|Saddle HM406: The center
part of the saddle is made from a 9.25" length of 1.75" X 2" steel
bar. The top edge of the saddle slopes down on each side.
I was able to cut the slopes on my little band saw as shown in the
photo at right. The saw made this task easy.
|The next step was to saw the notches for the fame
bars on each end and then use the mill to finish the cuts and the
slopes to the
exact dimensions. The upper surface was then smoothed on the
belt sander to remove the milling marks. This was also easier than
|The next step was to cut the sides from 9.25"
lengths of 3/16" X 2" bar stock. The pieces were rough cut on
the band saw and then finished to dimension on the mill. The
sides were attached with four 4-40 FH brass screws per side. The screws
are only partially countersunk. After the sides are silver
soldered to the center the screw heads will be filed off.
Enough of the head remains to hold the sides in place if the jointed
are reheated. On the other hand, enough of the head sticks out
so that when smoothed, the screwdriver slot is removed.
|The next step was to machine the
4.25" radius in the top of the saddle. I used the setup shown
on the right. There are spacers under the saddle to hold it
off the table. The tool speed was set very low (~100 rpm) and
small cuts were taken (~0.01"-0.02"). This was the second
dreaded task in making the saddle and it went very well.
|The next step was to cut the smoke box base from
the 1/4" thick 8" OD tube stock that will be used for the smoke box.
The OD of this piece should be 8.5" diameter to mate with the smoke
box. I put the piece in an hydraulic press and flattened
it slightly so that it fit perfectly with with the smoke box tube.
(I actually bent it a bit too far and had to press it back slightly.
It's harder to bend back so it's best to do this operation very
|The next step was to make the exhaust port pieces.
These pieces mate with identical pieces soldered to the exhaust
pipes so a total of four pieces were machined. The pieces were
cut from 1/8" plate. The plates have a 3/4" center hole and
side holes made with a #33 drill. I drilled the side holes in
one piece and then stacked the four pieces on a 3/4" expanding
mandrel and used the holes in the top piece as a pattern to
drill identical holes in the other three pieces. A pair of
4-40 screws through these holes with nuts on the back hold the four
The next step was
to turn the 1.125" diameter side edges. This was done on
the mill using the setup shown on the right. That's a 5C
collet holder attached to the rotary table. The
side of the end mill was used against the sides of the plates as the rotary table
is turned. Worked neat.
|After the sides were finished on the mill, the edges
around the screw holes were smoothed using a file and a sanding drum
on a Dremel rotary tool. The finished pieces are
shown on the right.
Unfortunately, shortly after removing the rotary table from the
mill I realized that four more of these pieces are needed for joints
in the exhaust pipes near the cylinders. I leave that
collet fixture attached to the rotary table so it won't be difficult
to set it up again.
|The next step was to attach the smoke box
base to the rest of the saddle with a 1/4" FH screw. The 3/4' diameter holes were then
drilled for the input ports on the side and the output port in the
center. The side holes are drilled perpendicular to the
sloped sides. A short length of 3/4" rod was used to position
one of the port plates as a pattern over the input ports to drill the side screw
holes. The screw holes were drilled all the way through
(#36 drill) and the top part tapped 6-32. Stainless
steel 6-32 studs will be screwed into these
holes. Hopefully any broken studs will be easy to drill out from the bottom.
|The passages connecting the side and center ports were
milled next. The passages are 0.75" wide and 0.4" deep Each
passage was milled in two passes.
Note that the sides are held to the center with steel socket head
cap screws at this point. I was concerned that the brass screws might shear
due to stresses from the milling operations. These steel screws were
removed and replaced with FH brass screws before the soldering
|The passage near the three holes were stepped with
the mill as shown in the photo. These steps were then
smoothed with a rotary tool. Sorry, forgot to take a photo
after the smoothing.
The sides, curved base and the port plates were all silver
soldered at this time. Two more holes were drilled
in each side for screws and brass screws were used everywhere.
The port plates were also held in place with brass screws.
The parts were all pickled in preparation for the soldering. The
joints were fluxed and strip solder was placed between the surfaces
along all edges. This time I used an acetylene torch to do the
soldering. It was quicker than the propane torch.
|A deflector is needed to guide the exhaust gases
from the horizontal passages up the center hole. The
photo at the right shows machining the end of a 3/4" square brass
bar with a 3/4" diameter end mill. Both sides of the bar were
|The deflector was sawed off the brass bar and
positioned on the base plate so that it will be under the center
hole. It was secured with a single 4-40 brass FH screw. Photo
shows the base plate with deflector. Once the
position of the deflector was verified to be correct it was silver soldered
to the bottom plate. The next step was to solder
the base plate and the angles at the sides to the bottom of the
saddle. Everything was pickled and fluxed and brass screws and
strip solder was used again. This time the propane torch
was used to heat the joints.
Photo above shows the top front of the finished saddle. I
forgot to mention that the holes to attach the smoke box to
the saddle were drilled in the curved base before it was soldered
in place. Several of the brass screws that held the port
plates in position also got soldered in the process.
After all the soldering was finished the screws were drilled out
from the bottom and the holes tapped again.
This photo shows the finished bottom. After everything was
soldered the saddle was tested for leaks using water. There
were a couple small leaks around the base. The
saddle was pickled again, the areas around the leaks fluxed and
pieces of a type of solder made to fill larger gaps (McMaster-Carr
#7676A3) were laid over the
leaking joins and then the joints were heated again. That
fixed all the leaks except small leaks out of the holes at the
bottom of the holes from the port screws. These holes will be
plugged with stainless setscrews.
After all soldering was finished, the saddle was pickled again to
remove any remaining flux. The surfaces were then smoothed and
screw heads removed using the belt sander, files and a sanding
drum in the Dremel rotary tool. The final step was to
bead blast the saddle. It is now ready to paint.
The tough frame parts are finished so now it's on to the easy