Bagnold's Solar Compass and application for azimuth tables

This is my version of a beautiful mix of engineering, art and science. This is a Bagnold Solar Compass. People have been navigating using the sun for millennia, but this version was invented in the early 1930's by Major Ralph Bagnold.  The only problem with this type of compass is needing to know the azimuth (angle from true north) of the sun. This changes for every place on earth, and for every time of day! Therefore to use the compass, you had to carry a set of ‘Davis's Azimuth Tables' - which was a huge volume running to several hundred pages. Which, incidentally, you can still buy on Amazon, should you so desire. 

Fortunately these days, we have technology and so I built an app specifically for this project which will calculate the two tables you need to use this compass anywhere on Earth and at any time of year. 

As long as the sun is shining! ☀️

To use your compass: 

First go to the app at: https://sun-azimuth.fly.dev 

Drag the pin to the point on the map where you want to use the compass. Click on Generate Tables. You can then download the tables by clicking the button below the tables. (If you scale the tables to 50% they fit perfectly on an A4 piece of paper.) Print out this page and take it with you. There is a drawer in the base of the compass with room to store the gnomon (the pointy bit) and your tables. You will only need to print the tables once. 

Once you have your tables you are ready to use the compass. 

To work out the current azimuth for your time and location based on the tables: 

1. Find the current month and time for your location in Table 1. Note this value.

    

2. The first table gives you hourly azimuth figures for the first day of every month. If it's the first of the month, just take the figure from Table 1. For each subsequent days of the month, multiply the offset from Table 2 by the current number of days into the month you are minus 1. For example, if it's 9.00am on the 18th April, I take the 9.00am APR figure from Table 1, and the 9:00am APR offset figure from Table 2. I multiply the offset by the number of days (18) - 1 = 17. Then add these two figures together. Be careful - the second figure can be negative! (If this sounds complex, it's not when you have the tables to look at and you've done it a couple of times - promise!) 

    

3. Turn the Azimuth ring of the compass so the value you just calculated is lined up with the red bar at the base of the compass. 

    

4. Keep the compass and azimuth wheel in place, and turn the red course bearing arrow to the direction you want to go in.

    

5. Now rotate the whole compass until the course bearing arrow lines up with the sun's shadow. 

    

6. Your compass is now pointing in the direction of travel, indicated by the red arrow at the front of the compass. 

Here's a quick demonstration (Taken as the sun was rapidly fading in the UK!) 

This is a fun, and genuinely pretty accurate navigation tool and it's a real mix of science and art. 

Printing

There are AMS and non-AMS versions available but you don't need an AMS as all of the colouring is done in separate layers. This also speeds up the print time significantly. You can print as a single colour which is super quick, and the compass is still perfectly functional. 

Supports should be used for the drawer handle. 

You will need a small stick for the gnomon. The hole is sized for a 2mm stick, I found a barbecue skewer worked perfectly (I did spray it black for the looks I'll admit. You could also use carbon fibre rod if you were feeling achingly cool. 

There is a drawer in the base of the compass where you can store the gnomon and the azimuth tables. 

Colour changes: 

Top Ring Plate: 

Start with base colour (brown) 

Switch to lettering colour at layer 12 (black)

Switch to ring colour at layer 15 (white) 

Switch to letter colour at layer 19 (black)

Switch to highlight colour at layer 22 (red) 

Azimuth Disk 

Start with base colour (white) 

Switch to lettering colour at layer 17 (black) 

Hope you like my entry into the Makerworld Hiking Design Contest. ❤️

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https://makerworld.com/en/crowdfunding/273-qwatch-the-customisable-smartwatch