Let's see if I can fix this sundial - rectifying stupid...

WobblyHand

WobblyHand

H-M Supporter - Diamond Member
H-M Lifetime Diamond Member
Joined
Dec 18, 2019
Messages
7,063
So I took home a sundial from my mother's house. It's literally a garden variety cast iron sundial. I kept on staring at it, trying to figure it out. No matter what orientation I moved it, it seemed wrong. Well, today I looked up sundials on Wikipedia and discovered it was manufactured incorrectly.
https://en.wikipedia.org/wiki/Sundial

There's two things wrong, one: the gnomon angle should be angled at one's latitude, and two: the gnomon was attached to the base backwards! Now I could have forgiven the first, but really now, this gnomon was installed 180 degrees from where it should have been! So it never could show the time. I find it hard to believe that this junk gets sold to people. So I'm wondering if I can somehow fix it.
PXL_20240721_133253871.jpg
The Roman numeral XII should be on the same side as the right most tip of the gnomon. As is, it won't show the right time ever, anywhere on earth. The gnomon tip should point to true north (since I'm in the northern hemisphere). I'm at 42.76N, I figure 43 degrees is fine. I put a 45 degree reference next to the gnomon and it's much steeper than that. I'll measure it after I bring it inside. I don't know guys, but this kind of stuff just irks me. Installing the gnomon backwards, gosh, I'm having problems with that... I'll probably blast off the paint later and redo that, but first I need to see how to remove the gnomon.
 
I bought one at our local co-op just because they are cool. The clerk warned me that it wasn’t a real sundial - did not spin or anything.
I used to keep it set to keep time fairly well. Seemed to need to be re aligned every month or so to adjust to solar angle.
 
Last edited:
CJ5Dave said:
I bought one at our local co-op just because they are cool. The clerk warned me that it wasn’t a real sundial - did not spin or anything.
I used to keep it set to keep time fairly well. Seemed to need to be re aligned every month or so to adjust to solar angle.
Click to expand...
I believe if the gnomon is the correct angle, it keeps better time. If you are in a state with daylight savings time - well the sundial knows nothing about that! A sundial doesn't believe in man made concepts - only the position of the sun in the sky.
 
So far, this is easier than expected. I turned over the sundial and found some tape over two spots. Pulled the tape (duct) and found two areas of a sort of rubbery pitch. I excavated it out. I found two threaded studs. And yeah no nuts. They used some rubbery stuff to captivate the threads. Seriously? But that meant, as far as I could tell, nothing else was holding it in. I used two small crow bars and gently applied pressure pulling the gnomon from the dial face. Slowly the gnomon was released from this glue junk. There's glue and corrosion on the threads.
PXL_20240721_152039805.jpgPXL_20240721_152057631.jpg
The gnomon is made of aluminum - it's very light. It's not particularly nice either, at least to me. But it's ok at a distance, if you don't stare at it too much.

Now to ponder making the top lower than the bottom (as pictured) to reduce the angle. It's a hair under 55 degrees now, needs to be 43. Since the gnomon is aluminum I'm at a loss on how to patch or angle the threads. If anyone has suggestions, I'm listening.

Cities at 55N are Moscow, Russia, Copenhagen, Denmark, Newcastle on Tyne, UK, Grande Prairie, Alberta Canada and parts of Alaska. Far north of me.

I'm half thinking of making something out of 5/16" steel or even aluminum. Won't be fancy like the original, but it might work some of the time. Of course, the number markings might be all wrong for here as well. I will calculate what they ought to be then see if they are even close. If they cheated on everything else, who knows if that's wrong as well. Worse comes to worse, I'll simple reverse the gnomon and call it good. Heck, I'll even splurge for some stainless nuts! They look to be maybe #6 or 8, or 4mm or so. Got to measure them.
 
My quick and dirty measurement of the stud, I get about 0.177". Yeah the closest fit to that value is M4.5. Not so standard... That's why there wasn't a nut. I'll go see if there's anything that fits in the shop, but that size is equivalent to a #9 screw, which isn't standard either.

Well, I'm surprised, its actually a slightly rusted #10 stud. The pitch was wrong for M4.5. It came out to be 24 TPI. Cleaned it up and mounted it the correct direction using 10-24 SS nuts. There's no room for a lock washer, just a nut. I could fix that on the mill, but not yet. Still going to look into whether the casting is correct. Might go in the garden as is, if the numbers are in the wrong places. But at least the shadow will be roughly in the right place now. If the casting numbers are ok, (in the correct places) I'll think more about fixing the gnomon angle.
 
Kinda like checking your calculator with pen and paper math.
 
CJ5Dave said:
I bought one at our local co-op just because they are cool. The clerk warned me that it wasn’t a real sundial - did not spin or anything.
I used to keep it set to keep time fairly well. Seemed to need to be re aligned every month or so to adjust to solar angle.
Click to expand...
spin???? WHAT???
 
You must log in or register to reply here.
Back
Top