Latitude as decimal degrees in the range -60 (South) to 60 (North).
Longitude
Longitude as decimal degrees in the range -180 (West) to 180 (East). This is used for calculating daily declinations. If not given, the Greenwhich meridian, 0°, will be used; only very minor discrepancies arising from doing so.
Place
Name of town or other place to be written on the dial plate. If you leave this blank, the latitude will be printed instead.
Thickness
Thickness of the material used to make movable ring of Hour Points. Units are millimetres, in the range 0 (default) to 13. This corresponds to the height of the true (mathematical) dial face above the physical dial plate.
Some General Notes
The PDF file produced by this program has three pages - one for a movable annular part and the associated guides; one for the dial plate; and one and the triangular support that supports the gnomon (filament) plus a tool for checking gmonom angle. An assortment of small circles and rectanges are also drawn. These can be used as wedges, feet, or for whatever purpose you desire. There is no printed part for a gnomon - you will need a length of fine thread or or other filament for that purpose.
The design assumes the dial will be laser or CNC cut, or scroll-sawn, from a rigid material such as Baltic Birch ply or metal sheet. Red lines indicate where full depth (piercing) cuts are required, blue lines are for etched (shallow non-piercing) lines, and black is for text (which, on a laser cutter, corresponds to rastering). Note that a tiny pinhole should be cut at the center of the dial plate (a tiny red circle, almost a dot, shown in the PDF page 3).
The drawing is always 200mm by 269mm. These dimensions give the largest possible drawing that can be fitted within all of A4, US Letter and Canadian Letter stationery allowing for a 5mm margin on all edges.
You can use a PDF editor or other drawing software to modify the drawing as required to add your own artwork. As well, if you're working with pieces of stock material that are bigger than the drawing size used, you could move elements around for more efficient use of material.
If you decide to resize the drawing you must maintain the original aspect ratio but you will need to adjust the value you give for the thickess parameter - scale it in the opposite sense to that you apply to the drawing. For example, if you scale the drawing up by 2, you will need to give a thickness value that is half of the actual value. This counteracts the implicit z-axis scaling that would happen as you resize the drawing.
For latitudes greater than about ±45° the support height will become increasingly unweildy. You may want to come up with a different way to support the gnomon filament.
For latitudes greater than about ±55° the support would be too big to fit within the size limit for the drawing, so it is deliberately shortened. Installation will require tilting the support towards the centre of the dial to get the required filament angle.
Safety warning: At the time of writing, I have not tested my example dial through a full annual cycle - some mistakes in my code may remain. Please check that any dial you generate is consistent with the layout you would expect.
For high precision work, you'll need to modify this web page to reflect the smallest size of pinhole that your equipment can create. You'll need to play around with the constant named 'centre_hole_adjustment', and the statement where it is used. Feel free to contact me for advice relating to this.
Assembly
The finished dial will be something like the photo shown below.
Glue the guides for the movable ring in place. They should be on the outsides of the pair of parallel lines etched on the dial plate. Make sure that there is just enough leeway to allow the ring to move freely.
Tie a small loop in the end of a piece of thread and hook it round the small notches at the top of the dial. Run it underneath the dial plate then thread it up through the pinhole at the center of the plate. One of those little wire devices for threading needles is helpful for this step.
Now, holding the support with its foot along the transverse line etched in the plate, run the thread over the support, seating it in the notch at the top. Bring the tread back down to the top end of the dial plate. Run it through the centre notch of the three at the top of the plate, pull tight and then wind it a few times round and round the other notches to secure it.
Make sure the foot of the support is centered on the transverse line, then use the rectangular tool to check and adjust the angle of the thread. Once you're satisfied, you can apply a tiny drop of water-soluable glue to the top of the support to lock the thread in place. Optionally, to help anchor the foot of the support in place, you can glue on some of the small buttons and other little shapes.
Install the dial in situ, with the meridian line directly towards the pole. The dial plate has a meridian line which you can use at local solar noon to check alignment. You'll also need to check that the dial is perfectly horizonal for both North-South and East-West axes. A bull's-eye level and some very thin wedges will help.
Set the pointer to today's date, and read the hours to sunset. The date scale has longt ticks for the first day of each month; medium ticks for the 6th, 11th, 16th, 21st and 26th days; and short ticks for the other days. Note that the pointer tip should be at the day's tick - not in the gap between ticks.
Steve Lelievre, 2016. You are welcome to use this web page (and the associated Javascript) as is, or modified for your own purposes (in which case please retain comments acknowledging original authorship).
