A similar situation I found was that the diameter of the cylinder cover did not match
precisely that of the standard. Whilst probably no more than 1 thou it was proving
a long job to match the two items and polish then using just emery paper with the
assembly stationary. I decided therefore to make a tapped stub mandrel using an M3
thread and a 5/32” stub then the two parts were held together with a couple of 7BA
screws and secured on the mandrel with an M3 screw and a large washer. The two flanges
were then very lightly machined followed by polishing, see Photograph 71. I think
the photograph shows that the result is better than could easily be achieved manually
and made the time spent making the mandrel (probably no more than 10 minutes) very
worthwhile, in any case, it probably saved more than the time that it would have
taken to complete the task manually.
When polishing parts whilst they are running in the lathe do take extreme care so
as to avoid any accident, try to use a long strip of emery paper backed by a long
file so that ones hands, and the ends of the file, can be kept well clear of the
With cast brass parts these should have the evidence of them being cast removed with
suitable fine files and then, together with the machined surfaces, brought to a bright
finish using progressively finer grits, and finally finished with a brass liquid
polish, “Brasso” typically.
Tip Do not think that you have finished with the taper stub mandrels as they can
at this stage now be used in the bench vice becoming an excellent method of holding
some of the parts for finishing, see Photograph 72. Also when painting the flywheel.
First give the required surfaces a primer finish followed by two coats of the chosen
colour. Leave each colour for a few days so that it fully hardens and will then allow
the surface to be lightly sanded with a fine paper to remove dust particles, etc.
and provide a good surface for the next coat. With the final coat you will not be
able to sand out unsatisfactory areas so do pay particular care with this stage.
I use Humbrol modeling paints which I have found very easy to use. Unfortunately
though, they appear to have changed to a different formulation but when I discovered
that it needed much more mixing prior to being used it worked quite well, though
I did prefer the earlier mix that would for some applications be OK with just one
Stuart, the suppliers of the castings, do supply paint that they state is “steam
proof” but is only available in two colours, a dull green and gloss black. I normally
use Humbrol Emerald no.2 but chose to use Brunswick Green no. 3 for these two engines
so that they stood out from the ones I have already made.
Forming the Cylinder Lagging
This operation needs to be done with care as if unsatisfactory when formed it will
not be easy to make any changes to improve the situation. A major requirement of
this stage is to avoid the edges of the lagging from showing as whilst the face
is black anodised the cut edges are still plain aluminium and will be very prominent
if not obscured by the adjacent parts.
First, freely assemble the cylinder covers to both ends of the cylinder and check
that it is sufficiently below the outer diameter of the covers so that the edges
of the lagging will be concealed when finally assembled. If not then carefully file
around the edge of the cylinder to lower it slightly and recheck. Do take into account
that the lagging will not fit perfectly against the cylinder so the difference between
the cylinder and the covers needs to be rather more than the thickness of the lagging.
The next check is to add four studs into the tapped holes in the rectangular face
and place the valve chest over these checking that the edge of the lagging will be
hidden. If not then file the sloping edge of the cylinder so as to achieve the required
result. Do not just file the edge locally but make sure the slope is continuous from
the curved end of the cylinder down to the edge that mates with the valve chest.