to make sure the overhanging end is as rigid as possible so there is less chance of any cutter chatter.

With the job now held in the 4-jaw chuck and supported at the other end with a revolving centre it was turned to the largest diameter of the ‘fish belly’ and then a Sharpie used to mark approx 1/3rd in from each end. You can also see that I have left the rectangle section at the crank pin end a bit longer than the Stuart ones so that I can put in two dummy strap bolts rather than one.

The top slide was then set over a few degrees and one end tapered followed by setting it the opposite way and tapering the other 1/3. I use an insert with a 2mm dia end so that a nice fillet was left in the transition from round to rectangular. All that remained was to blend the three facets with files and then emery to get a smooth looking fish belly shape to the rod.

Having the extra SX2.7 mill in the workshop I tend to leave the ARC rotary table and chuck on that so it's a quick setup to mount anything that needs rounding over on one of the many arbours that I have built up over the years and round the ends on the mill. here I have a sacrificial washer between arbour and work so the cutter can have its end just below the work and the M8 nut at the top is unlikely to be much use for anything now but I've got a big pile of them. Rounding was done with full depth cuts, 1mm step-over for the first few and then reduced to 0.5mm once the nut started to get cut too.

The forked end was rounded in a similar way after sawing off the chucking piece and then just a bit of file work to blend the outside of the fork into the round rod and get the fork to look U-shaped.

I'm a bit of a fan of aluminium pistons in engines both I/C and steam as they do reduce the reciprocating weight so starting with some 1" 6082 bar, the end was faced, spot drilled, drilled tapping size right through and then counter drilled 5mm (piston rod size) for about 1/3rd the piston thickness before being tapped M5 with a spiral flute tap.

After sawing off a length the sawn surface was faced and a counterbore turned so that a lock nut can be used on the piston rod but not hit the cylinder end cover.

Well that covers all the parts I took specific photos of but there are a few others which luckily seem to have all migrated to this corner of the group photo.

Part ten here   Part 12 here