There is something about a sundial that conjures up an earlier era. It is a simple tool that requires no attention to provide that most useful piece of information; the time of day. Old-tech is almost high-tech when you consider all that goes on to cast a shadow at the right time.

In the past I built an outdoor garden sundial . So now I thought it might be fun to bring the outdoors indoors so I created this windowsill sundial for your south-facing window. It is a horizontal sundial. There are many types of sundials, see 3D Challenged's Paper Sundial Kits instructable for examples of many other types of sundials.

This windowsill sundial is much easier to construct than the garden variety and should perform just as well.

Have fun creating a memento of yesteryear.

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Supplies

Materials:

Plastic Cloche (Bell Jar); 5.7" x 3.6" dia (the larger of two at Dollar Tree store)
Plastic Sheet; black foamed PVC sheet 0.2" (5mm) thick, 3-3/4" square
Three #2 x 3/8" brass wood screws
0.06" (1.5mm) dia x 3.7" brass rod or tube (length may vary depending on latitude)
Sundial face printed on paper or cardstock

Tools:

Saw to cut out disk (I used a bandsaw but a coping saw would do)
Drill motor and 1/16" bit
Protractor
Sandpaper
Scissors
Screwdriver
Black and Silver felt marking pens
360 degree bubble level
Magnetic compass
Masking tape
Scrap Cardstock
Diagonal cutters (not shown)
Angle gauge (optional)

Step 1: Cut Cloche (Bell Jar) to Size

I wanted a large diameter cloche, but with large diameters came large height. Since the cloche is plastic I decided to cut it down to be shorter. In fact I cut it down as shown in the photos and then decided I needed to cut it down again. I ended up cutting off about 1.4" in total off the bottom. The finished size was about 3.4" in height.

To cut the cloche I wrapped the cut area in masking tape and then used a rectangle of cardstock to make a template to draw the cut line around the bottom rim.

I made the cut using a bandsaw. The cloche has tapered vertical walls (draft angle for plastic molding) so I needed to place a piece of cardstock under the domed end to shim it up a bit so the cut would be parallel to the plane of the original opening.

Step 2: Cut Sundial Disk to Size

The sundial's markings are on the sundial disk. The disk is separate from the base since the disk and markings need to be level for accurate timekeeping. I took the scrap that was cut off the bottom of the cloche and used a silver pen (I'm writing on black plastic after all) to trace a circle for the sundial disk onto the black foamed PVC sheet.

Using the bandsaw again, I cut on the inside of the line to provide a bit smaller disk, leaving extra space between the disk and the internal wall of the cloche when assembled. I sanded the cut smooth with some sandpaper.

Step 3: Determine Latitude and Cut Template

Information about our physical location is key to a successful sundial.

You need to know your latitude; your location 'between' the equator and the North Pole [or South Pole for those living below the equator] as this is the angle above horizontal that the gnomon (the pointer of a sundial that casts the shadow) needs to be mounted at.

You can find your latitude on many phone and computer applications. The latitude reading is given with a North or South (below the equator) designation. The Compass App on the iPhone will give the latitude. You can also enter your address on the magnetic declination NOAA website and it will provide you with your latitude. We will be going back to this site in Step 7 so why not use it now? My latitude is 40.5 degrees North.

We will be mounting the brass rod (gnomon) at an angle equal to your latitude. In order to make it easier to drill a mounting hole we will be making a template out of some scrap cardstock. Use a protractor to mark the angle of your latitude. My compass was turned over, but I marked a 40.5 degree angle (my latitude) and cut out a 40.5 degree triangle. I wanted the template to be shorter than the drill bit so I held it against the drill bit and cut it off appropriately.

Step 4: Drill Gnomon Mounting Hole and Mount

Align the drill bit with the 40.5 degree template and drill a hole about 1/8" from the edge of the disk. Insert the brass rod and check your angle with the template. You may want to use some glue to secure the gnomon in place.

The gnomon needs to be a length so it will fit into the cloche. Take a square (90 degrees) and project the edge of the disk up onto the rod, mark it, and cut it to length.

Step 5: Determine the Markings on the Face of the Sundial

The markings on the face of the sundial are also affected by your latitude. Information regarding the angles of the hour (and other) lines can be found on the HORIZONTAL SUNDIAL SHADOW ANGLE CALCULATOR website.

I only used the hour information as the sundial is small.

I took the degree information and used Fusion 360 to draw the hour lines in accordance with the angles given.

I did a screenshot of the Fusion 360 drawing and pasted it into a graphics program to add the hour numbers and the North indicator.

Step 6: Print and Cut Dial Face and Install Leveling Screws

Print out your sundial face markings and cut out the disk. The face/disk needs to be level for a horizontal sundial to work correctly so I installed three #2 x 3/8" brass leveling screws in the holes drilled as shown. [Note that the hole location in this photo is a bit to far from the gnomon to give good stability. Place the hole closer to the gnomon location; at the 5 and 7 hour lines. Look at other photos for better screw placement examples.]

The brass screws give the sundial a nice 'earlier era' look and are nonferrous so they don't interfere with the magnetic compass readings taken in the next step.

Step 7: Level and Orient Sundial Face

Place the sundial where you want it located.

For a horizontal sundial to work it's face must be horizontal; i.e., level. (Here's were those brass leveling screws come into play!)

Set the bubble level on the face of the sundial and use the 3 brass leveling screws to get the face level; the bubble in the center circle.

Another requirement for a horizontal sundial is that the gnomon must point North.

The sundial must be oriented exactly North, true North (in the Northern Hemisphere). Not the 'North' a magnetic compass points you to, but TRUE North. Magnetic North and True North are not the same thing. They differ slightly.

True North is where the North Pole of the Earth is located. It's fixed. Magnetic North is based on the magnetic field of the earth and has a location that is near, but not at the North Pole and has the tendency to wander slightly over the years - You want True North.

You can use a compass to determine True North, but you will need to know your magnetic declination, which is the difference between True North and Magnetic North for your location. You can go back to the NOAA website and enter your street address (right hand box) to find out your magnetic declination for your location.

The declination is added or subtracted from magnetic North depending on whether you are East or West of the Agonic Line (where magnetic North points True North) to identify True North at your locale. My location required I add 11 degrees to magnetic North to point me toward actual North Pole of the Earth. If you want a more in depth explanation you can visit my garden sundial instructable.

Lining up the lines on the compass with the North line (noon) on the face of the sundial I adjusted the magnetically pointing North needle to 11 degrees off center.

Now my sundial is level, and pointed to True North and ready to tell time!