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| Ten Cylinder "Elbow
Engine" |
USA - Manufacture date:
2007
Bore = 1/4", Stroke 1 1/8", Flywheel diameter
= 3 1/2"
Style: Multi Cylinder, Single Acting, Hobson's Coupling |
Dimensions: 71/2" length x 6" width x 5
1/2"
height
(includes
wooden base) |
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The Completed Elbow Engine |
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This little engine's basic design has
been a personal favorite for years.
I once had the opportunity to repair
one for a collector and I've been
in search of my own ever since. They
seldom show up on Ebay and hardly ever
leave a collection, so the only alternative
is to build one. It is known
as an Elbow Engine and is based on a
mechanism known as a Hobson's Coupling.
It is used to transfer rotation across
90 degrees via a mechanical coupling.
The action produced in the process
is known as "simple harmonic motion".
I just call it hypnotic and fun
to watch. The design you see here is
a "10 cylinder version, requiring
only 7 moving parts to operate. You
read that correctly... a 10 cylinder
engine with only 7 moving parts. A 6
cylinder version is much more common
and uses only 5 moving parts. |
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After years of lamenting my lack of machining knowledge
and skills, I finally acquired
a small lathe and a small
milling machine and
began teaching myself to
work metals. The exciting
part of this engine, at
least for me, is that
it is my very first engine
building project. A few
weeks before these photos
were taken, this engines
was only a small stack of scrap
aluminum,
steel and bronze bar stock,
which I was finally able to turn
into a working engine. I'm
just a little bit chuffed
about that...LOL. The basic
engine design was published
by Popular Mechanics, sometime
in the 1960's and quite
a few engine builder have
taken up its deceptive challenge.
I was brilliantly ignorant
enough to toss out the plans
and choose to go with the
design in my head. Thusly,
the saga begins. ....LOL |
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There were a number of considerations that
went into deciding to build this engine,
and to build it "my way".
The first was the desire for something
one of a kind that would fit nicely
into this collection. The second was
to make it a challenging project and
the third was to try out a couple of
ideas that had been fermenting in my
head for a long time. The appearance
I finally decided to shoot for was something
close to a Victorian style preferably
something that would look at home on
a gentleman's desk or residing
in his library. This lead to the idea
of using bronze accents and gun blued
steel for various components of the
engine. This was modeled out in 3D and proved to work well together
within the overall idea. |
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3D Proof of Theory Rendering |
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This project began with more than enough challenge for
any novice engine builder. I decided
to make a classic flywheel with 10 spokes,
rather than use the normal flat hub
style with a few holes drilled in it.
Having fitted my lathe with an indexing
plate, drilling evenly spaced holes
in a radial pattern was not a huge undertaking.
This part of the job went quickly, as
did turning the tapered and shaped
spokes from 1/4 inch hot rolled steel
rod. Things got a bit more interesting
when it came time to assemble all the
parts. How exactly does one install 10
individual spokes into 2 separate
rims and make them run true?
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It was a puzzle that took a or two day to sort out, but the answer woke me from
a sound sleep at about 4:00 in the
morning. I got up and went to the shop
where I placed the outer bronze
rim on
the lathe's chuck and then put the center
hub on a piece of 1/4 inch drill rod
and chucked it in the tailstock. When
the two rows of holes were aligned,
and measured with a dial
test indicator, the hubs were obviously
concentric. Ahhhh.... the smell of success
is sweet.
By carefully inserting
opposing spokes and hand turning the
lathe chuck to check things, as I went along, the rim
and the hub remained concentric and
held their position quite nicely as I used
red loctite to secure them in place.
A press fitted outer rim completed
the flywheel by locking the spokes in
place and hiding the exposed holes in
what was now the interior rim of the
flywheel. A quick spin test on the lathe
proved the flywheel was concentric and
ran true, with no wobble. Beginner's
luck?... maybe, but the idea worked
out well and the project progressed another step.
Building the flywheel was surprisingly
easy and is something
I'll be willing to tackle again in future
engine projects. I did mention that
this little engine has hooked me
on building my own... I didn't? A
few dollars worth of scrap metal and
a few enjoyable hours of work beats
paying the rediculously high prices that
handmade engines have
risen to, by a very long shot. |
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The
Finished Flywheel Installed
on Drum
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The
Revolving Drums and Bearing
Plates
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The next step in the journey was to make the pistons.
The engine uses 5 piston sets bent
to 90°. Each end of a set acts as
the piston in one of the cylinders of
one of the revolving drums. Each set
acts in unison as air is applied or
exhausted to extend or retract the pistons.
This action causes the drums to turn
in unison and run the engine. The piston
sets have to be perfectly set at 90°
or they lock in the cylinders and nothing
will turn freely. This process took
several attempts before things were completely
squared and turning "relatively free"
within the 10 cylinders.
One also has
to take care that the pistons are
made to the proper length or they will
strike
the bearing plates and stop the motor.
By adding the decorative spheres, I
had managed to make things even harder,
since I now had to avoid having them strike
the top of the drums too. Some experimentation
ensued and the proper middle ground
was soon achieved by a bit of easy math and
some trial and error testing. There
is very little margin for error in any
Elbow engine, but this one has next
to no wiggle room at all. A slight misalignment
is all it takes to stop the motor dead
in its tracks. |
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Test
Fitting the Pistons
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My training as a real world artist and experience in the world of 3D design
has taught me that sculpture must be
interesting from any angle from which
it is viewed. You can't ask the viewer
to stand in one place, just so you can
hide your errors or lack of imagination.
Any viewing angle without some point
of interest
means your design has missed the mark.
The whole engine needed to be interesting
and it took a bit of work to come up
with a workable design that had the
right sort of total visual impact while retaining
the intended style..
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Rear
Structure
and Partial
Air Line
Test Fit
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The original plans for an Elbow engine used a rather plain looking piece of aluminum
plate as a rear support
for this engine. To
achieve the Victorian
look that I hoped to
have when finished,
something a bit more
visually complex would
have to be created.
A number of ideas
were modeled in 3D until
a pair of classic columns were chosen. They worked well
with the spoked flywheel
and a flying bridge
soon followed them into
the design. This meant
the supply and exhaust lines
could no longer be hidden
within the engine base
itself. Exposed
lines were anticipated,
but their final design would
wait until the main
structure was in place
and fairly close to
properly adjusted.
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Air
Lines Installed for
Test Run
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As things progressed, the need for fitting the air lines grew. The drums needed
to be adjusted to their
final positions and
the engine was nearing
a place where it could
be test run, but not
without an air supply.
The bronze plumbing "T"
design was chosen
for appearance as were
the flanged fittings.
These were turned on
the lathe in three pieces
and soldered together.
The spherical section
was drilled for a slip
fit, making it adjustable.
Once the proper location
was found, the pipe
was drilled using the
T fitting as a drill
guide. The pipe was
then locked in position
with red loctite, in
order to avoid
having to solder the
anodized steel pipe
surfaces. Red loctite
is an excellent substitute,
in certain instances,
where soldering is not
possible or is considered
undesirable. It forms
quite a strong joint
and acts as an airtight
seal to prevent leaks.
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One
would
think
the
hard
part
of the
project
was
behind.
The
machining
work
is all
done,
much
of the
heavy
polishing
is complete
and
all
that
remains
is the
test
run.
Nope...
it ain’t
that easy
there
Sparky...(grin).
These
little
fellows
are
very
finicky
in their
simplest
form.
This
one
was
even
more
so with
its
additional
cylinders
and
somewhat
altered
stance.
No...
this
is where
things
got
difficult
and
rather
frustrating.
Proper
alignment
is actually
difficult
to achieve
and
the
sweet
spot
is quite
elusive.
Until
everything
is exactly where
it needs
to be,
friction
is the
enemy
and
binding
in the
extended
pistons
is the
norm.
Consider
that
each
time
the
engine
has
to be
disassembled,
it also
has
to be
readjusted
and
you
can
soon begin
to quietly
"converse"
with
yourself
as you
work. |
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This engine has been apart uncounted times, the pistons
were
tried
in combination
after
combination
until
finally
an undetected
problem
was
spotted.
Using
Play-Doh
to make
an impression
for
comparing
the
pistons
revealed
a slight,
but
identical
deviation
in the
bend
of each
one.
This
tiny
problem
was
causing
a .020
inch
mismatch
when
all
the
pistons
weren't
"facing
the
same
way".
Once
matched
in proper
fashion,
the
friction
problem
was
soon
conquered.
Ok...
time
to test
run
it again... sort
of .
My air
compressor
is of
the
small
bench
top
5 gallon
variety
and
does
well
to keep
up with
a large
bore
steam
engine,
having a
sealed
system.
An Elbow
engine
is anything
but
a sealed
system,
so the
poor
compressor
can't
keep
up with
the
demand.
The
engine
will
only
run
for
a few
revolutions
before
the
compressor
runs
out
of air,
but
at least
it runs.
Excitement
enough
for
a first
build
,but
a fair disappointment
in that
I can't
easily
play
with
it.
Sadly,
that
fun
will
have
to await
the
arrival
of a
larger
air
compressor,
hopefully
really
soon...LOL
The
engine
was
finished
up with
a detailed hand
polishing
and
the
addition
of a
hand
rubbed
wooden
plinth.
I'll
offer
a couple
of tips
for
those
looking
to build
this
engine.
It is
a deceptive
build.
The
machining
part
is pretty
straight
forward
and
well
within
the
abilities
of most
intermediate
level
machinists.
That
is where
the
deception
begins.
You'll
need
the
patience
of a
biblical
Job
and
stubborn
perseverance
bordering
on obsession,
when
it comes
time
to adjust
and
test
the
little
dickens.
This
is not
the
perfect
choice
for
a first
build
engine
project
and
modifying
it,
as I
did,
certainly
tested
my rather
limited
experience
levels
to the
maximum.
I got
through
it with
some serious
head
scratching
and a
lot
of encourqagement
from
the
crew
over
at the
Home
Model
Engine
Machinist
Forum.
I learned
a tremendous
number
of new
tricks,
but
sometimes
failure
was
feeling
uncomfortably
near.
All in all, I'm pleased with the outcome and I've totally
enjoyed
making
the
discovery
that
I too
can
successfully
build
my own
engines.
You
can
bank
on there
being
more
to come. |
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