Question Sundials

Last year I did buy a 420 with the idea to create a series of sundials for family and friends as a x-mas present.
I've reported some of my initial progress before and promissed to show you the results.

There was much to learn and I have created several tools (both in hardware as in software) to get this project done. Among the tools I created are

• A method to measure flatness (of the bed and/or or the stock)
• A g-code post processor to correct z-depth, based on the flatness of the stock
• A drilling rig to drill holes at a given angle
• A program to generate sun dials for a given longitude, latitude and motto

The list does not stop here and in the end I did not use all the tools. For instance an endureable material was needed that could stand all kind of wheather. I was planning to work with brass but that proved one step too far. Then I skipped to glass and engracing. For that I had to know the flattness of the surface (I had not found out that there are engraving bits with a spring in it.) Supprisingly, glass is not flat (well, it is within a given tollerance) and I could measure some repeated waves on the surface of it.

Example of a glass sheet measuring about 24 by 20 cm and deviations in z-axis in micrometers.



I could (and did) engrave glass, the results were good but for a sundial it is good for hanging in a window, not for putting it on a surface. The sundial engraving becomes dificult to see.

I ended up with HPL, High Pressure Laminate, which is used as a sheet material in several outdoors applications. It is designed for the outdoors, it is available in several colours and it is hard! It took me some time to go from g-code to the actual dial.


Here is an example of a sundial, first as generated by the design tool.



And as it was engraved and drilled in HPL.

Interesting! But honestly - I'm confused by the number IIX. I thought it has to be VIII ....

Did you have a look at normal wrist-watches using roman numbers? It actually is common to do it "wrong" for dials because of symmetries. You can find normal wrist watches showing
I II III IIII
V VI VII VIII
IX X XI XII
IIII being wrong as well. Only because in that case you have 4 numbers only with I, 4 numbers including V and 4 numbers including X.
For the given sun-dial I'd say they replaced VIII with IIX because of a space issue.

MagIO2 wrote: Did you have a look at normal wrist-watches using roman numbers? It actually is common to do it "wrong" for dials because of symmetries. You can find normal wrist watches showing
I II III IIII
V VI VII VIII
IX X XI XII
IIII being wrong as well. Only because in that case you have 4 numbers only with I, 4 numbers including V and 4 numbers including X.
For the given sun-dial I'd say they replaced VIII with IIX because of a space issue.

As a matter of facts, the romans themself did it 'wrong' many times because they had no convention for it.
The convention where to put the I for 3, 4, 6, 7, 8 etc. is from later times. (And my guess is that it might differ per country.)

The convention I'm used to (has been learned a long time ago) is to minimise the number of I's when combining with something else resulting in:
I, II, III (and not IIV, acceptable but III is not a combination), IV, V, VI, VII, IIX (and not VIII which is alo an acceptable form), IX, X, XI, XII.

I apply this rule also on other combinations.

--Andre.

I forgot to put in details how the dial was made and to show an example of the end result.

Here is a dial with the gnomon mounted.


Material: HPL (a.k.a. Trespa) 20 x 25 cm.
Settings:
bit: engraving, triangle shaped point at 30 deg.
F: about 1 mm/sec.
depth: 0.35 mm (one pass only).
MM-1000 at 1 (about 10.000 rpm)

These settings might not be optimal. The engraving did take some time, 5 hours and 15 minutes, The results are acceptable and I did not take te time to experiment with other settings.

Notice that on this particular one there is some chipping on the top coating at line edges.
This one is made from HPL with a coloured coating in light beige. The side of the chipping is less than the line with and is not too obvious or disturbing the image. It looks like the top layer of melamine is itself formed with thin layers. Might have to do with the process of colouring.
The dial 'Here comes the sun...' is done the same way but has a white top coating and does not show this problem.


Kind regards.