Mechanical GIFs Featured on Cool Tools Gift Guide!

My acrylic models were just featured at the top of the list on the CoolTools Holiday Kits gift list! Which is a bit of stress since I’m scheduled to leave for China early tomorrow morning. Orders were strong today, but we’d built up a good amount of stock already, and are scrambling tonight to make enough to last, hopefully, until I get back.

They are right, of course, these kits are indeed the finest available stylized clear acrylic mechanical models. Chances are you need several, right?

I Just Saw the Coolest Thing!

I just saw the coolest thing ever: a Wall Printer!

It's really nothing more than a 4-color inkjet printer on its side, pointed at a wall instead of a piece of paper. The head goes up and down, and because moving walls is hard, the beam holding the head moves slowly along the horizontal track set up to hold it.

It's clearly modular so you can set up as much track as you like by joining sections. The drive motor for moving the beam is mounted in the self-contained vertical unit: it turns a gear engaged with a toothed belt that is stretched the whole length of the horizontal track. Loops of extra belt at the end indicate that this is not the maximum length. Really, there shouldn't be any practical upper limit to how long a wall you could paint with this thing.

A laser cross-hairs lets you position it just right:

Apparently I wasn't the only person who thought this was a pretty rad invention:

After the spectacle we had fire shrimp:

And after the fire shrimp we went back to see the finished wall:

The guy said it can print about three square meters per hour, so apparently he'd been at this for a while:

The resolution is not super high, but for a billboard-sized image, it's perfectly servicable.

It did show some bleeding or over-spray in some places but not others.

All in all I think it did a great job under difficult circumstances. It appears to run autonomously from a built-in battery (no cords), and the image is presumably on the memory stick you can see inserted on the front of the print head. So it should be possible to set it up anywhere in the middle of nothing and paint a wall. Imagine the possibilities for slow-motion urban graffiti!

According to this TaoBao (Chinese eBay/Amazon-like market) link, this lovely, lovely device costs about $2700, which seems like a very reasonable price to me. 

Public Appearances in Beijing, July 19-22

I wil be giving five (!) public talks in a row at the Beijing Science Festival over the weekend of July 19-22. Although I will give five talks, there are only two different talks: one talk (three times) on Chemistry/Elements/Molecules/Reactions, and one talk (two times) on my new "Things" book project. This link gives details about the festival (in Chinese):

I don't exactly see where it lists the times of my talks, but they are:

           July 19 at 14:00
           July 20 at 11:00 and 14:00
           July 21 at 14:00
           July 22 at 11:00

Phew, I'm tired already! As for the location, well, hopefully if you're in China and want to go to these talks your Chinese is better than mine and you'll be able to navigate the site to figure it out. All I could get out of Google translate is "This uncle is really interesting." which I think is referring to me.


A few years ago I thought I had hit the pinnacle of my career as a writer when a kid came up to me just before a book tour talk and showed me a picture of his cat, which he had named Theo after me. What could possibly top that?

Well, I just found out! Behold, here is Liam, a third-grader, dressed up as me, complete with painted on beard! For a school project he was supposed top pick a favorite author, write a biography, and dress up as his chosen person. He chose me! How cool is that! Sadly two important details of his portrayal are now out of date: I don't have a beard anymore (new girlfriend) and I don't have any hair on top either (old age?).

Thank you Liam for making my day.

I Made a Clock!

I made a clock today and I'm so happy it actually works! It runs upwards of 20 minutes before you have to rewind it, and is currently running at about 58 seconds per minute. Baby steps, ok, baby steps.

The image above is the CAD file showing the frame (back and front), gear train, dial faces, and the all-important escapement (on the left).  We haven't done any proper photography of it yet, but watch this video to see how it works, fastened to a shelf in my laser cutting bunker:

As you can see, this is a very spread-out clock. The gear chain is laid out in a line: second-hand on the left, minute-hand in the middle, and hour-hand on the right, with each hand having its own dial face. I did that so you can see the gear chain that reduces the speed by factors of 60 and 12 respectively between the second, minute, and hour hands. Analog clocks with hands, even ones that run on a battery, are all about this gear chain. In a normal clock they fold it in on itself so that all three hands end up in the same place, on a single dial face. That's great for being a useful, compact clock, but terrible for seeing how the gears work. 

A crucial part of every purely mechanical clock is the escapement. This is the part of the clock that translates the swinging motion of the pendulum into rotation at a precisely measured rate, and at the same time imparts tiny bits of energy to the pendulum on each tick, in order to keep it swinging.

There have been many designs of escapement over the 700-odd years since the first "verge" escapements were developed in the late 1200s. My clock uses a version of the "anchor" escapement, the second type to come into common use (in 1657). There are newer, better designs, but they are less tolerant of mechanical imprecision. Clocks, and escapements in particular, are dependent on very high precision machining, so much so that it's fair to say that the entire field of precision metal working advanced for several centuries mainly to make better clocks. While I love my laser cutter and consider it to be a very precise tool, by the standards of clock making it is horribly crude. Good clock parts have errors measured in thousandths or ten-thousandths of a millimeter, so my laser cutter's tenth of a millimeter precision is pretty bad. 

But, it's good enough to make this fully functional escapement, and that's what matters to me. (These, by the way, are the escapements that didn't work.) It took about a dozen tries before I got the dimensions just right so it would reliably advance, and also send enough energy to the pendulum. 

Another crucial thing about a good clock is how friction-free it is made. The less friction, the longer it can run before it needs to be rewound (either by re-coiling a main spring, or by lifting up weights whose slow dropping provides energy). To achieve low friction, all kinds of tricks are used, including extra-fancy oil and even "jewel" bearings made, typically, of sapphire. I have one "anniversary" clock that runs for an entire year without being rewound!

By contrast, my laser cut acrylic clock runs for about 20 minutes before the weight (shown here) hits the floor. The weight is a hollow acrylic octagon, and if I make this available as a kit I will suggest that people fill it with whatever heavy things they have handy, like pennies for example. I filled it with #6 hex nuts, because I have a lot of them. The weight falls fairly fast because it's connected at a point in the gear chain fairly close to the escapement, where the gears are turning relatively fast. If I connect it later on, where it would turn much more slowly and thus last much longer, there is too much friction and too much gear reduction, causing too little energy to reach the pendulum, causing the clock to stop.

The pendulum bob, shown here, is the same design as the weight. Here's an interesting fact I learned in trying to decide how long the pendulum needed to be for it to tick at the correct rate. (The period of a pendulum is directly proportional to its length.) It turns out that a pendulum with a period of two seconds (which will tick once every second, since the escapement advances once every half-cycle of the pendulum) has a length very close to one meter. Why? Because that was the original idea for how a meter should be defined: one meter was proposed to be the length of a pendulum with a half-period of one second.

This did not end up being used as the definition, at least not officially. Instead they went with "a meter is 1/10,000,000 of the distance from the earth's equator to the pole", which is a completely ridiculous basis for a unit of length. It's always bothered me how utterly arbitrary and useless this definition is, especially since that distance was not actually known with any great precision at the time. It's always sounded to me like a post-hoc justification for a length they'd already settled on for some other reason. (Like, for example, that it's about the same length as the English Yard, but that couldn't be it because the French hate the English.)

Now it all makes sense: it was a post-hoc justification. The length of a one-second pendulum is a much better basis for a unit. It's something that could be reproduced by anyone, anywhere who is able to determine time accurately (which you can do from the sun, for example). But no, they went with the silly equator-to-pole distance. I'm assuming politics was involved. (Since no one could actually use the equator-to-pole distance, they had to make a "prototype" meter, a platinum-iridium bar kept in Paris for many years until the definition was updated to be in terms of wavelengths of a certain frequency of light, and then later in terms of the distance traveled by light in a specified time.)

Well anyway, at this point I have one copy of this clock, and I'm going to make a second one that will put together with gloves on, in order to photograph it for my book. I might also make it into a kit for sale at, if it seems like something people would like. Comment if you want to lobby for it being available....

I Made a New Engine!

I'm was at the G4G conference last week and working on my (6-minute) talk caused me to think again about the motivation behind making steam engine models. 

Nearly all model steam engines (and some full-size ones) use a beautiful set of harmonic motions to create the self-sustaining, alternating application of steam pressure to first one side and then the other of a piston, which drives a flywheel, which in turn drives a valve that causes the alternating steam pressure.

This model shows the fundamental fact that the two harmonic motions, that of the piston and that of the valve, are 90 degrees out of phase. When the piston comes to rest, the valve is moving fastest to switch the steam over to the other side.

This is a beautifully simple mechanism, and it's the smoothest possible way of running an engine: everything is in harmonic motion, meaning the least possible change in acceleration at every point in the cycle.

But, it requires two connection points to the flywheel, which seems like something that could be subject to further simplification. If you could make a mechanical differentiator to take the derivative of the sine wave motion of the piston, you could use that to synthesize the cosine motion of the valve. But that's not possible in any pure way, because you would necessarily require infinite leverage or something to that effect. (Because the valve needs to be moving at maximum speed when the piston is stationary: how do you derive motion from lack of motion?)

But it turns out there is a simple and commonly-used (on real steam engines and some models) way to achieve a sort of approximation to the cosine wave. And the curve you get is actually better than a cosine, in that it makes the valve move faster exactly when needed, and remain completely stationary when it doesn't need to move. The motion is not smooth, but it serves the engine better. Notice that this design has only one takeoff, yet the motion of the valve is still maximized at the point where the piston comes to rest (actually just before).

The trick is to use the very top/bottom of the sine wave, magnify it (with mechanical leverage), and then min/max it (with a sliding toggle) to create hysteresis. Mathematically, the motion of the toggle is approximately 5 * max(0, sin(x) - 0.8), with appropriate switching of the sign for the negative lobe of the sine wave. This plot shows the piston (green) and valve (orange) positions as a function of time through one complete cycle.

If you add a cosine wave to the plot (actually -cos(x)), you can see how the jerky, toggle-based curve is a mechanical approximation of a cosine, but squared off. What you actually want from the point of view of steam flow, is a square wave: the valve should switch instantly from one side to the other, exactly at the extremes of motion of the piston.

The whole elegance of having two pure harmonic motions is really not ideal at all from this point of view, which is why such mechanisms are not used on large engines.

There is another "mathematical" way of looking at the difference between engines that have separate sine and cosine connections to the flywheel, vs. a single sine wave connection. The combination of a sine and cosine wave define a direction of time, as it were. With time (x-axis) moving forwards to the right, the sine wave leads the cosine wave. If you reverse time, the cosine leads the sine. Therefore, this engine can only run in one direction (unless you interchange where the steam is coming in with the exhaust).

But a single sine wave does not change if you reverse time: it is symmetrical to time reversal, as they say in physics. That means, necessarily, that the single-connection engine above must be able to run in either direction without changing anything in the mechanism. Another way of looking at it is to say that the entire mechanism to the right of the flywheel has no way of knowing which direction the flywheel is turning. The harmonic, sine wave motion will be identical regardless of the direction of rotation, therefore it must work either way. So what determines which direction it actually goes? It's all down to which side the valve was flipped to when the engine is started up. The hysteresis of the valve creates the direction-of-time difference.

That's actually a thing in real engines: I saw a model steam engine with this type of valve just a few days before making this design. The guy showed me how you flip a lever before starting the engine, and it was clear that this lever was not redirecting steam. At the time I didn't understand how this could work, which caused me to worry about it until I finished this model, and now it all makes sense.

Literally hundreds of patents were issued over a span of centuries, focused on improved methods of controlling the timing of steam engine valves. For example, you might want to optimize for maximum work per unit of water used to create steam, instead of optimizing for maximum power from a given size of piston,. If so, you design the valves to admit a small amount of high-pressure steam at the start of the cycle, then close off quickly, allowing the steam to expand within the cylinder. The pressure drops off as the cylinder moves over, but you don't use any more steam. In practice this is said to get you about 2/3 of the work for 1/3 of the water, compared to applying full steam pressure for the whole stroke.

Towards the end, before the steam engine was replaced completely by internal combustion and turbine engines, the valves were mostly "poppet" style valves, driven by cams. The timing could be changed at will to optimize for torque or efficiency.


P.S. I love my laser cutter! As I said, I came up with this design while working on a talk. That was Monday evening, and my flight out to the conference was Wednesday early morning. Around 11PM that night I decided it was nuts to try to actually make the engine in time to take to the conference, so I started working on the CAD files. By around 1AM Tuesday morning I had a design ready (based on my Folded Steam Engine, lengthened a bit and with the valve connection replaced with the new design). Around 10AM Tuesday morning I went to the shop and laser cut the new design. It took four or five re-cuttings of the piston and toggle lever to fine-tune the dimensions so the valve moves the correct distance (taking into account the reality of the laser cut width and the slop in the screw pivot joint, which are a bit hard to predict in the drawing).

Once the design was good, I made six copies, put a couple of them together, then Nick and I photographed a time lapse of the new design. All that took maybe 2-3 hours.

I really do not know of any tool that works so fast and so perfectly to churn out beautiful-looking mechanical parts. I really wish 3D printers could come anywhere near this level of speed, economy, and beauty of results. While waiting for that, I will continue to live in my 2D laser cutter world.

Mechanical GIFs Models Now Available Open Source on Thingiverse

I've finally gotten around to my original intention of publishing the plans (layered DXF files) for all the laser-cut acrylic parts of all the models featured at

You can find them at my Thingiverse collection. I have no idea if anyone will actually try to make them from the plans. I'm pretty sure that, unless you already have all the different parts and types of acrylic on hand, it would be cheaper to buy my kit of the same thing. But on the other hand, it might be more fun to make your own parts? If you're the sort of person who would make this sort of thing from Thingiverse plans, I'd be interested in opinions.

I call it the Bagger 2000

I promise that some day I will write about something other than making kits, but for now that's what I'm all about. Today I'm pleased as punch about my new semi-automatic small parts bagging tool, which I call the Bagger 2000 (because it holds and fills 20 bags at a time, and because 2000 is a hundred times better than 20 as a model number).

The issue is this: we need to fill hundreds of 2" x 4" poly bags with lots of little nuts, bolts, and small plastic parts. Each bag gets a dozen or more different parts, and sometimes a dozen or more of one particular part.

We had been doing this using a batch of 20 pill counters (small trays with a trough on the side, designed for counting out pills in a pharmacy). This works, but it is tedious, and the sides of the trays are very low, meaning there is a constant danger of a part getting knocked out before it's emptied into the bag.

What I wanted was some kind of system where I could drop parts directly into the bags using a funnel, or something like that. But it would have to be 20 funnels, one for each bag in the batch, and I couldn't think of a good idea for how to hold the bag onto the end of the funnel, how to hold up the funnels, and so on. Until I realized that I own a laser cutter and have been practicing my inventing skills.

Here is the result: the Bagger 2000!

Being made entirely of clear acrylic, this object is actually quite difficult to decipher from a photo, so here's a short video that gives a better idea of its three-dimensional structure. There are 20 individual rectangular funnels: at the bottom of each, the acrylic sides have been bent around to form little upwards-pointing hooks.

To use the device, you flip it upside down and load it with 20 poly bags. The acrylic clips grip the zip closure on the poly bags. Flip it back right-side-up and you have twenty bags hanging underneath 20 funnels.

You can drop items directly into the bags. Here I've added the screwdriver and wrench included with most of the kits:

But dropping things straight into the bag is not ideal, because (a) it's very hard to recover if you accidentally drop in too many, and (b) it's hard to double-check that you got the right number, for items where there are multiples. (E.g., did I just drop in 3 or 4 of those tiny screws?)

What's needed is a staging area where items can be laid out in plain sight, before being dropped down into the bag. My big breakthrough on this project was realizing that the semi-automatic parts counter (described in an earlier blog post) was perfect for this job. The funnel array has exactly the same dimensions and spacing as the parts dropper, so when the dropper is placed on top of the funnels, they line up perfectly.

Here is a video showing how an assortment of different lengths of screws (manually counted and placed on the parts dropper) can be inspected before being dropped:

Here's a side view showing how the parts are guided down into the bag.

Basically this is the exact equivalent of a German "inspection toilet", which includes a special staging area to hold your you-know-what before it gets flushed down to the big poly bag at the end of the pipe. (They do this because they think it's important to inspect your you-know-what for any signs of health or diet problems every single time. Yes, this is for real, though becoming less popular over time, as I understand it.)

Where the Bagger 2000 really shines is when it's combined with the parts counting feature of the parts dropper. Here the parts counter, positioned on top of the Bagger, is being loaded with 16 hex nuts for each bag. You just wipe a pile of nuts over the counting plate.

Then, after double-checking that all the holes in the template are filled, you simply pull back the gate and presto-magic, all the nuts are dropped perfectly into their respective bags. 320 nuts (16 times 20) counted and put in bags in about a minute!

When the bags are finished, you just pick them like ripe fruit from the underside of the Bagger:

This machine has at least doubled the speed of filling the average kit bag, and I think it will also contribute to a lower error rate.

I'm just about ready to start wondering how other people solve similar problems. My approach to learning about a new area is often to try to do it myself first, without looking too closely at how other people do it. Then, when I feel like I have a really good handle on what the issues are and where the difficult problems are to be found (i.e. what have I not been able to figure out myself), then I'll do some research. Usually I find out that there are much better solutions, but I feel it's worth doing the messing-around phase first, because that's the only way I can properly appreciate how clever the better solutions are.

Production Update: Making a hundred of something

I'm at the stage now of needing to make about a hundred copies of several of my mechanical gifs kits. There's a balance between spending time making the kits, and spending time making tools to make the making of kits faster. How much automation is right depends on the scale of operation.

We have settled on a system of making 20 copies of each kit at a time, mainly because that's how much table space we've got readily available. (This shows 20 Combination Lock kits nearly ready to be placed in their retail boxes.)

A couple days ago my photographer Nick suggested a simple device to semi-automate one of the problem steps: counting out a dozen or so small items. (For example, twelve #6 hex nuts for each Combination Lock kit, or 42 nuts for the nightmare Transaxle kit.) After some prototypes and design improvements, I've ended up with a device that lets me count and place twenty copies of a given number of items, quite efficiently, and with hopefully a very low error rate.


The first step is setting up 20 pill counting trays and adding the small parts (nuts, bolts, etc, anything that will fit in a 2" x 4" plastic bag). They are always laid out in a 4 x 5 grid, for consistency.



The parts counter is also arranged in a 4x5 grid, so it not only counts each individual group of parts, it also confirms that all 20 trays have gotten their dose of parts. A custom template slid in the top determines how many of what shape of object will be counted out. Here it's seen loaded with six springs in each of the 20 positions, for the Pin-Tumbler Lock kit.

Below we see it in action counting out seven #2 nuts, also for the Pin-Tumbler Lock kit. This is literally Koatie's first time using the new device: we both got much faster at it after a few passes!

Nuts are particularly well-suited for this kind of device, because they fall automatically into the holes in the template. We can fill it just by wiping a bunch of nuts over the top and then pouring off the excess. But the template seems to work well even for things that have to be placed one-by-one into the slots. For example, these pins for the Pin-Tumbler Lock don't fall into place, but it still faster and more reliable to manually place them into the slots, and then dump them out automatically.

If you're curious, here's the first step in the second stage of the assembly process: the larger acrylic pieces. Those are laid out on squares of bubble wrap, after being laser-cut. Here's a 32" x 48" sheet of about half the parts for 68 copies of the Pin-Tumbler Lock:

Well, I hope you're not bored with my endless details about manufacturing. It's a learning process, that's for sure.