Sun Clock

I'm not sure is "Sun Clock" is the best name for my clock. Maybe someone will have a better suggestion. I'm entering this Instructable in the Clocks Contest so if you like it please give it a vote. I just very recently made this clock and didn't take pictures during the process but now see there's a Clock Contest.

Here's the concept behind this clock. It's obviously a 24 clock. 24 hour clocks are not very common, and when you see them, "0" or "24" is usually at the top but on mine it's near the bottom. Since my clock is mounted on a South wall in my house, the Sun comes up in the East which is roughly where 6:00 is and goes down in the West around 18:00 and noon roughly straight up. So the hand of my clock sort of points at the Sun is (in one plane). In my opinion, a clock like this makes more sense than any other clock format and might be the easiest for kids to learn time?

Why is the clock face crooked? I live in Austin, TX which has a longitude of about 97.7 W. I'm in the Central time zone of the United States. Austin is currently in Central Standard Time (CST) which is UTC -6. But if I think about that 6 hour offset from UTC in terms of degrees of longitude, (360 degrees/24 hours = 15 degrees/hour) so 6 hours * 15 degrees/hour = 90 degrees. But since Austin is at 97.7 and 97.7 - 90 = 7.7 it means Austin is almost exactly in the middle (15/2 = 7.5) of this timezone which means solar noon (or meridian) is at about 12:30. So if I rotate the dial on my clock about 30 minutes counter-clockwise the hand should point to the Sun. But it turns out that astrophysics isn't quite that simple and several factors change what time solar noon is throughout the year. Today in Austin solar noon is at 12:42. But 12:30 is close enough for me so I'm not going to be adjusting that throughout the year.

But what about daylight savings time? Simple. On this clock, the face is mounted in a way that allows me to rotate it. So March 12th, 2023 I would rotate the face one hour counter-clockwise. So then 13:30 is straight up and the hand still points to the Sun's location.

Another interesting concept in this clock is that when solar noon is straight up, sunrise and sunset should be evenly balanced on either side of that. I laser etched "Sunrise" and "Sunset" on some clothespins and clipped them on. I'm trying to come up with a nice way to automate showing those times and maybe markers for Winter Solstice, Summer Solstice, and the Equinoxes.

Where's the minute hand? The 24 hour clock motor I used was from a timer and thus didn't have a minute hand. I'm OK with that for several reasons.

1. The minute hand doesn't fit the concept of pointing to the Sun
2. Each hour on a 24 clock is 2.5 minutes, so you have to make another scale for minutes compared to most clocks
3. Since this clock is rather large (38" across) you can tell the time down to the nearest 5 minutes pretty easily. If I need to know the time more accurately than that I'll look at my phone.

What's the weird Earth map thing? I stumbled across something called an Azimuthal map while working on this clock. You can generate them from different starting locations using this site NS6T's Azimuthal Map. In my case, its the Earth from the North pole, almost all the way down to the South pole. I thought having Antartica going all the way around the outside was distracting so I cut the circle smaller but I think I'm going to remake it and leave Antartica in place. In my case, I have Texas straight up (this circle doesn't turn). So as the hand moves around showing the current time for my location it also indicates where the Sun appears to be around the Earth. Like the clock hand, this Earth map doesn't change for daylight savings time either.

Supplies

The clock motor is really the only rather specific supply you really need (see next step). Everything else can be of your own design and based on the materials you have available and the look you want.

I used a large Laser at my local maker shop Asmbly | Austin's Largest Nonprofit Makerspace to make the clock face and the Azimuthal map out of thin plywood, but you would really make them out of any material and tools you have access to.

Step 1: Clock Motor

For my clock motor I used one of these heavy duty Intermatic 24 hour timers. There are small battery powered 24 hour clock motors available, but if you're making a large clock you just need to be aware that a large clock hand requires a little more torque. In theory, if you keep the hand lightweight and/or balance the clock hand it shouldn't be a problem. But I knew this kind of AC powered timer has enough torque to switch a pretty strong spring mechanism.

There's just a spring clip holding this timer in the metal box. You can also buy just the replacement clock mechanism.

There's a manual switch lever which sticks out above the yellow clock face and I used my Dremel tool to cut that off so the hand I added on wouldn't hit it.

I didn't worry about the orientation of the clock motor (which way was up) but instead just found the best existing holes in the metal that I could put a couple of screws through into my wood support.

Step 2: Clock Face

I initially struggled with how to design the clock face and have accurately positioned lines and numbers. I asked some questions on my maker shop forum and someone quickly described how LightBurn had a "Array Rotate" function that lets you make a number of copies of an element rotated around a circle. I downloaded (trial license) and I used that feature a bunch of times to make all the marks and the numbers around the dial. There's a choice in that feature to rotate the elements that you're copying or not. I chose not to rotate the numbers but since I rotate the face some amount I'm now thinking I should have rotated the numbers so they all point outward instead up upward. I'm sorry I can't illustrate that feature better for this Instructable but the trial license ran out and not sure I would use the software enough to buy it yet.

The largest Laser at Asmbly | Austin's Largest Nonprofit Makerspace has a working size of 39" x 63" so I made my clock face 38" diameter. I also considered making a bunch of pie shapes and gluing them together. In that case I could make it even larger. I used some scrap of the same plywood material to do some tests and it's a good thing because with too much power the "engraving" was burning all the way through!

The other thing I discovered is that the Laser tends to char the wood around the engraved part. One solution is to cover the wood in a contact paper before burning and then peel it back off when done. It turns out I had some wrinkles in the contact paper and so I did get a little bit of charring. I could sand it off but my wife thought it added some character to it.

To mount the clock face I used some screws which had something like a built-in washer under the head. So the clock face just rests on those which allows me to grab the face and rotate it. There's a third one of those screws near the clock motor to hold it all in place.

I haven't put any finish on the clock face yet. I think I might use a clear polyurethane.

Step 3: Clock Hand

I happened to have some 1/4" thick black foamboard laying around. I found an image of a nice clock hand and enlarged it for the size I needed. I cut it out on my home Snapmaker Laser. I could have made it out of the same thin plywood and the clock face but this foamboard is super light and so I was able to stick it to the yellow timer clock face with some double-sided tape.

Step 4: Azimuthal Map

This part is really just decorative and doesn't play any part in telling the time. But I needed something to cover the hole in the clock face that I needed to create for clearance of the timer.

The website is here https://ns6t.net/azimuth/

The timer motor I used had a pointer which doesn't move so I just unscrewed that and screwed this map in it's place.

Again, this part doesn't turn. Texas is straight up because it represents my position (longitudinally) on Earth.

Step 5: Summary

It's big. The bigger it is, the more accurately you can tell what time it is since this clock only has the hour hand.

It's on a South wall in my house. It wouldn't mean as much to me if it were on a different wall because it wouldn't point towards the Sun. Thanks for reading and I'd love to hear anyone's comments on my clock!