How to Make a Pocket Sundial

Written by amber royer
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Sundials work by showing what time of day is represented by the shadow of the gnomon (the perpendicular piece of the sundial). Before you can make a functional design, you will need to know your latitude--and a bit of trigonometry. Different ways of making portable sundials were common in eras prior to the 17th century, when the pocket watch was invented. For instance, the shepherd's dial, or pillar dial, was a cylinder that looked something like a bank teller's capsule with a pointy stick on one end. But the most portable one was the tablet dial, which is the style you will complete in this project.

Skill level:
Moderate

Things you need

• Calculator
• Protractor
• Pencil
• 4-inch by 4-inch wood square
• Woodburner
• 1/4-inch thick wood scrap
• Mitre saw
• Fine sandpaper
• Foam paintbrushes
• Stain
• Sealant
• wood glue
• clamp

Instructions

1. 1

Starting at the noon mark, represented by a 1/4-inch vertical column in the centre of the wood square, use a pencil to mark hour lines that are accurate for your latitude by calculating the angle of each using the following formula: log tan D = log tan t + log sin theta; where D is the angle of the hour line, t is the number of hours away from noon times fifteen degrees, and theta is your latitude. Your finished chart should look something like this illustration but must reflect your own location.

2. 2

Carefully burn your pencil lines into the square by tracing over them with a woodburner.

3. 3

Use the protractor to draw a line on your wood scrap that matches the angle corresponding to your latitude. Use the mitre saw (or a similar tool) to cut along this line, creating a wedge, which will become your gnomon. The wedge does not have to be as long as the dial plate (the wood square).

4. 4

Sand down the edges of both pieces to remove any rough spots.

5. 5

With foam paintbrushes, stain and seal both the wedge and the wood square. Allow the pieces to dry.

6. 6

Glue the wedge onto the dial plate with the point of the wedge just touching the intersection of all the hour lines. Secure the wedge with a clamp and let dry overnight.

Tips and warnings

• If the mathematics involved make your head spin, use another resource (see Resources) that has a ready-made database that allows you to type in your latitude and print out approximated angles, which you can then trace onto your project . You can also buy or download free software that helps with sundial design.
• Use whatever materials appeal to you. Kids could make this out of cardboard and a soda straw. Or, for an even more durable sundial, etch your lines into metal and solder on a tumbled-stone gnomon.
• When in use, the gnomon must face directly south, casting its shadow toward the north, for the sundial to tell time accurately.
• Sundials, by their very nature, are not as accurate as pocket watches, so don't be surprised if you're not "on time." They also don't take into account daylight savings time.

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