How to Build A Sundial for the Garden

Build a sundial for the yard or garden, including making the sundial face, preparing and placing the sundial post, attaching the face and setting the sundial time.
By Sam Muller
February/March 1996
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B. Calculate the dial angle, cut and check with a square
KENNETH LIN
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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.


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