Full disclosure, I came upon this instrument at the Following Kepler blog. He made one from scratch and I thought that I might be able to improve on his a bit.
It’s a nightmare cutting a circle out of metal unless you have some specific equipment that I do not. These days however, there are a multitude of online businesses that will do just that for you. After looking at several I chose SendCutSend because they have an app that you can basically draw the piece with online. They offer many different metals and other materials. I was originally looking at brass but its expensive, so I opted for 3/16” aluminum for $91.
The pieces arrived within a week and they are just about dead on the money dimensionally. I think they used a laser to do the cutting. They have an upgrade where you can have them deburr the part which I opted not to do. It only took me a few minutes with a file and sandpaper and I had the two pieces fitting together quite nicely.
After a couple of attempts to put the tick marks on the outer ring using a protractor a better idea dawned on me. I laid it out in Autocad and printed it and then taped that down to the ring. Then I put the tick marks in using a chisel. That worked out well.
I have the pieces of the dial on temporarily with double sided tape. They are just pieces of wood. When I have figured out exactly how I want it to be I will put some metal parts on permanently with screws.
Test Run
I have it temporarily mounted to a post and I tried it out this morning. I was going by a latitude that’s a bit south of here but it was reading fairly close. The pic below shows the angle at about 8:40 a.m. that should have been about 43° and this was right on 40°. Not plumbed and I am actually a bit north of that city’s latitude I was going by.
I need to figure out how the size and shape of the “pointer” affects things. I do not think the rear pointer is even necessary other than helping to hold the plates together. I will probably add a plumb line to it as well.
Real World/Sphere World
Even something this simple shows that Earth is spherical. You could go either north or south a couple of hours and at the same time of the day the reading would change due to the latitude. It should read precisely the same if you went east or west as long as the local time was the same.
So in theory you could have a dozen of these at various places around your region and then at given times write down the reading and then compare notes later on. You would then be able to deduce a) Earth is spherical and b) the size of the sphere I’m pretty sure.