Guiding ships with Moire patterns

I was inspired by Tom Scott’s excellent video and links here  

where he talks about a particular type of “Inogon” light used to guide ships through channels or harbours.

The patent is here: and the military report on the effectiveness is here:

(Hint; They don’t seem to like it much).

I decided to build my own to play around with the effect. After a few minutes sketching in inkscape and a few more lasercutting,  I had this:

cut pieces v01.JPG

I followed the claims in the patent fairly closely. They advocate between 1.5 to 1.8 ratio of pitch spacing to the width of the dark bands, and I used 1.65 (this yields a mask with a ‘duty cycle’ of around 40%), and to use only a single excess band on the first mask relative to the second.

Here’s what it looks like when illuminated from the back, and dead-on to the beam:


(There’s some minor circular effects because the separation of the two grids is significant compared to how close I’m standing. If this was on a riverbank and I was 100m away, that’d disappear)

Here’s what it looks like from various angles:

compilation v01.png

Am I happy with it? You betcha. It does exactly what it says on the tin. It’s a intuitive and nifty way to guide a vehicle, requires very little ‘calibration’, and can cope with a dozen or more people using it at the same time without any problems.

Do I think it’s the clear best solution to the problem? Sadly no.

Typically a harbour doesn’t have one razor-thin path of traversable water. Instead there’s a clear pathway that you shouldn’t stray too far away from. The Moire system will give steering advice even if you’re in a safe area, but slightly off the main ‘beam’.

I remember a few years ago in Newcastle seeing a much simpler and elegant system using 3 lights like below. (Excuse the mess, I grabbed whatever I could find nearby so I could compare the two approaches at around the same scale).

sketch v01.jpeg

If the top lamp is between the lower two, then you’re on a safe course. If it’s above one, then you’re on the edge of the safe area, and if it’s outside both, then you’re off the path and need to steer back straight away.

3 light sketch v01.jpeg

In a real situation when you’re manoeuvring a ship there are other factors to think of, such as cross-currents, weather, or other ships to avoid. Having to stick to a narrow platonically perfect course has a non-zero cost in terms of extra fuel used, demanding increased concentration, higher risk of accidents as everyone is trying to use the same line, etc.

If I were a pilot I think I’d much prefer a system like the 3 lamp, that lets me know when I’m actually in danger, rather than a system letting me know I’ve deviated from a line someone drew on a map.

However,  it’s a super cool bit of design and maths, and I do think the system is useful when the object you want to mark is actually narrow. In the youtube video it was marking a submarine cable, so people didn’t drop anchor and foul on it. That seems like the perfect use for the Moire pattern.

Files are here for anyone that’s interested in making their own:



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Boxmaking jig – the “cladding ruler”

I often find myself making wooden boxes for projects, and my favourite way is with plywood and batons, glued and nailgunned together. I usually make the left and right box sides with batons reinforcing, then the top, bottom, front and back are just flat pieces of wood. Once the two sides are made, you can glue the rest of the box together by hand on the table, without any need for clamps or alignment stuff:

overview pic copy.JPG

One side panel of the box, batons glued to plywood

It’s brilliant for prototyping, since the nails are your ‘clamps’ while the glue is drying, and you can keep working on the box rather than having to put it aside for hours. Once the glue is dried, the boxes are rock solid.

(I first saw Adam Savage use this method on youtube, and I immediately went to the hardware store to buy a nail gun…).

One tricky thing with making a box like this, though, is holding the batons in place exactly a wall thickness from each edge. Clamping and keeping it aligned it is difficult, and I don’t like to nail the wood while it’s anything other than flat and level on the table.

Here’s my solution. The “Cladding ruler”:

overview pic.JPG

It’s made of four layers lasercut. The first three are glued, and the last is loose. I use M3 nuts and screws to loosely hold it in place:

grip closeup.JPG

The baton has glue applied, and is inserted. The plywood can now be flipped over and nailgunned to hold it in place:

while gluing.JPG

You can also use the jigs to put in the long sides of the panel:

long edge gluing.JPG

Ready to be flipped and the long side nailed in place

After gluing and nailing the left and right panels, and the rest of the box is ready to be assembled. It’s a super quick, after cutting the wood I had the box together in about half an hour, and even though the glue isn’t dry yet, the whole things is robust enough for me to keep working on cutouts and other stuff straight away.

finished box.JPG


Files here for anyone that wants to make their own:


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My globe now featured on Tested

I’m pleased as punch that my project was picked up by the youtube channel Tested. Norm and Sean lasercut my Dymaxion globe here:

I’m also glad they noticed a few of the features I spent time on (such as reusing the verticies, scaling the holes, making the full set of platonic solids, etc). I usually try quite hard to make designs scalable and useful for others to make without much effort, and it’s nice when those things are appreciated.


Also I should point out that a few modified version of the design now exist on thingiverse. I’d suggest using one of them rather than my original files, as I was never happy with the engraving, and these new versions make it easy:


From KBST:

From PandaCNC:

From Concretebox:



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How Big is the Universe – Exploring the Hubble Ultra-Deep Field

This is a way to visualise the size of the universe, and in particular how much of the sky the amazing ‘Hubble Ultra Deep Field’ picture takes up.


One of the most majestic images humanity has ever seen.  I stole this copy from Wikipedia:

The Ultra Deep Field is 2.4 arc-minutes wide (0.04 degrees), so it’s a tiny slice of the visible universe. In fact you’d need thirteen million exposures just like it to cover the entire sky.

But, even in that tiny sample you there are over 5,000 galaxies. (I’m not even going to get into how many stars can make up a typical galaxy, but ours contains about 200 billion stars)

But what does that actually look like? I decided to make something to help visualize just how small a slice of sky the picture is:

single board copy 2.jpg

Here’s how you use it. The string is 5 meters long, and you hold the small piece next to your head, and look at the tiny 3.5mm square target.

Using the board 04c.png


I’m super happy with how it turned out, it’s a very immediate way of understanding the true scale of the image.

I got the HUDF image glossy printed at officeworks, for about a dollar a sheet, and lasercut a few boards at the same time. finished boards.jpg

Files up here for anyone that wants to make their own:

I’m happy to give away my spares to any teacher or educator that’d find them useful. If you’re interested, shoot me an email.



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Lasercut Contact Goniometer for Crystallography

Just a quick one this time. Here’s a simple lasercut design for a ‘contact goniometer‘ which is used for measuring the angles between two faces of a crystal.


lasercut goniometer.jpg

It’s lasercut from 3mm acrylic, and to make the engraved text stand out, I rubbed green acrylic paint on the surface, then wiped it off before it dried. The paint stays in the engraved sections and highlights them nicely.

By holding the edges against the crystal face, both the direct and internal angle can be read out. I was originally only going to include one scale, then I realised various people use different conventions.

lasercut goniometer 02.jpg

The object I’m measuring in the photos is the excellent 3d printed quartz crystal by Pmoews here.

Files up on thingiverse for anyone that wants to make their own.



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CPK Molecular Models with Polymer Clay

I’ve been getting into molecular modelling recently, and I wanted to experiment with different ways of making my own models cheaply and easily. I liked the colour scheme and layout of the CPK modelling made by Linus Pauling and others, but their models are fairly chunky, so I decided to go with half the scale they used (1 Angstrom now being 6.25mm)

This was my first idea, a 6mm deep template to mark out the right volume of clay for each atom type: thumb_IMG_2868_1024.jpg

Once you have the right amount of clay, a heavily scientific process known as ‘smushing’ is used to turn it into a sphere:


A perfect 1.7 Angstrom radius carbon atom. 

While that worked, it wasn’t terribly quick. After playing around a bit, I redesigned it to allow multiple atoms to be cut out at once. Also, the edges of the jig are used to support a rolling pin exactly 6mm from the surface, so the volume is nicely repeatable.


How you split an atom. 

Also note the different coloured markings on the edges, allowing you to divide up the clay for different atom sizes. I simplified it a bit down to only four sizes, since I figured people won’t be able to tell the different between a sphere of radius 1.52A and 1.55A just by holding it in their hand.

Once the atoms are divvied up, you can even put in some rare earth magnets to make a suitably geeky fridge magnet:


Astute readers will note that the clay making up these atoms, is actually made of atoms also, which I maintain makes this a fractal. 

You should really use a better work surface than MDF too, my clay got all grubby because I didn’t think to prepare something cleaner. A glass countertop is perfect to work on and easy to clean afterwards.

Then just bake the clay as normal in the oven:


Being cooked. Does that make this a reactor? 

Rather than my home oven which I’ve used previously, I used a turbo oven so I could bake them at the R+D space. Turns out the turbo oven I used either isn’t perfect for polymer clay, or I need to work on getting the airflow managed better. The models I made broke apart, but were easily superglued back together. I’m not concerned, the main thing I wanted to get sorted was the cutting jig, and I’m extremely happy with how that turned out.

While mushing clay atoms together isn’t going to give the world’s most precise atomic angles, it’s certainly capable of capturing the feel of a various compound, and I’d suggest it’s a good way to aid learning.

Files up here for anyone that wants to make their own:

And if you do make your own model, please let me know and I’d love to see a pic!


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Lego Crystallography

I’ve been reading up on crystallography recently for an upcoming project, and I was having a hard time wrapping my head around Miller indices. I kinda got it, but I wanted something tangible to work with, darn it.

I started making 3D models in CAD, and also cutting up pieces of wood to glue together, when I realised that I already had a prototyping system in my living room that would be perfect for the job.


Lego. Is any engineer’s bookcase really complete without it? 

It’s perfect for displaying the various crystal faces.


Lego with a Miller Index of (1,0,1)

And you can see how the ratios of unit cells in X,Y,Z lead to different angles on the face:

thumb_IMG_2977_1024.jpg  thumb_IMG_2978_1024.jpg

Playing around with these models gives one an extremely clear demonstration of the reason behind Steno’s Law (That angles between corresponding faces on crystals are equal for all crystals of the same material). In this metaphor “same material” translates to “same size unit cell” same size lego brick.

And of course the standard 100, 010, and 001 faces. In this case they’re at right angles to each other, but that’s only because the (lego) unit cell is orthogonal. It’s perfectly possible to find crystals where 100 and 010 faces are at angles other than 90 degrees. thumb_IMG_2979_1024.jpg

So, I’m now happy I understand the basics of the Miller Indices, but much like Mary Poppins, lego can’t stay still in one place forever. I decided to make a more permanent set of faces to have on hand so I could free up my lego again.

Here’s some I made from balsa bricks:


The unit cell here is anything but cubic, which I’m actually quite pleased with. It shows how crystals aren’t just a collection of perfect platonic solids. 

And a few years ago I did a large bulk purchase of cedar cubes and spheres (I had a rough idea of making a marble computer), and I decided to put them to good use: thumb_IMG_2984_1024.jpgthumb_IMG_2983_1024.jpg

I attempted to try and cram in the most informative faces for a fixed number of cubes by fitting in the (0,~2,1) and (0,1,1) face as well.


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Turn Binomials into Gaussians with Polymer Clay

I’ve been playing a bit further with the visual demonstrations of the binomial/ central limit theorems. I love polymer clay as a medium, it’s extremely easy to work with, colourful, and you can even make fractal patterns with it.

Here’s my first approach, it turned out a bit less intuitive than I was hoping, but it was still fun to make.

The first step was to make a series of square stacks, encoding all possible 3-bit values (000, 001, 010…… 111):




Then slice them in quarters and make long strands from each:


Turn each one into a long rope:


And assemble into a Galton board style device, with each path represented by the colour ordering of the strand (e.g. 010 = Left, Right, Left)


You can immediately see that at the final clusters at the bottom, the number of each colour bands is the same (e.g. three blues, two blues and an orange, etc).

Representing that in the Galton board left-left-right leads to the same result as right-left-left.

I was fairly happy with that, but I wanted a more detailed model, and I decided to drop the encoded-strings idea as being to difficult to implement without distorting. Here’s my results for simple strings:


This I’m pretty happy with. You can see at a glance why the middle result is 6x more probable than the right hand result (since six paths lead there versus only one), and you also don’t have to wait for the balls to collect as with the conventional display.

After baking the models in the oven for half an hour they’re now robust and permanant, and I’ll keep them on the shelf for the next time the central limit theorem comes up.

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Braided Galton Boards – Visualizing Probabilities with String

I’ve been playing around with Galton Boards recently. They’re an awesome demonstration of the central limit theorem, and how several independent 50/50 events sum together to make a Gaussian/Bell curve.

Seeing the standard Galton board gives an intuitive feel for how random variables behave, but it takes time to run the experiment and see the results accumulate.

I wanted a more immediate visual demonstration, and after a few prototypes I settled on using a thread to represent each possible path through the system:


I used 12.5mm dowels cut to size, and hammered into the lasercut wood.


The 64 and 32 string versions

The strings are cut to length, then held in place with a screw clamp and threaded through one at a time:


Stats and craft therapy all in one

It might be because I finished this late at night, but I found it very difficult to thread without making a mistake. The strategy I ended up using was to hold the previous thread in my left hand and the next thread in my right. By jiggling my left hand I saw the old thread bounce, which gave a good reminder of where I was in the sequence, and hence to put the new thread in the right spot.


Files here for anyone that wants to make their own:

It took a bit of prototyping before I got a form factor I was happy with. Here’s two of the failed attempts, that I avoided because they either weren’t practical, or they were slightly too opaque a display of the concept:


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Lasercut Yarn Bobbins

I’m working on a project that involves lots of different coloured cords, and I wanted a way to avoid tangles while transporting & working with them.


Files here:


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