Piston Rod 5
Crosshead Pin 52
Valve Rod 21
These are relatively simple turned parts, all made from 1/8” diameter steel. The
threads should be made using a tailstock die holder, rather than a hand held die
stock, as they must be axially in line. Concentricity is also important and it would
be best to use the four jaw chuck so that the material can be set to run true, especially
for the piston rod.
The drawing for the crosshead pin does not show that the end requires a slot to take
a screwdriver, a requirement that you will soon find out when you come to assemble
the engine. This can be achieved with a hand held hack saw but this rarely works
for me, appearance wise, and I suggest you mount the pin on the lathe top slide
and make the slot using a slitting saw. To position the saw centrally, touch the
side of the part with the side of the saw. Then, move the part forward using the
cross slide and move it sideways by half the saws width plus half the parts diameter
and make the saw cut.
This is provided with a stub, rather like the con rod, see photograph 44, which can
be held in the three jaw for machining. Machine the outer diameter which needs to
be a close fit in the standard, face the end, drill and tap 5BA, and part off at
just over 7/16” long.
Assemble with the piston rod and holding the rod in the three jaw with the crosshead
firmly against the chuck's jaws carefully face the outer end to 7/16” long. Mark
out and drill the 5/32” hole.
Mount the piece of 7/8” brass in the three jaw and turn the outer diameter to a close
fit in the Cylinder. Face the end and drill and tap 5BA, make the oil groves with
a pointed tool and part off at a little over 1/4”. Assemble with the Piston Rod,
place the rod in the three jaw and with the piston against the chuck jaws face to
Piston Gland 8
Turn the outer diameter, make the thread, drill 5/32” and part off. Note the substantial
chamfer into the drilled hole, do this using the centre drill deeper than normal.
The part now needs six recesses made around its circumference, fortunately, much
easier that the five required with the cylinder. With a short length of hexagonal
material in the three jaw, face the end and drill and tap 5/16 x 26TPI, remove, fit
the gland and mount on the top slide with a fence for guidance, the fence is just
visible in Photograph 57. Add packing below the hexagon to bring the gland up to
nominally centre height and with a 1/16” end mill running at the highest available
speed make the recesses, using the hexagon to index the part for each one.
The fence is held secure with a nut on the top slide stud prior to the clamp being
added and therefore remains in place for each of the slots being made.