2025-05-11

Last modified: 2025-05-21 11:42:06

Sundial

This is a good tool: https://tpeach90.github.io/sundials/

I think I can "prototype" my sundial by printing it out on paper, and using a 3d-printed gnomon, and then if I'm satisfied with it then engrave in metal and mount on some sort of column.

What is the best tool for laying out the dial? I started doing it in Inkscape but I find Inkscape too infuriating for technical drawing:

1. circles are positioned by the bottom-left corner instead of the centre
2. line thickness counts towards the width/height of an object
3. line thickness changes when you resize an object

In my mind all coordinates should work as if the line thickness is 0, and then line thickness is a property you specify separately. Line thickness is just to do with how its rendered, not a fundamental property of the shape.

And positioning circles by their bottom-left corner is just insane.

So I could try LibreCAD? I remember from the douzieme scales thing that LibreCAD is very annoying.

ChatGPT suggested trying SolveSpace, I've never used SolveSpace for 2D CAD before. Let's give it a go.

The longest day is the summer solstice. In local solar time, sunrise and sunset ought to be symmetrical about noon. And on the summer solstice, I think sunrise is at about 4am local solar time and sunset about 8pm. So if the sundial covers 4am to 8pm then it can indicate all possible lit times.

If my gnomon is 3mm wide I think I need to basically split the dial and have a 3mm gap in the middle. Because in the morning one edge is the gnomon and in the afternoon the other edge.

My provisional gnomon has a hypotenuse length of 70.67mm, which is 55mm above the dial plate and 44.38mm away from the centre.

SolveSpace is OK, not as good as FreeCAD. Can I export a FreeCAD sketch as an SVG?

Oh, neat. "File -> Export -> Flattened SVG". This is the way to go then.

Seems like either the gnomon or the hour marks are too short.