< Smokebox >
The smokebox shell was made from a seamless
brass tube. As the I.D. of the tube is slightly
larger than the O.D. of the boiler barrel,
the tube should be cut an inside step. Two
cherry wood disc and an arbor were employed
to chuck the tube between the center of the
lathe.
There are many holes on the smokebox, for
chimney, blast pipe and steam pipes. They
were bored in the lathe by drill, boring
tool or end mill. Especially the last one
is vital to bore slantwise holes. I marked
out also opposite side of the hole for lining
up between two centers in the lathe.
The smokebox door and the ring are made from
gunmetal castings. The ring is easy turning
job because it has no "hinge lugs"
cast on. Its O.D. is turned to a hand push
fit to the smokebox. On the other hand, the
door is thin and curbed item which requires
careful turning as follows.
Chuck the spigot, turn the sealing face,
saw off the spigot and reverse in the chuck.
Then face off the boss and drill through.
Next, a jig to hold the door is prepared
and the curbed surface is finished with tapered
turning and finally with a smooth file.
The door hinge straps were made from BMS
square bars, soft-soldered onto a piece of
other square bar. Chucking the bar, mill
the steps, file around the bush and drill
through. I left the strap part of the hinge
slightly tapered, because I know a rapid
door opening should bend a thin straight
hinge easily.
The straps have to be bent to fit to the
door surface. It was hard job because the
straps were very tough! I did this with annealing,
pressing and hammering many times. The holes
for the rivet must be opened after the bending,
otherwise the strap is folded at the holes.
Incidentally, distortion of iron rivet head
can be eliminated if you use copper block
as anvil.
The brass hinge lugs were screwed from the
backside of the door ring and silver-soldered.
At the stage, the holes were not opened yet.
Parts for the door handle. The handles and
dirt were made of free-cutting stainless
steel.
The square hole in a handle bush is cut as
shown in the photo; in every 90 degree turns
in the chuck, a half-round cutter is moved
to and fro by hand.
The dirt, which consists of 4mm dia. stem
part and 8mm width triangle part, was made
from 8mm dia. round bar. First, the screwed
part and the square part were finished. For
the latter, the bar was hold in a tool post
and end-milled, with a square bush (like
an axlebox) glued onto the bar for index
rotation with a try-square. Then the opposite
end for the triangle is milled to 4mm thickness.
Next the thinned part was chucked in the
four-jaws, the tip supported by tail stock
center, and the reminder was turned to 4mm
dia. Finally, the triangle's taper is turned
and finished with files.
Now the handle can be used to fix the door
onto the door ring, so as to drill the hinge
lug through the hinge holes.
The brackets for the draw bar, made of brass,
were screwed onto the door ring and silver-soldered.
Then the smokebox door assy was completed.
Due to the modification of the chimney, the
casting can be used only for the base of
the chimney. The chimney body will be made
from a brass round rod and silver soldered
to the base.
The casting was partly finished and parted
off. Note the inside step turned for the
next process.
I used a brass disc fitted to the inside
step so as to fix the casting onto the angle
plate. Then the back surface was fly-cut
to the outer diameter of the smokebox. It
is important to line the miller spindle to
the casting center, otherwise you will get
tilt chimney !
The chimney body was partly turned and silver
soldered to the base. The previous inside
step is useful again to prevent the melted
solder spread over the back surface of the
base.
Finishing the profile in the lathe. The large
radius at the joint was cut step-by-step
and finished with a home-made cutter, a simple
tapered disc parted off from a carbon steel
bar and hardened. Incidentally the inner
hole was cut with a long boring tool from
both side of the chimney.
Filing the base to a correct shape. Note
the protecting tapes around the chimney body
and the tail stock. Finally the base was
cleaned with an emery cloth and a brass wire
brush.
Bush for the chimney fixed in the smokebox.
Note the small tapped hole in the side to
fix the chimney with a screw. The screw's
tip is tapered and the chimney foot has a
groove for the screw. The position of the
groove is a little higher than the hole.
Then, tightening the screw, the chimney is
pulled downward.
The curved surface of the bush was turned
in the lathe as shown in the picture. Again,
the lining is important.
Now the boiler is picked up again. It needs
expansion angles onto the both sides of the
firebox. They were fixed with brass screws
and coke with high melting point soft solder,
because I don't want to have a silver solder
trouble on the boiler any more! Once the
boiler is coke with soft solder, you cannot
silver solder anywhere and also cannot pickle
the job. Because the soft solder is corroded
by acid.
I did a hydraulic pressure test again. In
this time I successfully raised the pressure
up to 1.5 MPa without any leakage. It sounds
easy but it was really painful time ! Incidentally,
a stop valve between the hand pump and the
check valve is useful here. It prevents backward
flow and also you can remove the hand pump
without dropping the pressure. A dental mirror
is useful to check the inside of the firebox.
The smokebox saddle is made from a gunmetal
casting. The top surface was fly-cut in the
same way as the chimney's base. The width
of the saddle was finished using one of the
frame stretchers as a gauge.
The saddle fixed onto the smokebox with screws,
the boiler inserted to the smokebox, then
the whole job is mounted between the frames.
Keeping the frames and the boiler parallel,
it makes shallow countersink onto the saddle
through the holes in the frames. I did this
work with a powered hand drill. Note a copper
tube around the drill as a "stopper".
Then the saddle is removed, drilled and tapped
for assembly.
The smokebox was completed, even though it
contains nothing inside...
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