Next up is the crankshaft. Starting with the correct
sized steel rod, a hole is drilled in the center of
the crank disc that is .001" smaller than the diameter of
the crank shaft itself. Then the shaft is
held in the tailstock chuck and pressed into the crank disc.
Now the disc and shaft assembly are parted off to a couple
thou over the finish thickness. Then the piece
is held by the shaft end and the face of the disc is cleaned
up to remove the few ridges left by parting.
The piece is then moved to the mill and centered, then offset
1/2 the stroke of the engine and drilled
for the crank pin, again .001" undersized. The crank pin
is then held in the mill spindle and pressed
into the crank disc and finally...
...the completed crankshaft. By using the lathe and mill
to press the shaft and pin into the disc
at the time the holes were drilled, it assures the two are
perpendicular to the disc, and parallel
to each other, which is what is needed.
I had to make the screws that hold the cylinder springs, which
hold the cylinder flat against the
engine standard. These are made from hex stock turned
down to a couple of stepped diameters. One
diameter is to take the #1-72 threads, and the larger diameter
is sized close to the ID of the cylinder
springs. The threads are cut with a split die, opened up at
first to avoid breaking off the thread
shank, then closed down a bit to bring the threads to
That's them. Six little cap screws.
The springs had to be made, since they are quite small and I
didn't hold much hope for finding them
in a commercial size. These were made using a small nail
for a mandrel, and .013" dia music wire.
The music wire in this case is polished guitar string.
Here's an assembly shot of the engine parts, minus the
flywheel. Another little part I didn't show
being made is the small stepped washer seen between the cap
screw and spring. The minor diameter on
this washer fits inside the spring and the screw goes through
the works and into the cylinder pivot.
The step on the washer and the counterbore in the standard
prevent the spring from bulging sideways.
With all of the other parts for the boilers and engines made,
it's time to turn to the flywheels. These
will be 1" diameter, and hopefully, some kind of nice shape.
Starting with brass round stock, I parted off eight round
blanks. There are only six engines, but for
what is planned, I figure there may be a couple of goofs
destined for the scrap bin.
I have full round soft jaws on the chuck, here. The jaws
are made to be cut up for whatever diameter is
needed, and to provide a large clamping surface for thin work
pieces. These are made for my particular
brand of lathe, and since they are considered a consumable,
are pretty cheap. They are $8 a set, and
after you've cut them up enough to be un-usable they get
tossed and a new set put on. I've gone through
a few sets of these.
A tool bit is ground up so that the bevel on the flywheel hub
and the inside of the rim can be cut
without changing tools. Notice that the part of the tool
bit under the cutting edges slopes away
under the front of the tool. Since the tool is plunged
into the work for these cuts, that is needed
to prevent the lower part of the tool from rubbing on the
inner radius of the flywheel rim.
I wanted to make something other than a flat wheel or a disc
with holes, so I did some doodling on
one of the blanks to come up with a shape. Spokes would
be nice. Curved spokes would be nicer.
After finding a radius that looked okay for the curve of the
spokes, I got out some of my old drafting
tools and scratched up some arcs and centers to get some
dimensions and locations for off center
mounting of the pieces on my rotary table.
The rotary table is mounted and centered under the spindle on
the milling machine, then a sacrificial piece
of aluminum plate is mounted directly over the center of the
RT. This aluminum plate has three holes
drilled for locating various features of the spoked
flywheels. The hole at the red arrow has a pin in it
that will fit the center bore of the flywheel. That pin,
and the center of the RT run true under the mill
spindle, and will allow drilling hole circles that run
concentric with the rim of the flywheel.
The hole at the black arrow is an offset, and when the
flywheel is placed over a pin in that hole it lets
the RT rotate the flywheel in a way that allows cutting one
side of the spokes.
The hole at the green arrow is to align the flywheel blank for
cutting the spoke shape. It aids in indexing
the blank to the correct position so the spokes are equally
spaced and the same thickness. That hole is
just a guide, and is only used to help space the spokes.
The other holes and marks on the plate are a result of using
it and cutting a little too deep while drilling
or milling the features of the flywheels. Besides its
use as a jig, the plate also protects the top of my
This picture shows the process of drilling all the locating
holes in a flywheel blank. The holes in the #1
position are drilled first. Then the holes at the #2
position, and then the #3 holes. The #1 and #2 holes
are 5/64" diameter and are the positions of the front side of
the spokes. The #3 holes are 1/16" dia.
They are the position of the back sides of the spokes.
All of these holes are located in concentric circles
off the center of the flywheel.
The number 1 and 2 holes are drilled at 72 degrees
apart. After the last #2 hole is drilled, the RT is
turned 22 degrees and then the smaller #3 holes are all done
72 degrees apart.
With all those hole circles done, the pin is pulled from the
center hole and another pin put in the offset
hole at the black arrow.
The blank is placed over that pin, and a drill bit is used to
position the blank for the next step, then
the blank is clamped down on the RT. (I just hold the
drill bit with my fingers.) The mill table, (not
the rotary table) is repositioned so that when the RT turns it
will cut an arc from the outside rim to
the inside hub between holes 1 and 2.
Now the first arc is cut using the #1 and #2 holes as starting
and stopping points. These are all
cut with a 5/64" diameter end mill
This shot shows the first set of arcs completed.
Now the second set of arcs can be cut. The blank remains
on the offset pin in the plate on the RT,
and the mill table is
repositioned again to put it in the correct position to cut
the next set of arcs.
These cuts are done with a 1/16" end mill. After each
arc is cut, the clamp on the blank is loosened
and the blank rotated so the next starter hole is lined up
with the end mill.
Throughout all of the cutting on the piece, the rotary table
remains clamped to the milling machine
cross slide table in the same position. The only axes on
the milling machine that change are the
mill table itself, and the rotating part of the rotary
table. Hope that makes sense.
This shot shows a blank with the first set of arcs cut
compared to one with both sets of arcs done.
It doesn't take much imagination to see what has to be done
Now the RT is once again centered under the milling machine
spindle and the blank replaced on the original
pin that was used to drill all the holes in the earlier
steps. Then, by offsetting the mill table to the
original diameters of the hole circles, the waste between the
spokes at the hub diameter, then the rim
diameter can be cut away.
In this shot the inside rim looks pretty ragged. I'm
just roughing out the waste pieces here.
Final steps are to increase the diameter of the cuts to the
rim a few thousandths of an inch to clean up
the rough edges, giving a smoother finish. I start these
finishing cuts somewhat inside the final inside
diameter of the rim and work outward until the end mill cleans
up the small original drill bit holes.
I ended up with six good flywheels. If you remember, I
started with eight blanks. On one of them I got
to cranking the RT a little too causally and one of the spokes
is slightly mis-cut. The eighth blank did
not get used at all. I'll save it for another day.
All that's left is to test run all of the engines, do a little
finish work to shine up the finish of the
brass parts that still have some of the discoloration that
comes from the foundry, and pressure tests.
All of the boilers get hydro-tested to 60 psi, which is shown
in the picture above. A hydro-test is a
safe way to test boiler shells, as it will not produce any
shrapnel in the case of a boiler failure. Should
a boiler fail under hydro-test, all that will happen is a
quick squirt of water will come out at the point
of the failure. The boiler may be ruined, but the
surroundings, (mainly, the people), will get nothing
more that a bit wet.
To test these boilers, they are first filled completely full
with water. No air space is left at all. Then
the pressure adapter is screwed in the top and more water is
forced in until the gauge reads what you want
for the test pressure. That is 60 pounds here, and the
boiler is then left for a time interval, such as
a half hour or so. If the pressure remains constant over
the time period, the boiler is sound. If it goes
down, you have a leak somewhere.
It is fairly important to keep the boiler full of water at a
constant temperature throughout the test period.
If the boiler gets warmer or cooler during that period, you
can have a false test. I start with both the
boiler and the water at room temperature, and keep the boiler
at that throughout the test. That is fairly
easy to do indoors, since it is not likely that the room will
change temperature enough to affect things.
If the temperature goes down a few degrees, the test will give
the impression that you have a leak, since
the pressure will go down.
Here they are, all boilers pressure tested and all engines
Below is a video of one of the running Tripod Steam Plants.