DIY

How to Build A Sundial for the Garden

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KENNETH LIN
A. Measure and mark a 4 by 4 by 8 pressure-formed, treated post.

Build a sundial for your yard or garden, the ultimate in simple, practical technology for just a few dollars. (See the sundial illustrations in the image gallery.)

How to Build A Sundial for the Garden

Before there was the murderous regularity of a daily
schedule, before there was the clicking, buzzing, chiming,
and ticking of time, there was the sun and a shadow to mark
the passing of the day. A stake driven into the ground was
all the clock the Phoenicians, Egyptians, Etruscans and
other ancient civilizations ever needed … and while I’m
working in the garden on a July afternoon, it’s all the
clock I ever want.

The summer sundial is thus named because its accuracy is
limited to just that, the season which spans the warmest
months. But during that time it is remarkably accurate. It
works because the gnomon (the upright stick that casts the
shadow) is parallel to the earth’s axis and the sundial
face is parallel to the equator. If there were a real pole
standing straight up at the North Pole with a circle of
twenty-four hour numbers around it, the shadow of the pole
would mark the hours nicely. Since in all likelihood your
mailing address is a fair distance from the pole, you will
have to finagle the angle of your sundial a bit to get the
proper angle. More on that in a bit.

The Sundial Face

Begin the project by cutting a 20-inch diameter circle from
3/4-inch plywood. Give both sides two coats of primer.
While it is drying, start planning a design for the sun
dial face. You will choose colors, number style (Roman
numerals, standard, etc.), and some kind of illustration
you like. Draw some designs you like on a large piece of
paper. You’ll need a compass, straightedge, and protractor
to place the hours correctly. Each hour must be located on
a circle exactly 15 degrees from the next hour.

When you’ve decided on the design, use the paper as a
stencil and paint it onto the plywood circle and put on the
design numbers, hour lines, and illustration. For fine
detailed work like numbers, you might want to use paint
markers. They are better than permanent markers because the
paint from them does not fade quickly.

The Gnomon

The gnomon is a two- or three-inch length of threaded pipe,
one half-inch in diameter. It, like the flange, will rust
if not painted. The diameter of the gnomon should be a
little wider than the pipe’s, and you’ll need to improvise
a conical tip for it. The total length of the pipe and the
gnomon tip should not be more than three inches.

Preparing the Post

To make the sundial work correctly, it must be properly
mounted on a carefully prepared and placed post. Use a 4 by
4 by 8 pressure-formed, outdoor-treated post. Make sure it
is straight and free of large cracks. The 4 by 4 must have a
carefully measured and cut angle at the top, in order to
mount the sundial face correctly. To find the angle,
subtract your latitude from 90 degrees. For example, if
you’re making your sun dial in Columbus, Ohio, 40 degrees
N. latitude, you’ll draw a 50 degree angle on the 4 by 4.
Use a carpenter’s square to draw a line at right angles to
the 4 by 4, six inches from the top. That line becomes the
bottom side of the angle. Now you are ready to measure the
angle and cut it.

Use a protractor. Then cut it off as pictured. Ideally,
make the cut with a table saw for exactness, and check the
slanted face with a square.

Locate the center of the sloping face, and predrill the
center hole in the post. The 5/16-inch lag screw will
penetrate the post to a depth of about 1-1/4 inches. Drill
an additional hole in the center of the plywood sundial
face to let the lag screw pass through before going into
the post. Perform a trial attachment of the sundial face to
the post with the lag screw. This is to assure the screw
won’t crack the post, which is to be particularly avoided
when the post is set in concrete. If it fits well,
carefully remove the screw and the sundial face. Put them
both aside. Get ready to put the post in the ground.

Placing the Post

Obviously, you should choose a sunny spot for your post.
Don’t put the top of the post more than five feet above the
ground. If it’s higher, at times you will find yourself
looking into the sun and shading your eyes in order to read
the time. It’s best a little below eye level, but it can be
any height from eye level to fairly close to the ground.

Next dig a hole for the post. Be alert for any buried
cables or lines. No matter what height you’ve selected, the
slanted angle you cut must face north. Use a good magnetic
compass or, preferably, the North Star. Your post must be
perfectly vertical, and you can check this with a
carpenter’s bubble level.

Set the post in cement. When firmly set, which will be a
matter of several days, you’ll be ready to mount the
sundial face.

Attaching the Sundial Face

Attach the sundial face with the 5/16 by 2-inch lag screw.
Tighten the screw only to the point where you can still
rotate the sundial face with one hand and a little effort.
Next put the flange over the center of the sundial face,
with the lag-screw head showing in the center hole of the
flange. Screw the gnomon pipe into the flange with your
right hand as your hold the flange in place with your left
hand. Position the sundial’s face so that the 6 A.M. line
and the 6 P.M. line are horizontal. Next, align the gnomon
so that the 6 A.M. and 6 P.M. lines seem to go straight
through the middle of the gnomon. The 12 noon hour line
should also seem to go straight through the gnomon.

Setting the Time

Now set the time. Holding the flange in place with your
left hand, rotate the sundial face with your right hand
until the shadow of the gnomon on the sundial face reads
the same as the clock time (this must be done during
Daylight Saving Time). Mark the position of each of the
four flange screw holes. Remove the flange. Tighten the lag
screw firmly without moving the sundial face. Predrill
holes for the four screws that will attach the flange.
Attach the flange with the screws. Screw in the gnomon.

Gaining and Losing Time

As you watch the sundial throughout the summer, you may
notice that it gains a couple of minutes a week for a
while. Then it starts to lose time at about the same rate
for a while. This is mostly because as the earth
alternately slows down and then speeds up in its orbit, the
change is reflected in the sundial’s readings. Generally,
though, the time it gives will be close to clock time.

By late September, the summer sundial will have stopped
working for the year. It’s because the sun has gone below
the equator. The sundial face is a parallel to the equator,
so the sun is below the sundial face. That’s the definition
of fall. It begins when the sun moves below the equator.
Just like birds (and many of my friends), the sun goes
south for the winter.

The dial is a simple project, but every time I look at it
next to the garden fence and watch the world whirl along,
everything seems to make a little more sense.