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3D printed sundial whose precise holes cast a shadow displaying the current time (mojoptix.com)
839 points by edward on Feb 13, 2016 | hide | past | web | favorite | 92 comments

Interesting, on the Southern hemisphere, the sundial needs to point to the South Pole and the design needs to be altered:

"in the Openscad script you can set a flag that will simply rotate upside-down the whole swiss cheese inside the gnomon, and build a ‘Southern-hemisphere’ version of the gnomon. This way, the ‘roo can simply use this Southern-hemisphere sundial exactly the same way a cow or a penguin would use their Northern-hermisphere version the sundial, with just one difference: the ‘roo will have to point the tip of his sundial toward the South Pole." [1]

[1] http://www.mojoptix.com/2015/10/25/mojoptix-001-digital-sund...

> a cow or a penguin would use their Northern-hermisphere version the sundial

But penguins live in the southern hemisphere. Conspiracy?! Maybe!

It must be a Galapagos penguin: https://en.wikipedia.org/wiki/Galapagos_penguin

A YouTube commenter offered a possibly more plausible explanation:

> Angela Brett 1 month ago

> +Tainer Waynes Maybe he confused the English word penguin with the French word pingouin, which means auk (a bird similar to a penguin which lives in the Northern Hemisphere.) The French word for penguin is actually manchot. :)


An auk has a black beak, the penguin in the video is of the orange beaked cartoon type of penguin.

Maybe, but as a french speaker I can confirm that it's easy to confuse. I just learned that Pingouin and Penguin are not the same. There is even a whole section explaining more subtleties about why it's often missuses in the french language.

Confusion habituelle

Par abus de langage, le pingouin est souvent confondu avec les manchots, des oiseaux de la famille des sphéniscidés qui vivent dans l’hémisphère sud et ne volent pas. La principale raison de cette confusion est la ressemblance avec la plus grande des deux espèces de pingouin, le grand pingouin.

Une autre source d’erreur est la parenté étymologique entre le mot français pingouin et celui désignant les manchots dans les principales langues européennes comme pinguïn en néerlandais, pingüino en espagnol, Pinguin en allemand, pinguino en italien, penguin en anglais, пингвин (pingvin) en russe, ou encore pinguim en portugais.

Dans de nombreuses langues, deux termes différents sont utilisés pour désigner les deux espèces de pingouin, ce terme n’a donc pas de traduction exacte. En anglais, le terme Great Auk désigne le grand Pingouin, auk étant un terme générique désignant le plus souvent l’ensemble des alcidés. Le petit Pingouin est quant à lui appelé razorbill. En catalan ou en italien, respectivement les termes de gavot et alca sont en revanche utilisés comme en français pour désigner les deux espèces.

The Oxford dictionary has an entry on the origin of the word penguin: http://www.oxforddictionaries.com/words/what-is-the-origin-o...

And they made a short video on the same: https://www.youtube.com/watch?v=M09oIwSQ6q4

This point is addressed by the inventor in the comments at TFA:

  Ernest Shackleton
  October 29, 2015 at 10:21 am	

  Penguins at the North Pole??

    October 29, 2015 at 10:56 am	

    If you were a penguin on a touristic trip, where would
    you go for the Xmas holidays ?

What if you're on the equator?

use the northern-hemisphere sundial stick, arrange it parallel to the ground and "top" pointed north

(or use the southern hemisphere sundial stick and point it south. this just swaps what end the base is on.)

Would you not align it parallel with the equator, and therefore get a more squished (horizontally compressed) time display?


Also, I encourage everyone to donate to the guy, which you can do here: http://www.mojoptix.com/donations-page/

What he is doing is just so wonderful and inspiring in so many ways, and to top it all off, he's doing it without muddling up his content with ads and other gimmicks. Please repay him for what he is so selflessly giving out for free and without strings attached. (He is sharing all files, all 3d designs etc... of such complicated things, a lot of people don't do that, so this guy is just super brilliant). I don't make a lot of money but I'll be giving him $50. I hope you can give even more. :)

Ok, we changed the URL to that from http://boingboing.net/2016/02/09/a-digital-3d-printed-sundia.... Thanks!

Skip the intro and see it in action: https://youtu.be/wrsje5It_UU?t=12m58s

I found the explanation of the technical challenges well done and worth the time.

Probably just as impressive is this (patent just expired) digital sundial: http://www.digitalsundial.com/

Very, very, cool. This got me searching for other implementations of a digital display sundial.

This one is interesting...uses a mask of slits http://www.fransmaes.nl/genk/welcome-e.htm (iframes, ugh...click #8 in the left sidebar)

Edit: Another cool implementation http://www.voshart.com/SUN-CUBE-prototype

I bought one of those a while ago, very clever.

They are sold at http://www.digitalsundial.com/

Wow, this site took me back to 1995.

Can anyone tell me how OpenSCAD compares to something like SolidWorks for designing objects? I'd much prefer to learn something open and programmable, but if SolidWorks is much easier to use for common cases, then I'd go with that.

I've never used any 3D designing program other than SketchUp.

I've only ever used FreeCAD and OpenSCAD. I assume SolidWorks is something like FreeCAD, an interactive 3D editor. Out of the two, I'd pick OpenSCAD any day. Here're some reasons:

* If you're a programmer, the learning curve of OpenSCAD is almost non-existent. Assuming you're familiar with 3D modelling concepts, it should take an hour or two to go through and play with the entire feature set of OpenSCAD [1] (which I did).

* It's simple and the defaults are sensible.

* Your model is basically a line based source file which can be put under git and improved through pull requests, etc.

* Your model is easily made parametric. Last model I made was a tripod mount where I could simply change the angle of the legs or wall thickness and everything would adopt.

* OpenSCAD can be used as an 2D vector modeler as well. For me, it's replaced Inkscape 90% of the time.

There are however things that are not as easily doable with OpenSCAD. One feature lacking is constraint solver so you have to do some back of the napkin trig for such things. I've also found it non-trivial to simply "chamfer" an edge, like I could in FreeCAD.

[1]: http://www.openscad.org/cheatsheet/

For Windows or WINE, open source (and parametric) Solvespace [1] is also excellent and is kind of a middle ground between OpenSCAD and Solidworks/Inventor/Pro-E/Catia etc.

The prog is fast, fully portable (as in "can run from usb drive") and tiny (~2MB iirc). Also has a wealth of export options including g-code for cnc, though prolly pretty rudimentary for 2d routing.

There is a good active fork of Solvespace on Github [2]

[1] http://solvespace.com/index.pl

[2] https://github.com/whitequark/solvespace

The fork also supports Linux

oh, nice. "portable" in every sense of the word then.

That's very interesting, thank you!

I tried using OpenSCAD to design a mug to be 3D printed as a family Christmas present recently. It seemed to me like there were missing tools. Up until now I've done my hobby "CAD" work using the Diagrams library in Haskell. It works really nice for 2D work that will get sent to a laser cutter. The 3D portion of Diagrams though is still under development. So I tried working with OpenSCAD. I think if I were doing more traditional work it would have worked out ok. There were 2 basic issues I ran into.

The first may have been just my wimpy computer but as I approached what I wanted the whole process got slower and slower. Some of that could be combatted by adding tunable resolution parameters to keep the number of polygons down. It should be pointed out that OpenSCAD doesn't really do curves. Everything is polygons which at least in the roughing you design out phase are rather visible.

The second issue I ran into is that some of the way things are done makes it harder to work than you would like. Complex data structures aren't really a thing. If I remember rightly there are arrays but nothing more complex. You can't iterate over the points in a shape. There doesn't appear to be a way to extract dimension data from a shape. CSG is nice but sometimes you want more.

These may not have been that much of an issue if I were doing something different. Trying to wrap a 3D model around another non-uniformly curved 3D model just isn't really what the tool was designed for. And to be fair, I couldn't get AutoDesk's free tools to do what I wanted either. That is probably due partially to a lack of experience in the area and probably pushing the tools to do things they just didn't have in mind.

Yeah they're not remotely comparable. For 99% of CAD stuff SolidWorks is far superior. It is only with occasional tasks that are generative or highly repetitive that you would sanely want to use OpenSCAD.

Examples of when you'd use OpenSCAD:

* Computational art (e.g. convert a photo into some 3D model, print a sound wave, etc.)

* Gears, sprockets, etc.

* Fasteners (nuts, bolts, screws, etc.)

Examples of things you would be insane to use OpenSCAD for, and should definitely use something like SolidWorks:

* Motorbike

* Cordless drill

* CNC machine

* Well pretty much everything except the stuff I listed above

There's also the point that SokidWorks costs $4000 minimum! (Excluding the student license).

For many purposes, such as the author sharing his designs with random viewers, that makes it a non-starter.

An alternative commercial program (not OSS), but free for Hobbyists is Autodesk Fusion 360.

It does have significant drawbacks... but if you're just getting into CNC stuff, it has fairly decent CAM functionality in built, making it a reasonable intro thing. :)

Absolutely second this. Fusion 360 is far from perfect but it does provide some approximation to real parametric modeling. OpenSCAD lacks very basic features by comparison (e.g. you can't even make real cylinders). I forget the exact licensing terms (I'm using an edu email address), but they basically seem happy for it to be used for free for non-commercial purposes. I think the pricing is quite reasonable in any case.

Hmm, it looks like that's only free for 30 days?

It shouldn't be. It's supposed to be for 1 year, and be renewable. I've been using it on and off for a few months now, without issue, if that helps. :)

You're right, they mention somewhere you open up the trial and select "I'm a hobbyist" and it becomes free, thanks!

Yeah, I guess I should have added this to the question. I just started making hardware designs, so I want to make simple things like boxes to put my hardware in, or other sorts of enclosures. Nothing as complicated as a motorbike, just boxes with at most a few parts.

Plenty of good (considering their costs) 3d-printers designed in OpenSCAD, which are a kind of CNC machine.

OpenSCAD is completely prorgammatic. You write scripts to generate solids and manipulate them. There is no graphical editing. With something like solidworks most of your work is done visually on drawings.

I really enjoy cubify design which is a cheap alternative to solidworks. I have designed a ton of stuff with it.

They both have their virtues. I use both for designing my 3d models depending on what I need. I think being experienced in both will make you better on each piece of software.

Just started learning 3D printing. Highly recommend https://www.tinkercad.com/ for basic playing around. It's limited, and I'll probably need to start using other things soon, but until then it's been a blast to use and learn the basics with.

This older one is pretty neat, too. I've owned it for a while and still can't really figure it out--the shadow mask is incredibly thin, and as far as I can tell it works on magic. http://www.digitalsundial.com/product.html

Here is the patent for that product. Perhaps this will shed some light on how it works. I'll see myself out. http://www.google.com/patents/US5590093

Very cool!

Also apparently a 'digital' sundial was patented at one point - https://en.wikipedia.org/wiki/Digital_sundial

http://www.hineslab.com/digital-sundial/ - The notebook drawings are cool

So would OP be the 'fractal sundial'?

I would consider it a holographic sundial.

A fractal is "any of various extremely irregular curves or shapes for which any suitably chosen part is similar in shape to a given larger or smaller part when magnified or reduced to the same size"[0].

A hologram is "a three-dimensional image reproduced from a pattern of interference produced by a split coherent beam of radiation"[1].

The 3rd dimensional component of the hologram is modulated by the position of the sun instead of the observer.

[0] http://www.merriam-webster.com/dictionary/fractal

[1] http://www.merriam-webster.com/dictionary/hologram

Yeah I think it would be

There's a high profile public digital sundial in Paris, installed in 1989:


Unsure this is still there, Les Halles has been under major works for the last 4 years - haven't seen the sun dial for years.

I doubts the claim about only being able to produce with a 3d printer. I can imagine easily making the layers in mass out of wood and sliding them through bandsaws to mass produce these.

That sounds orders of magnitude more difficult. You might as well 5-axis machine them.

You don't need 5 axes to machine what he machined. It looks like you can do it with 3 (at least, my CNC seems to think it will do it). 4 at the worst if you want to spin it for some reason.

Truthfully, the problem they have is that it's still cheaper, easier, and more accurate to do this with a subtractive CNC machine.

Plus you aren't material limited.

This can't be done in a single setup on a 3-axis, its not xy-monotonic (there are overhangs). Theoretically you could do it on a 3 axis by manually remounting the piece at different angles, but it would be hundreds if not thousands of setups. 4 axis is definitely the practical minimum to machine it.

It looked like the the overhangs can be machined with a small rabbeting bit (remember that we can use more than just end mills :P), and like i said, both my pieces of HSM software seemed to think it wasn't trouble (IE the simulated finished piece is within 0.001).

You are right that in practice, you would likely want a 4th axis rather than messing around, but a 4 axis setup is just not a big deal (the 4th axis on my woodworking CNC cost < 4k)

You could not make it with a 3-axis CNC machine in one piece, but you could modify the design to make it possible without too much trouble. One way could be to make the base separately, and then insert the "blinds" that makes the digits separately.

If you think it's hard, you've never seen how intricate woodworking is mass produced.

This kind of creativity is really something special to the 21st century; not just that people can make things but that they can make things which are so complex and otherwise would have been cost prohibitive before CNC technologies like 3d printing.

You're serious? There are a few centuries of history in amazing timekeeping engineering -- long before, guffaw, CNC. Just a random link to a Breguet, for instance:



I am wondering how much extra time it will take for 3D printing as we add support for 10 minute time interval, 1 minute interval and then seconds (extra set of digits HH:MM:SS).

Also will it be practically possible to have second-level granularity?

The width of the Sun in the sky is wide enough that it takes about 1 minute and ten seconds to cross its own diameter. So optically speaking, it would be pretty much impossible to have any resolution finer than a minute, no matter how small the holes are.

I cannot see how to do it, but one way to beat that limit might be the use of diffraction gratings. It might be possible to have the light from two opposing edges of the solar disk interfere and produce a darker spot, thus allowing one to draw the time in darker text on a light background.

If that can work, I guess both the design (I can't see how to design one object that shows a number for say 5 seconds; now fit thousands in a single object) and the engineering challenge would be quite a bit higher (at submicrometer scales), and that the resulting contrast of the display would be a lot lower.

Sun isn't a coherent light source, so no interference of light from different sides..

I think it should still be possible, but it will depend a lot on the length of the holes too.

If you imagine a really long tube, any light entering at an angle will eventually hit the side, and if the sides do not reflect any light, nothing will come through the tube.

I don't want to bother doing the math to figure out how big the diameter of the sundial would have to be to have sub-minute accuracy, but I think it is very possible.

skykooler's point is that the Sun is not a point source. I think you may be mentally modeling it as a point source. A point source would make it just a matter of length, but when it's not a point source you can't help but get overlap between two "points" that are close enough together, because they both will be lit up at the same time, no matter how long the tube may be.

Ah, I think you're right.

Though the intensity would fade as the sun moves, so maybe you could potentially have some sort of intensity filter?

Perhaps a nighttime version intended to work with starlight would work. It could be aimed at Polaris and combine the light from all the stars swirling around it to project the digits.

I wonder of you could do some kind of mechanism so that when the leading edge of the sun turns on a pixel, that also warms up something causing expansion which is used to block an earlier pixel that is still on and you want to turn off?

That might not count as a sundial, though.

The change in the direction of light per second will be way too little to create a digital sun dial of this style. It would need some sensors to detect it which kind of defeats the purpose again. It's not a shortcoming of 3D printing but of optics/physics

Consider the size of the sun: it's not a point source. Even if it was, the "seeing" (astronomical term for sharpness of objects in the sky) is usually on the order of arcseconds at night, probably much more (due to convection) during the day. So even with image-forming optics, 1 sec temporal resolution is very tricky. (earth turns 15 arcseconds in one second)

Yeah, not to mention the simple problem of diffraction you get when light encounters obstacles such as narrow slits.

You'll only get diffraction when the slits are comparable to the wavelength of the light, i.e., on the order of a micron. I believe you can see light peeking out through a micron slit if you're looking directly at it in a dark room, but I don't think it's feasible to see diffraction in shadows. The fuzziness you see in normal shadows comes from the finite angular size of the light source, not the wave nature of light.

A related question: could you make the sundial work for a longer period during the day? Is a 24-hour sundial at all possible?

In most places 24 hours wouldn't be possible, because even if you were somewhere with 24 hour sunlight, for part of the day the shadow would not be cast on the earth. You need to angle the sundial so that it's perpendicular to the sun's path through the sky, so for at least a portion of the cycle the sun would be 'below' the sundial, casting a shadow upwards. I suppose if you were very close to a pole near the summer solstice it could work though.

I loved this. Then I thought how about if you could use words which appear in the shadow over the day.

As ever someone had already had the same idea written the code to produce the OpenSCAD files for different wordings and put it on Github:


Cool! Perhaps someone could cast a piece like this with concrete or baked clay inside a larger, sturdy building to display an alphanumeric message to future generations, only during specific alignments. I can see one potential benefit compared to hieroglyphs, tablets, pillars[0], and other megalithic messages that some of our ancestors left us; it would take different skills to warp its message than simply a chisel or spray paint. One fictional story that comes to mind, Indiana Jones' Staff of Ra[1], makes this seem like even if only for a treasure hunt game, it would make for a fun story later on.

0: https://en.wikipedia.org/wiki/Ashoka_Pillars

1: http://indianajones.wikia.com/wiki/Headpiece_to_the_Staff_of...

It should display the time with Roman Numerals... then ancient Romans could use it.

This is very cool, I'm going to have to play with OpenSCAD.

This is just incredible, would love to see a version with milliseconds support:) It'd also be nice if the numbers didn't fade in/out but had a sharp cut off point where they'd quickly switch.

While theoretically possible, it'll be very difficult to realize physically. If you allow fractal constructions, purely unrectifiable sets can fit the bill. For example, here's an example in 2-dimensional space that casts a solid shadow when the light source is along one axis but not from any other: https://books.google.com/books?id=usjNBQAAQBAJ&lpg=PP1&dq=&p...

With millisecond precision I think it's even theoretically impossible as the slits would become so small it destroys the shadow in an effect seen in the double slit experiment.

But that's just a gut feeling.

You'll have to make 500 meters thick clock, but theoretically it's possible.

And practically, too, perhaps not politically or economically possible.

Think about how it works and you'll realise why those are incredibly difficult to achieve.

Are you planning on having a javascript sundial? :)

Something like this came up on hn a while back: https://news.ycombinator.com/item?id=8042673

Very clever! Is there any reason why you couldn't just carve out tunnels shaped like the numbers, using a stencil typeface?

You'd need a lot more carvings.

How does the error vary with how far you are from the edge of the time zone?

There shouldn't be any error, because you can rotate the top piece to calibrate the time. He also mentions in the video that because of that you can account for daylight savings time changes.

As much as local solar time differs from your time zone. This would be of limited use in China, for instance, where the entire country is on a single timezone, despite solar time having a four and a bit hour spread.

It would be relatively easy to modify the script for your own location in China to display the correct time. So that it is not displaying 12:00 when the sun is directly overhead.

Wow. This is amazing!

finally a killer app for 3d printing. Future is here.

so this proves that time really exists ;)

If you see that when it casts these shadows, then you could call it real, sure. You could also look at it as celestial bodies aligning and their patterns of shades of light.

Accuracy helps a lot when using understanding of some things' existence to find another thing and its attributes (incomplete understatement). Proof making and checking helps a lot for someone to stay true to their beliefs and maintain a consistently accurate path.

Seems cool. But a 15-minute video? Pictures or it didn't happen.

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