Introduction: Custom, Functioning Sundial Wristwatch TJT2/6

This Accurate Sundial Wristwatch is Time-Journey Tool 2 of 6. Heraclitus described time as a river rushing toward us. 3d Printers speed up the river, but at what rate? The right time tools help us understand and control our destinies. They connect us the earth and its natural rhythms. 

Determining time of day by the Sun's angle is a convenient, presumably prehistoric art. We see them from time to time, but sundials are rarely at hand, let alone configured for accuracy. Both primal preppers and anachronistic astrophysicists can proudly wear this one on the sleeve.

Sundials mark the time of day by Sun-ray shadows cast by the dial's sharp-edged, angled gnomon. (pronounced as in "no mon, dis Marley cd is legit") The top edge of the gnomon is set parallel to the Earth's axis of rotation. The Sun's daily arc across the sky moves the shadow's edge across hour markings from which the time of day is ascertained.

Recommended Materials and Processes:

 Computer with internet access
 3d modeling software (or download my 3d model for free)
 access to a 3d printer (I use
 a watch band

Step 1: THE DESIGN: Easy or Hard Way?

I'm sorry to say decorative sundials are typically inaccurate. A sundial needs to be configured to a particular latitude and longitude. 

In 1989 Back to the Future Part II, the bully tells poor Marty McFly, "we can do this the easy way or the hard way!" Then a character named "3-D", of all things, hits McFly over the head. Same here. To make a sundial you can do it the easy way or the hard way. Download my design for free. That's the easy way. Do the trig and the 3d modeling yourself, that's the hard way. Your choice, McFly.

If you want to go with my design, continue to STEP 2. It'll work fine, just properly tilt it if you're at a different latitude (I'll explain). Make sure you account for daylight savings time, if necessary. 

If you want to make your own 3d model for your sundial skip to STEP 3. 

Step 2: My Design

If you decide to use my design. Here's a screenshot from where I designed it in Rhinoceros 4.0. The .stl file can be downloaded for free at:

If you wish to 3d-model your own 4d hypercube, you might already have 3d-modeling software.  If not, some excellent, Free 3d-modeling software can be downloaded at:

You can get Rhino's evaluation copy at:

My Rhino-created model has 233 individually-modeled component pieces. A tutorial of its creation steps in Rhino would be too long for an instructable. If you'd like instructions in 3d modeling, I am uploading two rhino modeling tutorials. See "3d 4-Dimensional Tesseract Hypercube", Models A & B.

North/South Adjustment:(if you download my design & 3d print it as is) You'll need to tilt the sundial south one degree for each degree of latitude (about 69.06 miles) you travel north above my latitude: Durham, NC, USA Latitude: 36.06. Accordingly, tilt the sundial north, for each 69.06 miles south of my location. This keeps the top angle of the gnomon parallel to the earth's axis.

For example, if you're at 40° N latitude in either Columbus, Ohio or Beijing, China, tilt it 4° toward the south. In Prague, you'd tilt it 14° south. If you're in Los Angeles, California tilt the sundial south 2° north. In Memphis tilt it 1° north. This adjustment will keep the gnomon's top edge aligned to the Earth's rotational axis.

East/West Adjustment:(if you download my design) For each East 14 miles due East at my latitude (within my time zone), the sundial would read 1 minute slow. Likewise, 14 miles due West, it would read 1 minute fast.

You can easily determine your own latitude and longitude here:

Step 3: The Math

Okay, McFly, you've decided to do it the hard way. Here's the secret: YOU don't need to do the trig! Our instructabrotha Alexander R. Pruss has made a calculator to do so for you. To construct your own custom-configured sundial to your particular location, here's how:

First, get your own latitude and longitude at this site:

Pruss has written an online sundial calculator that will immediately do all the math-strophysics for your current or favorite place on earth. Eratosthenes would be proud. Go to his website (Pruss', not Eratosthenes'):

Type your info into the calculator. The calculator automatically produces a PDF to make a paper sundial. It lays out the exact design according to your latitude/longitude (or zip code). 

Print the automatically-made PDF on regular printer paper or card stock.

Step 4: Cut & Assemble Paper

Cut out the PDF file and assemble it. Even if your plan is to build a 3d model in a 3d modeling program, it's fun to print out the paper version. The PDF shows three shapes, the round disc, a triangle, and a folded-up gnomon structure. The triangle is key. It tells you the gnomon angle for your latitude. Make sure that's the final gnomon angle on the round disk.

If you want more detailed, hand-holding-type instructions, go here:

It's pretty straightforward though.

I should include Pruss' caveat. Here 'tis:

The script currently works for latitudes between 24 degrees (north or south) and 65 degrees (north or south).  (That covers all of the contiguous 48 states in the U.S., much of the populous parts of Canada and Europe, all of South Africa, much of India, etc.) The limitations are due to the way the gnomon is designed to work both when shadows are short and when they are long, and its having a wider base.

Step 5: Craft It by Hand?

The PDF sundial generator has done the hard work.  Once you have that, there are two different ways you can proceed to make your sundial wristwatch. (Remember, I told ya you could use the 3d model I created. That's certainly the easy way.)

Now that you have the paper sundial, one route is to make a sundial by traditional craft skills. The other option is to create a 3d model & get it 3d printed. 

If you choose the traditional craft route there's no limit to materials. You can use the accurately, locally-configured paper sundial as blueprints.

Congratulations, here's your walking papers, go be fruitful. If you're a baker you can make a sundial out of cookie dough or pizza crust. You can use play dough, Sculpey®, concrete, titanium, wood, LEGO®, bricks, copper sheets, glass, ice, leather, asbestos, epoxy, fingernail clippings, marble, terracotta, butter, or limestone. Perhaps others.

If you want get a model 3d printed, then proceed to STEP 6.

Step 6: Model It

If you can 3d model it, now is your chance. Otherwise, download the 3d model I created here:

Step 7: Print It UP!

Determine your final material: bronze-infused stainless steel, nylon, silver, etc.

Configure the thickness of your model for the intended material. For example, nylon can be .7 mm thick. I usually model them at .85 to make sure Shapeways' auto-check software doesn't reject them. Stainless steel should be 3 mm thick.

Shapeways offers bronze-infused stainless steel. I had mine printed in that and also high-detail nylon.

As a wristwatch, this bronze-infused stainless steel sundial is probably good to any earthly ocean depth or freeze-thaw cycle.

Step 8: Attach It

Attach the strap or wristband.

As Jimmy Buffett memorably put it in '77, 'changes in latitudes, changes in attitudes', affect sundials as acutely as rum drinkers. Sundials are more mathematically predictable, moment to moment. 

Typical orbiting satellites moving at 20,000 mph lose 2/100ths of a second per year due to relative time travel. They make time-traveling adjustments every day. Clocks get out of sync in the process of time travel. Sundial wristwatches do not. They're more accurate that way. Get off your axis and make one.

Time-Traveling Cosmonaut/Chrononaut Sergei Avdeyev has aged about 20 milliseconds less than typical Earthlings. Google it or go to wikipedia. Time Travel is a fact. To join the Sergei & the Chrononauts, (great name for a band) you need tools. Here's Time-Journey Tool 2 of 6.

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