I saw a kit at Paxton Gate on Valencia in San Francisco on how to make a diptych sundial and was going to get it for my friend Ben, but then thought of all the extra wood I had from previous projects and decided to just make one from scratch. While I was once upon a time a physicist, I didn't really feel like figuring out all the mathematical details, luckily there are some pretty useful websites dedicated to sundials of various types.

I used this one as a model: http://www.mysundial.ca/tsp/diptych_sundial.html

But this one is also a nice site: http://www.sundials.co.uk/projects.htm

Step 1: Tools and Materials

For the Basic body:
- 2 Wood blocks of equal size
I had a bunch of black walnut left over from making my side table with inset greenhouse, so that's what I used for this project. I cut two square pieces and squared them off (more of less) so that they fit flat together. I used japanese-style hand saw which was probably not the easiest choice (easiest would probably be a band saw, but then of course you need to have a band saw...) and required a lot of sanding to get it flat. Note : It doesn't matter if the blocks are the same thickness, only the same dimensions on the face. You just have to make sure that the base is deep enough to inset your compass.

- Compass
I looked at using small compasses or a large compass and decided to go with a small one, but I think either could be cool.

- Small nails/tacks

- Thin string

- Dremel or router

- Wood carving tools

- Sandpaper and sanding block

For the hinges:
- Aluminum flashing
If you want to be more fancy/polished, you could use silver, and then you could solder the hinges so they look a little nicer, but aluminum flashing is cheap and readily available at any hardware store.

- Jewelers saw and V-block
A V-block makes it easiest to cut out the hinges using your jewelers saw. If you have a laser cutter, then these tools would not be necessary and the results would probably look a bit cleaner, but once you get used to cutting with a jewelers saw, you'll find you can make these shapes pretty easily and quickly.

- Needle Files

- Small nails

- Pin Vise
A pin vise is used for drilling very small holes. This would be the easiest way to make the holes for the small nails that will hold the hinges to the blocks.

For the decorating :
- Paint (latex or oil-based)
Acrylic could work too, but just be aware that if you use acrylic, the paint will remain at the surface of the wood and thus will rub off more easily.

- Painters tape

- Tracing Paper

- Exacto knife

Step 2: Prepare the Base and Inset the Compass

I made two indents in the surface of the block:

One was a shallow inset area that's for aesthetic effect only. I carved lines into this area radiating from the point where the string will be anchored and stretching along the hour and half-hour lines (see schematic on the Intro page).

The other is a deeper carved out area for the compass. This second area should have exactly the radius and depth of the compass you have chosen. You can carve out this area in any way that you prefer, but the easiest way would be using a router or a dremel (hand tools can work if necessary). Once the hole is drilled for the compass, place a small amount of wood glue at the bottom and place the compass in it with the North facing towards the top of your block (for the northern hemisphere...think this would switch in the southern hemisphere).

Cautionary tale: Don't forget that North has to point to the top of your block! The first time I put in the compass, I forgot to make sure the N was at the top, so I had to dig it back out (which was tricky, since the fit was so snug). Good thing I got 4 little compasses, so when the first one got all scratched up, it didn't matter.

Step 3: Paint the Pieces

It's not really possible to stain wood in a precise pattern, so I used paint. You could also do some cool stuff with carving or inlay, but I'm not that talented, so I stuck with paint. Some suggest Latex paint as the best to use on wood; I used an oil based paint. Acrylic could be ok if you seal it somehow, but I've found that acrylic tends to just peel off the wood base since it does not sink in.

I made screens out of painters tape and cut the numbers and words out of the tape with an X-acto knife. Then I used a sponge to apply the paint over the pattern where it sticks to the wood only where there is no tape.

The pattern I made on the top was based on the natural pattern on the wood. I thought it looked like a topographical map and, since a diptych sundial is kind of nautical themed anyway, I put an X at the corner where I anchored the string. Tracing paper allowed me to copy the wood grain pattern from the top of the block so my painting could be precise. I used a thick vellum tracing paper, which is stiff enough that it could be a guide for the cutting blade.

Step 4: Make Some Hinges

All of the miniature hinges I found were boring and mostly made out of brass, which I don't find aesthetically pleasing. So I decided to make my own hinges out of aluminum flashing. I decided to make the hinges look like clouds and the front clasp to look like a cloud and a lightning bolt.

To cut the shapes out of the aluminum, you just need a jewelers saw. You'll need to buy blades that are of the appropriate size (teeth spacing, etc) for the thickness of metal you're cutting. Most jewelers blades have some kind of indication on the package that explains what thickness metal it cuts. Jewelers blades are very thin and easily broken if they aren't held very tense. Make sure that the blade is so tense that it rings when plucked, with blades angled toward the handle (so it cuts on the down-stroke). Cut out your desired shape and saw with smooth even strokes trying not to twist the blade. If you haven't used a jewelers saw before, you'll probably break a lot of blades at first, but you'll get the hang of it; jewelers blades come in large quantities for a reason.

Use the pin vise to make holes for the small nails.

If you don't want to go through all this trouble, just either buy miniature hinges or, if all else fails, buy a cheap little wooden box from Michaels or some similar place and take the hinges off. Or, if you have a laser cutter, that could work too.

Step 5: Decide on Your Cities and Prepare the Top

You need to figure out in which cities you would like to be able to tell the time, since the angle of the string must be different for different cities. Ben is from Bellingham and had lived or traveled to LA, Vienna, Delhi, and DC, so those were the five cities I chose. Using the schematic, drill holes at the appropriate height of the sundial's upper inner face.

In order to tell the time, you put the string through the hole and anchor it on the other side at a length such that the string is taut when the upper block is at a right angle to the base. Note that this will only work for standard time, not daylight savings time. If you want to make this accurate for daylight savings time, you need to make additional holes.

With that, you are now ready to tell time!