# Pocket Sundial

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## Introduction: Pocket Sundial

Ok, that is probably not the most likely of scenarios, but a pocket sundial can actually be a fun and useful thing to have. It can tell time fairly accurately while the sun is out, and a built-in compass can be useful at any time.

This Instructable will document my experience making one for my self, and show you how to make one of your own. So, lets get started.

## Step 1: Tools and Materials

Here are the necessary tools and materials for this project...

TOOLS:
- Hacksaw (and/or band saw)
- Compass (for making circles)
- Scissors
- Sandpaper (several grades between 60 and 400)
- Dremel rotary tool

MATERIALS:
- 2 X 4 (I am using pine)
- Small compass (for finding North)
- Small piece of plastic (about 3" x 3")

SAFETY EQUIPMENT:
- Shop goggles
- Gloves

## Step 2: Math Time

The main feature of the sundial face is, of course, the lines that will eventually be used to indicate the time. It is important that these lines are at correct angles to insure that your sundial will be accurate. The equation to determine the angle of each "time line" (Ø) is this:

Ø = Tan-1(Tan(t)*Sin(L))

Where:   t = the angle from 12 on a normal clock [ t(noon) = 0°, t(1:00) = 15°, t(2:00) = 30° , t(11:00) = 15° , etc.]
L = the geographical latitude where you are, or where you intend to use the sundial

This will need to be done for every line you intend to put on your sundial. But dont worry, Excel is here to save the day! Above, you can see a screen shot of my spreadsheet with the equations used in each column.
Your lines can be at every hour, every half hour, or every 15 min (any more than that is probably beyond the precision of the sundial, and not worth the extra time and math). Mine are every 15 minutes from 4am to 8pm.

Your latitude will also be important in making the gnomon (the piece that stands vertically and casts the shadow on the sundial's face). The top edge of the gnomon will be the part of the shadow which will line up with the time lines. The angle between this edge and the face of the sundial must be equal to your latitude. Other than that, the gnomon can be as simple as a right triangle, or a complicated as you want.

In addition to your latitude, an other value you will need to know is the magnetic declination of your location. A compass points towards "magnetic north", but for an accurate sundial, you will need to know which direction "true north" is. Again, this will depend on where you are on the earth, and can be determined using the map above, if you are in the continental US. Sorry, to everyone else. However, I am sure that similar maps can be found for other regions of the globe.

## Step 4: Test Your Design

Once you are satisfied with your design test it out to make sure it works as expected. To test it, print out the face design and glue it to a note card. Then cut out a right triangle gnomon, glue it to a piece of note card and tape it to the face. Find a safe place that will receive direct sunlight for a significant portion of the day (like a windowsill). Position the sundial so that the gnomon points toward true north. Observe the dial for at least one full day, checking how accurate the sundial is (compared to a clock that you know is correct). Keep in mind that the sundial will not change with daylight savings, so it will appear to be one hour behind while daylight savings time is in affect (be sure to remember this when actually using it as well).

The sundial might be a bit off, but that does not mean there is something wrong with the design. If the dial seems to be off by the same amount at all times through out the day, that probably means that it is not actually pointed toward true north (which is likely since the magnetic declination was a bit of an estimation). If this is the case, rotate the dial until it is correct and then observe for another day to be sure that it is consistent and accurate. If it seems to be right some times in the day, and way off during others, there is probably a problem with the angles.

## Step 5: Start Building

Finally we get to build it!

Cut a 4 inch segment from your 2x4 using a hacksaw (or a band saw if you have one). Then, using your compass, draw a circle that is a bit bigger than the overall size of your design (to allow for sanding and small accidents). Do the same on the other side of the wood. Cut off the corners and edges up to the sides of your circles to get it closer to the right shape ans size.

Then, using a dremel (or other rotary tool) with a round sanding attachment to sand the piece even closer the right shape/size. This step should be able to get you to a roughly circular puck. I also decided to round the top and bottom edges a bit.

Next, sand the puck using sandpaper, moving up from 60 grit to around 220 grit. Use the 60 to help shape the puck more to the desired size/shape, and use the rest to smooth it out. After doing this I decided to make the top more rounded than the bottom so that I can easily tell them apart. To do this, I used my compass to draw a smaller circle on the top (first pick which side will be to top), to be used as a guide. Then, using the dremel and the sanding attachment bevel, and then round, the edge up to the guide circle. Sand again by hand to get it smooth.

## Step 6: Cut It in Half

This sundial will be a two-piece -- the bottom will have the actual dial, and the top will be a cover -- so the next step is to cut that puck in half. To do that, first draw a line around the outside of the piece by putting a pencil on top of a sturdy object next to the puck, and turn the puck all the way around to create a line that goes all the way around the puck, at a constant height. I used a glass coaster to put my pencil on because it happened to give me the desired height, but a good trick is to use a deck of cards (with out the box) so that cards can be added or removed to get the exact height you need.

Then, carefully cut the puck in half, making sure to stay on the line. Again, a hacksaw will work fine (that is what i used) but a band saw will have the advantage of making a cleaner, straighter cut, quicker and with less work.

Once it is cut, sand the new surfaces flat and smooth on each half.

## Step 7: Shaping the Bottom

Now that we have two halves, we will need to shape them so that they fit together nicely.

First is the bottom half. We need to cut a groove around the outer edge. Using a compass, draw a circle that is about 0.5 cm from the outer edge. Then use the deck of cards trick to draw a line around the outside to mark the desired depth of the groove (again about 0.5 cm from the top edge). The use a routing attachment and a routing bit with the dremel to cut the groove all the way around the piece. Be sure that the bit depth is matched up with the second line (around the outside surface). Use the routing setup to get close to the circle on top, starting from the out side working inward carefully. Then use the sanding attachment to finish it up and get it the right shape.

Next you will need to cut out a hole for the compass to fit into. Print out your design, and cut it out to use as a template to help you put the hole in the right place. Trace around the template or the actual compass, and use this circle as a guide when cutting the hole. Get out the router attachment and bit again and set the bit depth to match the height of the compass. Use the router bit to get the right depth and get close to the circle you drew, then use the  sanding attachment to finish it up and make it nice and clean

## Step 8: Shaping the Top

Next, you will need to shape the top half so that the two halves will fit together.
To do this, first put the two halves together, making sure that they are aligned correctly, and use a pencil to trace around the raise circular area of the bottom piece. This will make a nice out line to follow when cutting out a hole in the top piece. Next, using the routing setup on the dremel, with the bit set slightly longer than before, start in the center of the top piece and begin removing material. Do not go all the way to your line just yet.

Then, use the sanding attachment and the sandpaper to clean it up and get closer to the line. Be sure to check its fit with the bottom half frequently. You want it to fit snugly but still be easy to pull apart.

Once you have two halves that fit together well, you can sand the out side surfaces with the two together, to make them match up even better

## Step 9: The Gnomon

My method for making and attaching the gnomon is to design it to have two small pegs that will line up with slots in the dial face to keep it in place and properly aligned. With this method it is also possible, and easy, so make several gnomon that can be used interchangeably for either a different look or incase one breaks

The gnomon can be made from just about any sturdy material, however many metals will screw up the compass reading and should not be used in any part of the sundial. I used a stiff piece of plastic (polypropylene actually) that I cut from the lid to a large plastic jar. Whatever material you use, make sure that it will not break or bend too easily, and be sure that it is flat. Print the design and tape it to the piece of material (I like to use double sided tape), and the cut the shape out of the material. Be very sure that the "latitude corner" is at the right angle, and be sure you know which corner it is.

To make the slots, I used the tool that comes with the dremel for opening and closing the collet. The end of the tool with the flat head is just the right size and shape tor create the slots. Before making the slots, be sure to draw a vertical line along where the noon line will be, and mark where the two slots should go (from the point where all the time lines meet, up to where the time lines are visible in your design). It is a good idea to use a print out of you design as a guide. Then, use a hammer to pound this end of the tool into the face a bit. Check with your gnomon to see if it is deep enough. If its not, keep pounding it in a small amount at a time until the gnomon sits flush and the pegs cannot be seen. At this point, check again that the angle is correct (sanding can fix it if it is a little off). It is a good idea to test this method on a scrap piece of wood first.

## Step 10: Making the Face

The last thing to do is to put the time lines and numbers onto your sundial. Before beginning this step, be sure that the surface is sanded smooth the way you want it.

Now, you will need to trace the design in pencil and then test your sundial with the pencil lines to make sure it works before making anything permanent. Place it in a safe sunny place like before. After a day of observation, if everything seems to be working as it should, you can now transfer the design to the wooden face. You can also leave a pencil mark next to the compass to indicate where the compass arrow should point for an accurate reading.

There are several ways to get your design onto the face of our sundial. You can carve it in, paint it on, or burn it into the wood.

Remember, no matter which method you choose, its always a good idea to test it out on a piece of scrap wood so make sure it will look the way you want it to.

## Step 11: Finishing Touches

At this point you have a working sundial, but there are a few more things that can be done that will make it look nicer, last longer, and make it easier to use.

First, you can apply a finish to the wood to make it look nice and protect it from damage. Again be sure to test your finish on a scrap piece to make sure it will look how you want it to. Also, make sure the compass and gnomon are removed first. You can also paint or carve some designs onto the outside of the two halves.

Once you have the wood the way you want it, you should glue down the compass in its hole. You can use superglue, a hot glue gun, or some epoxy.

Another useful addition is to add an elastic strap to the inside of the top half to secure the gnomon when not in use. Also, if the two halves fit a little loose, an elastic band or small pouch can be used to hold them together better.

## Step 12: Use It!

The sundial is now finished. The only thing left to do is use it.

To use your new sundial, take off the top half, remove the gnomon and put it in place on the dial. Make sure that the sundial is in direct sunlight, and either hold it level or place it on a level surface (this is important and will affect the accuracy of the sundial). The compass might have a small air bubble (mine does), which can make it pretty easy to see if it is level (the bubble should be in the center of the compass. Aim the gnomon toward true north and take a reading to find out what time it is (dont forget to adjust for daylight savings time if necessary).

Runner Up in the
Summer Camping Challenge

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## Questions

Am I a little too simplistic? It seems to me that all you need is a compass. Once you know which way north is, just looking at your own shadow can give you a good estimate of what time it is. I have done this all my life and have been fairly close.

Still a very nice little tool to have. Great job!

something to aspire to

Thanks! This is not "your grandfather's pocket-watch"! hahahah Now what I wonder is how to comfortably hook-up a band on it, so its a wrist-"watch". hahahah

Really great instructable. Thanks for the details.

Awesome Instructable!

I wanted to design something along these lines a long time ago but never got around to it: now I'll make myself do it! Thanks for the 'ible! :D

This is the coolest thing I have seen in awhile! Great job!!

A really nice piece of work.

Nice sundial! These have always fascinated me, and it's nice to see someone come up with something portable and practical :)

Just a note on judging time in the outdoors, especially if you're deciding on when to set up camp...use the hand span method to estimate how much daylight you have left. To do it, hold your hand at full arm's length, palm in and thumb up, fingers together. "Rest" the lower edge of the sun on your index (pointer) finger, and "walk" your hands down to the Western horizon or mountains. Each span is about an hour, so each finger width is around 15 minutes.

Nice work!

How do yo adjust the time regarding the season and latitude?

7 replies

Hey, thanks.

As far as I am aware, the only seasonal adjustment that is necessary is for daylight savings time (where applicable). The sundial will always read your local standard time (it will say noon when the sun is directly overhead), so when daylight savings is in affect, you will have to compensate by adding an hour to whatever your sundial says.

Using the sundial in different latitudes is more complicated because the value of your latitude is used in the equations for drawing the time lines and in making the gnomon. Technically a new gnomon and dial face would be needed. However, with a sundial this small, the precision is already low enough that if you are with in 10 or 20 degrees of latitude it should not affect the accuracy a whole lot. However, since it is so easy to remove the gnomon, it might not be a bad idea to make a new one to match the new latitude, which will help decrease the margin of error.

To be little bit more precise, the sundial will read local solar time. Your local standard time may be up to around half an hour off from that, depending on where you are within the time zone. You can compensate for this in your calculations, but then the sundial will only be usable at your own longitude.

Ah yes, good catch. Thank you for the clarification.

Longitude incides directly, but latitude a bit less. Anyway, you must consider it, I think.

Actually, there is a way to use a sundial in a different latitude--you just tilt the sundial by the difference in latitudes.  A couple of ways to do that.  The most general might be a leg that comes out on one side, calibrated in latitude angles.  Another way might be to cut some five degree wedges, and then you can stack them.

Changing out the gnomon isn't good enough, because the formula for the angles depends on the latitude.

By the way, probably an easier way to generate the face for this wooden sundial without measuring small angles is to use the automatic generator in my papercraft sundial ible to make a pdf file, then load the pdf file into Inkscape, shrink it down, and then transfer the angles to the wood with pins.  This would also compensate for longitude (if you don't want that, set the longitude to the nominal central longitude of the time zone).

Good idea, I had not thought that. Maybe a movil (articulate) gnome too, it could help.

OK, now I understand, thanks!

Great idea. You wouldn't need the compass if you know that the sun rises in the East and sets in the West, but it does increase accuracy (depending on magnetic declination) and ease-of-use.