Display Model Only?
If you intend your engine to be purely a display model, at least initially, you may
chose to omit the 1/4” x 32 tpi hole above. Also a consideration for the Valve Chest
and the Lagging.
Cylinder Covers 6/15
Start with part 15. With the piece of cast iron bar in the three jaw turn to 1-3/8”
diameter over a short length, face the end and turn the 3/4” spigot, making this
a good fit in the cylinder. Next, start parting off at a little over 5/32” (including
the spigot) stopping short of the 13/16” diameter and wind the parting tool out.
Next set the parting tool at a little over the 7/32” dimension and part off fully.
With the cast bar still in the chuck work can commence on part 6. Turn the boss
but leaving it a little oversize on diameter, do not turn the outside diameter. Remove,
reverse, return to the chuck holding it using the boss, lightly centre drill and
support with the tailstock centre. Part off making the flange about 5/32” wide, removing
the centre when parting off is almost complete. Now face the end and accurately turn
the 3/4” diameter 1/32” deep also turning the 1-3/8” outside diameter. Centre drill
and drill completely though 5/32”, this ensuring that the hole is concentric with
the 3/4” diameter, and remove.
You will see from the included photographs that I am using a rear toolpost mounted
parting off tool being by far the preferred method in most cases. If though you do
not have this facility then a top slide mounted tool will suffice for most operations
providing it is done with extra care. Where I do not consider this to be suitable
I will make a comment to this effect.
Using the drilling machine, pre drill the other side 6.5mm by 9/32” deep. Note, this
is not tapping drill size for the thread to be made, the hole being bored to size
Next, make a fixture, not detailed on the drawings, using a short length of 1-1/2”
steel (or larger) very firmly clamped in the three jaw. Face the end and accurately
bore to 3/4” diameter by 10mm deep. The base of the bore does not have to be flat,
for example, if you used a 1/2” drill to commence the bore the base of the bore can
be left as produced by the drill. Lightly centre drill the base of the bore for use
later. Do not remove from the chuck.
Apply some thin film double adhesive to the rim, making sure it does not overlap
making it thicker in some places, and fix part 15 to this, applying pressure for
a couple of minutes using the end of the tailstock barrel. This was the reason for
stating “firmly clamped”. Then finish machine the part as per the drawing. Note,
the 13/16” spigot is finished with a small radius. Whilst still on the fixture remove
machining marks using emery paper, say 400 grit followed progressively by finer
grades up to 1200 grit.
Next finish machine part 6 using the same approach, typically, thickness of the flange,
diameter and length of the boss, Photograph 20, note that the boss must be a close
fit in the standard. Additionally, bore the pre drilled hole to 0.275” x 9/32” deep
and tap as per the drawing. To do this, hold the tap loosely in the drill chuck and
with the tap holder located in the tap's flute at the non working end, tap the part
by turning the tap holder, see photographs that follow. DO NOT REMOVE THE FIXTURE
FROM THE CHUCK.