Build a Homemade Waterwheel

Because there was only about 4 inches of fall in the part of the
stream bordering our land, an overshot waterwheel was out of the
question. Unfortunately, I had little luck digging up
specific information on undershot wheels, so I had
to use common sense–and a by-guess-and-by-golly
approach–to make my project a success.

Early in the game I decided that an all wood wheel would be
too expensive and time-consuming to assemble. So,
considering the fact that an undershot design uses
paddles rather than the intricate buckets of an
overshot apparatus, I figured I’d search for a metal-spoked
waterwheel about 4 feet or 5 feet in diameter and simply fasten some
plywood paddles with 1foot-square blades to it.

I started by roughly calculating what I had to work with in
the way of water. The creek usually runs about 2 inches deep at
an 8 foot width. To create a weir that would direct the flow
toward the center of the stream (thus enhancing its depth
and velocity when at normal levels) but still withstand the
punishment of occasional deluges, I piled rocks in the
creek until the center channel was 16 inches wide and the
water–normally–was about 8 inches deep .. .
dimensions that I thought would be about right for the size
of wheel I had in mind.

Then, to get an idea of the water’s force within the
channel, I held a foot-wide board in that sluiceway and
used a small scale to determine the stream’s “push” on the
piece of wood . . . a force of about 7-1/2 pounds.

Next, I calculated the velocity of the water. I laid two
long poles across the creek, 10 feet apart, and floated several
sticks on the surface while I timed their progress. The
average figure–4 seconds to cover the 10 foot
distance–was then multiplied by 15 to arrive at 150 feet
per minute.

Now comes the fancy part: I’d found a 4
1/2 foot-diameter, 16-spoke metal wheel from an old hay rake
and figured out a way to mount a 12 inch by 12 inch paddle to the
rim at each spoke (I’ll tell you just how I did that later
in this article). To establish the estimated rotational
speed of the completed wheel, then, I just added the 27 inch
radius of its steel rim to the distance from that rim to
the 8 inch centerline of the water’s force on the
paddles, and came up with a lever arm of 35 inches.

The old formula C = 2?r gave me an overall
circumference of 220 inches, or 18.3 feet. Using the flow rate of 150
feet per minute through the weir channel, I
calculated–by dividing 150 by 18.3–that the
whole shebang would theoretically turn at about 8
revolutions per minute (RPM). Of course, knowing from
experience that theory tends to be more optimistic than
reality, I cut that estimate in half to account for
slippage and friction after the wheel and pump were
installed. (As it turned out, the wheel’s actual speed
averages just over 5 RPM!)

At this point I knew approximately how fast the wheel would
rotate, but I still had to deduce how much torque it would
provide in order to size my pump properly. A scaled-down
sketch of the side view showed that with one paddle dipping
8 inches into the water, the adjacent paddles would each be
submerged 4 inches, which would be equivalent to having two
paddles fully in the water at any given time, each
furnishing a 7-1/2 pound force from the current. By
multiplying the 35 inch lever arm by the 15 pound force from the
two paddles, I arrived at 525 inch-pounds–or about 44
foot-pounds–of torque available to power the pump.

Armed with the numbers I’d worked out, I could now decide
just how I was going to mount the wheel so it would
function under various flow conditions . . . and work out a
pump design that’d be compatible with the arrangement I
would finally settle on.

Getting the Right Frame in Mind

Since the normally shallow creek would get several feet
deep during a flood, I was a good bit concerned about
protecting my water pumper. Consequently, I
decided to set the wheel up on a frame so it’d swing with
the stronger currents . . . rather than holding fast and
trying to buck them.

To make the frame’s pilings, I took two 4 foot lengths of
1-1/4 inch galvanized pipe, slashcut one end of each, and then
threaded the remaining ends. Next, after capping the
threads, I drove one pointed stub down into the ground on
the creek bank and the other into the streambed itself so
that the pipes were in line with the weir channel and far
enough apart to accommodate the wheel and the swinging
carriage I had in mind.

That done, I removed the pipe caps and threaded a union to
the end of each pile, then fastened a short nipple and a
90 degree elbow to the post on the bank. I had about 12 feet of
1-1/4 inch pipe available to use for the cross-support, so I
threaded one end of that section into the elbow and held
the other end aloft–temporarily–on a tall
wooden X frame. After checking with a level to make sure
that the cross-pipe was horizontal, I used a plumb bob to
determine where to cut it so it’d line up with the vertical
post in the creek bed. Then I threaded that end, installed
another elbow, and joined the horizontal conduit to the bed
mount with a pipe of appropriate length. (I also clamped a
1/4 inch steel cable to the corner of this framework and
fastened its other end to an anchor driven into the bank
upstream . . . as extra insurance to prevent the force of
the water from buckling the structure.)

My next task was to build the swinging carriage that would
support the wheel and keep it in line. I started by welding
the two 6 foot lengths of 1/8 inch by 2 inch by 2 inch angle iron that would
hold the wheel perpendicularly to one side of a 5 foot
piece of 1/8 inch by 1 inch by 2 inch channel iron so that they were
centered, about 20 inches apart, and parallel to one another.
Next, I cut a 40 inch section of angle iron, scrounged up a
5/8 inch by 19 inch piece of steel rod, and used both those chunks
as braces between the channel and the angle iron.

Then–using the groove in the channel iron–I
hung the carriage from my 1-1/4 inch pipe framework and welded
a couple of 1/2 inch by 1 inch by 3 inch tabs to the channel opposite
each 6 foot parallel arm so that I could run 3/8 inch by 3 inch bolts
through the pieces to create a sort of hinge. (A U-bolt
later fastened to the pipe at each end of the carriage
hanger keeps the chassis from shifting sideways
when the wheel’s in operation.) And, to provide a place to
mount my pump–one that would also swing with the
carriage–I bolted a 1/4 inch by 8 inch by 8 inch plate to the angle
iron arm nearest the garden.

Waterwheel Wheeling and Dealing

The wheel was my next concern, and I tackled that problem
by first enlarging its center hole to 1-3/8 inch in diameter .
. . tapping the oiling orifice for 1/8 inch pipe and installing
a grease fitting . . .and drilling–then
threading–a 1/2 inch setscrew hole in the center of the
hub. A 1-3/8 inch by 30 inch cold-rolled shaft served as an axle,
and I decided to make my own bearings out of white oak
instead of purchasing conventional steel rollers . . .
which might seize after repeated floodings. To do this, I
bored a 1-7/16 inch hole through the cores of two 3 inch by 4 inch by 4 inch
blocks, and then drilled 5/16 inch mounting holes through the
shoulders, centered and perpendicular to the large bores.
After sawing both blocks in half–“splitting” the axle
holes in two–I cut grease channels and a feed into
each bearing. Next, I temporarily mounted the wheel and
axle assembly, within the bearings, to the 6 foot angle iron
swing arms . . . taking into account the necessary
clearance for the 12 inch paddles.

Since I knew I wanted the working ends of the paddles to
measure 12 inches by 12 inches, I extended their length to 2 feet to provide
enough surface area for a sturdy mount. I used a piece of
scrap 1/4 inch plywood to make my first 12 inch by 24 inch blade, which
I trimmed to the shape shown in the photos and then slotted
and drilled so it’d slip over the wheel rim and rest
against a spoke.

Once I was satisfied that the shape and mounting
arrangement would be satisfactory, I made up a sturdy
sheet-aluminum template and used it to mark out my 16
paddles on two slabs of 1/2 inch by 4 foot by 8 foot marine plywood. By
nailing four cutout blanks together, and drilling and
sawing holes and rim slots as a group, I found that I could
place those openings quite accurately. And after all the
blades were cut, I covered them with several coats of deck
paint for extra protection against the water.

To fasten the paddles to the rim, I used a pair of 1/4 inch by
1-3/8 inch U-bolts at each spoke, and to strengthen the wood at
the slotted part of the blades, I made up a total of 32
aluminum strips measuring 1/8 inch by 2 inch by 4-7/8 inch, which I
bolted over the slots in pairs with 3/16 inch by 1-1/4 inch brass
machine screws. (The sections of plywood removed when the
slots were cut were shortened, put back in, and used to
center the aluminum bridges.)

Different Strokes . . .

Now that the wheel and framing were completed, I felt I’d
really accomplished something . . . but I still had to
figure out –and construct–a pump
that’d work with my setup. To keep things simple, I set my
sights on a single-acting pump (which creates suction and
pressure on one side of the piston only) so I wouldn’t have
to provide a packing gland for the piston rod. At the same
time, I figured I’d mount its cylinder on a swivel, thus
eliminating the need for a connecting rod and guides.

But the question of how much displacement I could have
still remained. I knew the length of the pump mechanism
would be limited to 42 inches (the distance from the wheel’s axle
center to the upper frame member). So I finally settled on
a 9 inch throw for my crank, which meant that my piston would
travel 18 inches . . . and that the two parts together would take
up 27 inches overall. This would leave 15 inches for the pump fittings
and swivel bracket, a working space I could easily live
with.

Choosing the cylinder bore proved to be a compromise
between what I wanted and what was available in standard
hardware. A quick wheel-force diagram showed me that the
15-pound force acting on my paddles at 35 inches from the
centerline on the shaft–and then transferred
through a 9 inch crank–would amount to 35 divided by 9
(or 3.88), multiplied by 15 . . . a healthy 58.3 pounds of
force.

Dividing this number by the area of the piston (I decided
on a 2 inch Schedule 40 PVC pipe cylinder, so its
cross-sectional area–using good ol’ ?r ²
–was 3.14 square inches) gave me the available
pressure of the pump (18.6 pounds per square inch). From
there, since I knew that it took 0.43 psi to raise water
one foot in height, I could calculate the total head the
pump would deliver (43.25 feet . . . plenty for my
purposes) by simple division.

Furthermore, with all my “unknowns” known, it was easy for
me to calculate that, guessing my wheel speed at 4 RPM, the
2 inch by 18 inch pipe pump could deliver roughly 13,565 cubic
inches, or 58 gallons, per hour . . . which would amount to
almost 1,400 gallons a day!

Acquiring the pump’s components was simply a matter of
going to the local hardware and plumbing supply store and
picking out the parts I needed. My cylinder was just an 18 inch
length of 2 inch Schedule 40 PVC pipe, equipped at one end with
a 2 inch slip-to-pipe female adapter and at the other with the
same type of fitting terminated in a male thread. I screwed
the latter end into the common of a 2 inch galvanized T, then
bushed the T’s other two ends down to 1/2 inch. On the intake
end, I used a short nipple to a 1/2 inch swing check valve.
Then I concentrated on creating the piston parts.

The piston rod, a 5/8 inch by 26 inch stainless steel shaft,
required a bit of machine work, since it had to be threaded
at each end. One tip just needed a 5/8-11 thread 1-3/4 inches
long, but the other had to be cut down to a 1/2 inch diameter
for a distance of 1 inch. A 5/8 inch-long 1/2-13 thread was added
to this stub . . . which left a 3/8 inch length of
smooth surface between the threads and the step to
the rod’s 5/8 inch diameter.

With this done, I drilled a 21/32 inch hole directly in the
center of a 2 inch galvanized pipe plug, then slipped the
piston rod through that opening so its 1/2 inch end was on the
same side as the pipe threads. A couple of body
washers–with 1/2 inch center bores and 15/8 inch outside
diameters–made excellent buttresses after I curved
their edges slightly with a file and sandwiched two
2 inch-diameter leather piston cups between them. A 1/2 inch nut
and a cotter pin held this homemade piston in place on the
end of the shaft, and to alleviate the effects of water on
the leather, I soaked the parts in neat’s-foot oil before
slipping the piston in place and threading the pipe plug to
the cylinder’s plastic adapter. (The leather plunger will
slide home much more easily if you carefully taper the end
of the cylinder’s bore with a file.)

The connector at the opposite end of the piston rod was
just a 1 inch by 1 inch by 3 inch block of steel drilled and tapped 1 inch
deep at one end to match the rod, and cross-drilled at its
other end to a 17/32 inch diameter. The wheel crank–a
3/8 inch by 2 inch by 11 inch piece of flat steel–was drilled out
on a 9 inch center to join the 1-3/8 inch axle and the connector,
and I welded a 1-9/16 inch length of 1-1/4 inch pipe to the
large-holed end, and a 3/4 inch piece of 1 inch-diameter
cold-rolled rod (tapped for 1/2-13 thread) to the other, to
serve as crank collars.

Once I’d fabricated those metal parts, I constructed the
swivel bracket that would hold the pump in place. That
involved trimming out a 6 inch by 8 inch piece of 1/8 inch steel plate,
welding two 1/4 inch by 3 inch by 3 inch by 3 inch angle iron sections to one
end of this platform so that the lips were aligned with the
plate’s sides, and drilling a 1/2 inch hole 1 inch from the end of
the plate at the butt joint of the two angles.

To mount the pump to the bracket, I drilled a 7/8 inch hole
that was centered and 2 inches from the baseplate through each of
the upright angle iron lips and let the 1/2 inch pipe nipples
on the T serve as fastening pins. I then pinioned the
swivel bracket to the 8 inch by 8 inch mounting plate on the wheel
carriage, using a 1/2 inch by 1-1/2 inch bolt, two nuts, and a
cotter pin.

Having come this far, I breathed easy: The rest was just a
matter of fitting and fine-tuning. To check the wheel’s
lateral play, I cut a section of 1-1/4 inch Schedule 40 pipe
into three lengths (3 inches, 4-11/32 inches, and 4-19/32 inches), and used
two as spacers between the wheel hub and the
bearing blocks and the third as a keeper collar on the end
of the shaft opposite the pump. Also, I placed 21/4 inches
outside diameter flat thrust washers between the pipes and
the wooden parts, tightened the hub’s 1/2 inch setscrew, and
locked the collars to the main shaft with 3/8 inch by 2 inch machine
bolts.

Then I fit the crank to its end of the shaft (securing it
by–once more–using the technique of tightening
a bolt run through a hole drilled in the axle) and fastened
its other end to the piston-rod connector with a 1/2 inch by 3 inch
bolt and a lock nut. (I’ll tell you now, if you try a
similar project yourself, be sure to employ some form of
locking mechanism–whether it’s cotter pins or a
thread seal ant–on all your fasteners, or you’ll be
re-tightening them on a regular basis!)

Before I set the wheel into the water, I had to finish up
the plumbing. On the suction side, I just ran a 6 foot length
of heavy-walled plastic hose that terminated at an adapter
and a 3/4 inch foot valve submerged in the water. To protect
the pump from foreign matter, I wrapped the intake with
aluminum screening . . . and later made up a
gravity-operated sand trap–from some 2 inch Schedule 40
PVC pipe, a T, a 90 degree elbow, and a bit of woven filter
packing–which I placed in line between the foot valve
and the pump to catch and settle out the debris.

On the pressure side (the one with the swing check valve),
I installed a 1/2 inch nipple and T to the check and threaded a
small pressure gauge into one of the T’s ports. I then ran
my supply hose to the garden area and terminated it in a
garden-hose fitting and another T . . . which I plan to put
to use later on when I can get around to installing a
pressurized holding tank and a small, decorative fountain.

Finally, I filled the wheel hub with grease to keep it from
rusting to the shaft, ran plastic oil lines to the oaken
bearings, and let the machine down into the water.

Success at Last

You’ve probably guessed that my waterwheel performed just
as I expected it to. But it really surprised me the first
time the water level in the stream increased to a foot or
so. Then the wheel turned at a very respectable 11 RPM and
could have delivered 3,875 gallons of H₂0 to my garden in
the course of a day. The only real problem I’ve experienced
with my highly competent water pusher is the occasional
“logjamming” that occurs when debris is carried downstream
in high waters, and I solved the worst of that easily
enough by driving lengths of closely spaced pipe into the
creek bed upstream of the machinery.

So after waiting 65 years, I finally built a useful version
of my great-grandpa McDowell’s toy waterwheel. With a total
investment of about $250 in the project and a lush crop of
vegetables as a result, I can’t complain about the many
(enjoyable) hours of spare time it took me to bring my
childhood fancy to reality.