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3 Sisters Engine
Here’s an interesting 3
cylinder oscillating-type engine that we made using modified plans from the
Jingle Bell Motor (seen elsewhere on this site). The most difficult-to-build
part might be the CNC-produced flywheel (but a simple round one of the same
diameter and built from plywood, would work fine......there’s also a
“straight-bar” alternate flywheel shown among the drawings below). The two “T”
connectors and plastic hose are aquarium supplies. Crank is pressed together
(you can slightly “under drill” (by about .001” or .002”) the holes and press
the main shaft and crank pin into place using a good vise (or an arbor press, if
you have one). Drill or ream the cylinders to a very smooth .25 diameter. Turn
down the brass pistons to about .260”..........then use a file or emery paper on
a lathe to finish them to size, using one of the cylinders as a gauge (when the
piston just fits, you’re done). This finishing process is best done on a
lathe, but I’ve successfully done it by chucking the piston into an electric
hand drill.
 
(Above) Pistons are
“staggered”, one behind the other. This is possible because each of the cylinder
“Standards” has a different step at it’s attachment point to the main bearing.
(Above) Engine is
mounted on channel aluminum (anything similar would work fine).
(Above) “Rear” view,
showing hose “T” connectors and flywheel. Flywheel is held between two nuts, and
is easily removed. The small hole in the back of the Standard (seen in the right
side of the picture)is the exhaust port. The larger hole near it is the 10-32
threaded hole for the pivot bolt.
Hardware Store Steam Engine
All of
the materials needed to build this engine can be bought at the hardware store
for under $10
Instructions For Construction
Disclaimer
Use all recommended safety measures and safety equipment to prevent injury
Persons under 18 years of age must use adult supervision.
Bushing
The bronze bushing can be cut in half, half will be soldered onto upright and
other half will be placed in center of flywheel. The half that is to be set in
flywheel needs to be drilled and taped to lock it onto the crankshaft. These
bushings are saturated with oil, the half that is to be soldered to upright
needs to be heated with a torch to remove oil before soldering can be done. Use
a small flame – a lot of smoke came off of it and it may catch fire for a
moment,( best done out side).
Measure mark and punch a spot 1/8” from the end.
Drill 7/64” hole
Tap to #6-32
Flywheel
The flywheel is the valve handle.
Drill the center of the handle to 3/8” – The hole in the one that I used came
square to fit onto a valve stem. You can step up one drill size at a time, to
maintain a better centering in the handle. The handle was also cast iron,
Drilling should be done slow as not to crack handle.
Set the half of bushing (which has been drilled and taped) into the hole in the
middle of handle. Leave the taped hole exposed, so a screw can be turned into
taped hole. The bushing can be set into flywheel with epoxy or supper glue.
Upright
Cut upright from brass strip- file both ends true. Lay out for the holes, needs
to be done very carefully. Do all lay out before drilling any holes. Mark holes
with a center punch, awl or sharpened nail. Measure from bottom for all layouts.
Measure and mark ¼” up and 3/16” from each edge for base screw holes.
Measure and mark 1 3/16” up and on center for crankshaft hole.
Measure and mark 2 1/8” up and on center for cylinder pivot hole.
Scribe a line across upright at center of crankshaft hole and mark ¼” from
center on both sides of crankshaft mark. This is for valve hole lay out only, do
not drill.
Lay a straight edge from these marks up and across cylinder pivot hole mark and
scribe a line up about ½” up from cylinder pivot mark. This will form a V mark
from the cylinder pivot point up.
Now measure from cylinder pivot point up each line and mark at 3/8”, mark and
punch. Now spot drill all holes to 1/16 and then enlarge holes to size as
indicated on plans.
Solder the crankshaft bushing to the upright by first cutting a piece of the ¼”
aluminum tube about 1 ½” long. This will be used for aligning bushing with the
crankshaft hole in the upright. Flux around ¼” hole in upright and the factory
end of the cut bushing. Slide aluminum tube through upright hole and then slide
bushing on till bushing seats to upright. The aluminum tube will align the parts
and then can be slide out after soldering is done. The face of the upright can
be lightly sanded, to insure flatness, by laying a piece of fine sandpaper on a
flat surface and sliding the face of the upright back and forth.
File 45% on top corners and half rounds near base, as to the plans.
Angle
Cut 1 1/8” piece from the brass strip to form the angle, mark at bend – place
between two smooth blocks of hard wood or other scrap metal plates, place in
vise and bend. File to true up both ends and file 45% angles on all corners.
Align bottom of upright to angle and drill both holes though both pieces with
7/64” or #36 drill to insure alignment. Separate the two pieces and enlarge
holes in upright to 5/32”or #25. Tap holes in angle for #6-32 screws.
Base
Cut 2 pieces of the brass strip 2” long. Sand or file(to remove the finish) one
of the edges of each piece to be soldered together. Flux the two sanded edges
and place side by side – flux bottom of angle and place on top of base pieces.
The upturned part of the angle with the two holes in it should be 5/8” from end
of base and turned 90% to the joint in the base. Now heat and solder all three
together. After the pieces cool, file ends of base true and file 45% angles on
all corners, drill a1/8” hole on ether side for mounting and sand any excess
solder off.
Crankshaft
Cut the head off one of the rivets, this will be the crankshaft.
Cut a piece from this rod that is 3/16” long and set aside, this will be the
cylinder plug.
Cut a piece of the brass strip ¾” long, for the crank end, find the center, mark
and punch, use a compass to draw a 11/16” circle – do not shape till holes are
drilled.
Now measure over1/4” from center and mark and punch. Pre drill both holes 1/16”
and then enlarge the holes to the sizes on plans.
File circle to mark.
Cut a piece of 1/8” brass rod 7/16” long.
Sand and flux the end of steel crankshaft and place in center hole of circle,
flush with end of rod.
Sand and flux and place 1/8” rod in other hole, (from other side), flush with
end of rod. Make sure both are as straight as possible. If ether rod is lose,
tap edge of hole with punch to move some material into hole and try fitting
again.
Heat and solder when both are aligned.
Piston
Cut the other rivet head off to leave a piece of the rod that is 1 5/16” long,
file the cut end true.
File flats on rod as shown in plans.
Measure, mark, punch and drill 1/8” hole in flat end, 1 1/8” from head of
piston.
Cylinder and Plug
Cut a piece of the 9/32” brass tube long enough to be trued up to 1 3/16” The
small piece of ¼” rod cut from crankshaft end will be the Cylinder plug.
Cylinder Support
Cut a piece of the brass strip, 1 3/16” X ½”, file true.
Measure ½” from one end and ¼” from side, mark and punch.
Drill 1/8” hole for cylinder pivot.
With a file or hack saw, cut a grove from top to bottom on the face of the
cylinder support, just deep enough so that when cylinder tube is placed on it,
the cylinder will stay aligned while being soldered. This grove should run in
line with hole.
Cylinder Pivot Rod
Cut a piece of 1/8” brass rod, the same length as ballpoint pen spring. Drill a
1/16” hole in one end to hold spring and washer on, during assembly.
Cylinder retention spring washer
Big name for a little part, the #6/32 washer should be filed down to just bigger
than the diameter of the ballpoint pen spring and should slide over the cylinder
pivot rod.
Soldering Cylinder Assembly
One end of cylinder tube should be slightly pinched to retain cylinder Plug.
Flux both before placing plug into end of cylinder flush with the end.
Check fit of pivot rod (the end with out the hole) into hole of cylinder
support. If rod does not fit tight, punch edge of hole to move material in to
hole to tighten fit. Flux end of rod and inside of hole.
Place cylinder onto the grove of cylinder support after fluxing both faces, and
flush both ends. The hole in the support will be ½” from bottom of support, plug
in the cylinder should be at the top end of the support. A fine wire can be used
to hold cylinder to the cylinder support while soldering. The wire tie from a
loaf of bread or trash bag tie, works good, remove the paper from the wire
before using.
Make sure that pivot rod is 90% to cylinder support.
With all parts in place, heat and solder – plug into cylinder – pivot rod to
cylinder support – and cylinder to cylinder support, all at one time.
Be careful not to over heat or to run too much solder into cylinder when
soldering the plug in, this will bind the piston when assembling. Remove all
excess solder from face of cylinder support.
Drilling valve Hole in Cylinder
Assemble – upright, crankshaft, and piston. Turn the crankshaft so that the
crank pin is to its farthest point to the left or right side (90% horizontal) of
crankshaft center, and clamp in place. Cylinder assembly should be tilted as far
to one side as it will go, and lined up with one of the valve holes.
Now drill a 1/16” hole though the valve hole (that is lined up with the center
of cylinder) into cylinder. This will be the intake side.
When the crankshaft is rotated to other side, the hole in the cylinder should
line up with the other valve hole in the upright. If the holes do not line up,
determine which side of the upright exhaust hole needs to be enlarged to alien
the holes. Use a 1/16”drill bit and angle the hole in the upright, only. Do not
drill into cylinder. Use larger drill if necessary.
Intake valve tube
Enlarge the intake valve hole in the upright (on the same side of the upright
that the bushing is soldered on to) to 1/8”, but do not drill all the way
through, only enough recess to set 1/8” copper tube. If you drill all the way
through, all is not lost, the copper tube can be set all the way through,
soldered and filed off flush.
Copper intake tube needs to be soldered into the enlarged intake hole to
complete construction. The tube can be left strength or bent to turn out to the
side, or any other configuration that you desire. Make sure that it will clear
the flywheel and cylinder pivot rod with the spring and washer on it. This tube
comes very hard and will kink if bent without annealing first. To soften the
copper tubing, heat it very hot and then quench in water, this will make it very
flexible, but care should be taken not to bend it too sharp or it will still
kink. Leave a little extra near the end when bending and then cut to length.
Care should be taken not to be burnt when heating the tube, heat travels very
quickly though copper. If the end of tube, that is to be soldered into intake
hole becomes deformed, a round pointed object can be pushed into the end to
reshape it.
After shaping the intake tube flux and place end into enlarged intake hole in
the upright and secure or support. Care should be taken not to unsolder the
crankshaft bushing from the upright. I laid the upright on a firebrick, with the
end to be soldered hanging over the side and reinserted the ¼” aluminum tube
though the bushing and hole to keep it alien if it did come unsoldered. I laid a
piece of scrap steal between the intake and bushing to help absorb some of the
heat that will travel though the upright to the bushing.
Heat and solder the intake tube to the upright intake hole. If solder flows into
intake hole, use a 1/16” drill to clean out the tube.
Assemble and Run
Moment of truth – clean, lightly oil, and assemble all the parts. The spring for
the cylinder pivot rod and washer is held on by running a small wire though the
hole in the end of the pivot rod. Cylinder assembly must seat tight against the
upright to make a good seal. If they don’t seat properly, the pivot rod may be
at an angle. The pivot hole can be drilled to 9/64”. The little engine should
run on 5 to 8 lb. of pressure. If you have any problems, email me, or the club.
We will try and help.
Tips
Deburing – the edges of holes can be cleaned with a larger drill bit,
turn by hand. Straight edges should be cleaned with a file.
Vice- When holding things in the vice, I use the leather from an old boot
top to keep from scaring the finish on the metal parts or place between wood
blocks.
Magic Marker – can be used to mark the brass first and then do the lay
out with a sharp object. This makes it easier to see the lay out.
Layout –should be done very carefully and accurately as possible. Make
your marks with a sharp object that will make as fine of a line as possible, and
a ruler that has as fine of lines on it as possible. I also use a magnifying
glass to get as close as possible when laying out parts. Sloppy layout will ruin
a project quicker than any thing.
Soldering should be done with as low of a flame as possible. I didn’t
hardly discolor the part of this engine when soldering. It is best to heat the
part to be soldered from the opposite side than you apply the solder with a
flame no more than ¼” long. This will insure that the whole part is at the right
temperature. When the solder takes on the opposite side it will be drawn to the
other side by the heat of the torch. Put only as much solder on the part as it
takes for it to flow around to the flame. I use a small diameter electrical
solder as I can find. All that extra solder has to be removed, so there is no
need to put it on to start with.
Coleman Two, a ringbom
Stirling engine.
This is
the first engine I build all my myself. It is based on the first engine we
built, but with a new “tower” assembly. This tower is lighter, stronger, and
serves as a kind of heat sink, to help cool the top of the engine. The fan
blades are made out of “foam core”, to minimize damage if you get your fingers
in the way. Each fan blade can be individually adjusted for angle of attack.
The displacer is made of insulating foam. Some of these foam displacers have
failed on top of the stove, but the most recent one has worked for weeks without
a problem. The hole in the fan hub is a counter weight, which ensures that the
engine never comes to rest at Top Dead Center or Bottom Dead Center. This,
along with the spring which suspends the displacer in the middle of the
cylinder, allows the engine to start given only a slight disturbance, once it is
up to temperature.
 
The
resulting engine has a fairly clean design. Note the springs, which clamp the
plates to the glass displacer cylinder. This ensures uniform pressure while
also giving the glass a little room to move if it needs to. Note the grass
knurled knob at the top of the tower: this allows us to adjust the vertical
position of the displacer spring. In this particular configuration, the fan hub
is made of steel, and also serves as a fly wheel.
From
the top. Note how the tower “legs” fit precisely into slots milled in the block
at the top of the tower. This precise fit prevents the tower top from moving
under pressure.
 
The
engine from an angle.
Detail
of the engine from an angle. Note the small crank wheel, with multiple holes
for varying the crank throw; the adjustment mechanism for the vertical position
of the displacer spring; and the hand made displacer spring (we could not find
any commercial springs with the right characteristics).
Our
first “serious” Stirling engine is a “ringbom” engine. This kind of
Stirling engine differs from
most other configurations in that the displacer and the power piston are not
connected by a crankshaft. The resulting engine is a bit magical (how does the
displacer move if there is no crankshaft?!?) and noisy, but it can be self
starting and will run over a reasonable range of temperatures. For more info on
Stirling engines in general, check out
www.stirlingengine.com.
This is
the 2” graphite power piston and cylinder. The cylinder is just brass tube. The
graphite piston was bored out using a Forstner bit;.the cylinder was silver
soldered to the base.
 
This is
the displacer piston, also made of graphite. The metal sleeve is the cylinder in
which the piston rides. Ringboms have two pistons and cylinders, rather than
just one.
The
ringbom engine, in pieces. The glass displacer cylinder is in the middle of the
picture, with the displacer piston and the assembled engine top near the top of
the picture. The glass cylinder is a “globe” for a Coleman lantern.
 
The
assembled engine top, including the flywheel, power piston cylinder, displacer
cylinder, and displacer piston (in the background on the right, behind the top
of the engine).Note the scotch yoke used to connect the power piston to the
flywheel. This approach proved to have more friction than we could afford, and
we abandoned this approach after a while.
The
assembled engine. Note the displacer just visible inside the glass displacer
cylinder.
 
The top
of the engine with a new flywheel (on the far side of the picture). There is a
counter-weight attached to the flywheel. In the foreground you can see an
optical sensor (at the bottom) and a wheel with a pattern of lines on it. We
used the sensor and a computer program to compute the instantaneous angular
velocity of the flywheel. We then moved the counter-weight around until we made
the angular velocity as constant as possible (minimized the variations).
A
home-brewed fan which Ralph made. It actually pushes quite a lot of air, and
cools the top of the engine some 20-30 degrees F.
 
The
ringbom engine with the scotch yoke replaced, the fan attached, and a spring in
place to compensate for the weight of the displacer. The spring can be seen
above the displacer. It looks like a fishing pole, and is attached to the
aluminum blocks on top of the brass tower on the right side of the engine. Note
the two yellow temperature probes. Further note that we are now using a
commercial heater, rather than the tin can and light bulb. The displacer is made
out of aluminum, and is sealed with aluminum tape. The tape adhesive failed
after a while, as did the fishing rod spring.
The
same engine, at work. The fishing rod spring can be seen at the top of the brass
tower, on the right, with a small loop at its base. The horizontal brass wire is
used to center the string which attaches the spring to the displacer.
A
close-up of the spring assembly and guide. The numerous holes on the flywheel
allow us to set the engine up with a variety of different power piston throws.
A
fixture to allow infinitely adjustable power piston throws.
 
The
latest version of this engine, showing the displacer spring adjustment fixture.
Different springs alter the engine performance, as does adjusting the height of
the spring. Adjusting the rest position of the displacer effects the
temperature at which it starts to operate and the temperature at which it starts
to over-run.
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