The process of locating holes with a CNC machine is copiously supplied with opportunities to totally mess everything up

Okay, here’s what happens:

You’ve got yourself a nifty robotic doodad called a “CNC milling machine” which cuts through hefty chunks of metal like butter… if you don’t mess up. If you do mess up, there are horrible grinding sounds, the smattering of “ping” and “tinkle” sounds as important bits and pieces shatter and fly into the walls (this is why safety glasses were invented), and long gouges in said metal chunks if you’re lucky, and in your nifty robotic metal-carving machine if you’re not.

We’ve learned that about 3:00 a.m. — at the latest — is when we start to make lots of mistakes. The other night we broke three tool bits in the space of ten minutes before it occurred to us that, hey, we were tired! and we were having difficulty concentrating!

Two of these bits were buried the in material we were trying to carve. One bit was embedded in the machine itself. Actually, it was embedded in aluminum plating which we’d placed between the work and the machine, because we just knew we were going to mess up badly at some point, and we wanted to protect the machine from ourselves. How prescient of us!

These ten minutes cost us about $30 in materials and tools, which is not much. It also ruined about eight hours of work, which was painful.

Now, we know that everybody does this when they learn how to use these machines, which is why we’ve been taking precautions to protect our investment, and why we’ve been taking notes to help us study and address the mistakes. Here’s what we’ve learned so far:

  • A nice big friendly red PANIC button must at all times be within arm’s reach. This is known as the “emergency stop” button. The purpose of this button is to make all the moving parts stop moving exactly two milliseconds before the machine eats itself according to your careful directions. The timing is important here: any later, and you’ll leave horrible scars on your work or your milling machine; any earlier, and you won’t almost have a heart attack, which means you simply won’t learn anything from the experience. The almost heart attack is very important.
  • Each degree of freedom of movement provides your milling machine more ways to damage itself. Supposing p_x, p_y, and p_z are the probabilities that the machine will jam in the next ten minutes on the X-, Y-, or Z-axis, respectively; the probability that the machine will jam on at least one axis in the next ten minutes is 1-(1-p_x)*(1-p_y)*(1-p_y). Add more axes to make the problem worse. This is a horribly complicated way of saying that sensors absolutely must be installed to monitor the machine’s movement in each degree of freedom. Otherwise the machine will become lost, and as it no longer knows where its cutting tools are, it will begin to cry and wail and throw an embarrassing tantrum, and then have a meltdown very like a lost child in a department store. And people will stare accusingly at you and your poor machine, and you will feel like a lousy parent.
  • Find a way to automate the measuring of each milling tool’s length immediately after you lock it into the machine’s spindle. Otherwise, when you run out of coffee, and you swap-in a new milling tool, and you tell the machine how long the tool is, you will probably be wrong, and the machine will either carve pretty patterns in the air above your work, or it will try to carve pretty patterns in the table under your work. In the latter case, the machine will happily puncture your work and shatter your milling tool on the way to the table.
  • Find a way to automate the process of precisely locating your workpiece in your machine’s coordinate systems. For pretty much the same reason as above, in order to avoid pretty carvings in the table, punctured workpieces, and shattered tools.
  • Most CNC machine controllers have a single “probe” input. You will probably want to use both a “touch probe” to locate workpieces in machine coordinates, and a “tool touch-off switch” to measure the lengths of your tool bits. Find a way to permanently and concurrently connect both sensors to the single probe input. Otherwise, you will eventually run out of coffee, and you will plug in the wrong sensor. This means that the sensor that should be plugged in will be destroyed in slow motion. If it is the touch probe, it will neatly fold and crumple. If it is the switch, it will be run-through with a sharp tool bit.
  • Take the time to carefully write and test programs to automate as much of your work as possible. If you cannot automate a particular step, if you must perform that step manually, you can at least write code that tells your machine to tell future-you what to do, step by step, when future-you runs out of coffee.
  • Place a protective layer of sacrificial material on machine surfaces which the machine might be able to attack if it decides to eat itself. For example, we bolted an aluminum tooling plate to our milling table, and we consider this tooling plate to be replaceable and disposable, although we hope to not have to replace it any time soon. Sadly, this hope is already dashed, but at least our milling machine isn’t damaged.
  • Finally, when you run out of coffee, stop operating the milling machinery. Even if it isn’t particularly heavy. Ours sits on a little table, and we can easily pick it up and move it to another table, so we can hardly call it heavy. Nevertheless, the good desktop milling machines are capable of many of the same heavy-duty operations performed on much bigger machines that weigh several tons, and which occasionally eat people. So treat your little machine with the same respect you’d give to heavy machinery.

Although none of our machines have tried to eat us, we have experienced the rest of these mishaps. We expect to make many more rookie mistakes as we learn. We try to plan for such mistakes. Taking notes makes this much easier.

Okay, then, back to work…

Good night,



Today’s banner: long curls of aluminum swarf issued from a drilling operation on the lathe.

These were produced by a new 7/16″ drill bit. The drilling operation was quick, the bit requiring very little applied force. In fact, a large increase in force behind the bit results in only a moderate increase in the rate of material removal. This is characteristic of sharp tools, in general — and this is why sharp tools are easy to use.

Dull tools, of course, are characterized by frustration. Using a dull tool is a good way to make the tool duller. And that is why we have a good set of bits that have remained sharp for quite a long time. Of course, we have yet to master the art of sharpening bits. Especially the really tiny ones.

And since our machine work tends toward the small scale, we have a steadily-increasing supply of upside-down bits in our bit-cases (they’re upside to remind us that they’re dull). In our investigation into bit-sharpening methods we’ve encountered opinions held with fanatic conviction:

“A Drill Doctor is the way to go!”

“No, make your own sharpening jig!”

“Sharpening jigs are only good for practicing your sledgehammer technique.”

“When I was a boy we sharpened our bits by hand! Barefoot! In the snow, and uphill both ways!”

“Throw them away, and buy new ones from us! In bulk! Look, they’re shiny!”

“We’ll sharpen them for you. We charge only a modest fee…”

So, anyway, we have a nice wet-grinding wheel. If anyone knows how to use it, please drop us a line.

Best — stochastic.


Today’s banner: a disintegrated Bowden cable, an erstwhile component of the tensioning mechanism in our beloved squiggly-magnetic-dial-indicator stand thingy:

The squiggly-magnetic-dial-indicator stand was, in turn, part of our notatripod, formerly an integral chunk of our makeshift photo studio. This is what the indicator stand looks like now:

On one hand, we are no longer impressed by the design and construction of this device. On the other hand, it is highly likely that we have unknowingly abused the poor thing, and we mourn the loss of our notatripod — it was so very useful. On the third hand, we’re pretty sure we can fix it; but on the fourth hand, we wonder whether it will simply break again.

We seem to have run out of hands while we weren’t looking. (sigh)

Sleep well tonight — stochastic


Today’s banner: a centrifuge, about ten times as tall as the guy standing beside it. (But he’s only three inches high.)

And below is a bucket, with an attractively decorated lid (or at least it looks like a bucket):

It contains a thing. The thing looks electric:

Indeed, the thing has an electrical cord, dials, and what appears to be another thing that perhaps spins:

The bucket fits nicely on top of the electrical thing. It’s a tiny electric washing machine! Its name is “Wonder Washer“, an apparently unbranded Chinese product (not to be confused with “Wonder Wash“, which is a totally different product powered by the human arm).

We like the Wonder Washer because it’s so compact when stored, and it’s highly-portable. It works very well for small items (socks, underwear, washcloths, dishtowels, rags, …). It also works fairly well for T-shirts. It’s pretty much useless for anything more bulky, like sweaters, jeans, towels, or sheets. If you try to use this little washer to wash any of these big items, the little washer makes very sad groaning noises. Also, it’s kind of loud. Not terribly so, but loud enough that you can hear when it finishes washing, even if you’re in the next room. A full load of laundry is 8-10 liters:

A similarly-sized laundry centrifuge, shown below, works well with the tiny washing machine. This spin dryer is made by another company entirely — The Laundry Alternative, Inc (who also make the afore-mentioned human-arm-powered Wonder Wash, which is distinct from the Wonder Washer, whose name-similarity is confusing). This spin dryer is very quiet, and it works extremely well. You’ll still need to line-dry or tumble-dry your clothes after spinning in this device. But we’ve found that if you spin your clean wet clothing in this little centrifuge, and then finish drying on a clothesline or in the tumble dryer, they dry faster than after spin-drying in a standard washing machine.

We’ve photographed a little guy standing next to the spin dryer, in order to give you sense of scale. (But actually he’s only there for the fun of it. The spin dryer is not, in fact, sixty feet tall.):

Best wishes,



Today’s banner: our improvised photo studio, comprising a dinner table, a curtain rod, a desk lamp and two squiggly-headed floor lamps, two rolls of paper, and several tiny figurines cavorting on the equipment. No, no, please try to contain your envy, not everyone can have a setup this snazzy:

The figurines are fun but otherwise serve absolutely no purpose whatsoever, except maybe a kind of conspicuous consumption: “… our photo studio has a troupe of tiny acrobats that perform on the lighting equipment. They’re just for atmosphere. They help keep the mood light.”

Although the studio is improvised, it works so well that we’re keeping it.

Have a good night — stochastic.


Today’s banner: metalworking layout tools, improvised, on a glass surface plate (also improvised).

We recently overheard an engineering student ask a really good question: where does precision come from? The manufacture of nearly every precision instrument derives that precision, ultimately, from something else that’s even more precise. Think about that. Infinite recursion, ad infinitum, ad nauseum… Where does it end? What’s the base case? It must be a platonic ideal. Perhaps it pulls itself out of its own navel or something. A realization of the Omphalos Hypothesis. It must invent itself.

We tripped over to the local engineering college’s library where we found a copy of Foundations of Mechanical Accuracy by Wayne R. Moore, 1970, The Moore Tool Company. The copy we found was forty years old. During the last forty years, exactly twelve people had read it. This made us sad. We determined to make up for this dearth of readers by reading it several times.

We discovered that, in fact, the base case is the perfect plane. In the 1830s James Whitworth gave us a simple (if arduous and tedious) method for establishing as a flat plane of reference the surface plate. Surface plates are made as large as needed, and since precision instruments are used to build really big things — think “naval engineering” — by large we mean large, heavy, and extremely rigid. Okay, they’re not as large as an aircraft carrier, but you could stretch out and take a nap on one. If you don’t mind a really hard mattress.

The best surface plates are made of cast iron, or ceramic, or even glass, and are flat to within a millionth of an inch. From this plane — as perfectly flat as we can make it — from this plane can be derived the straightedge, the square, and the precision ways of lathes and milling machines.

In Whitworth’s process, surface plates are manufactured in triplets. Each surface plate is repeatedly compared to the other two, mutually proving each other, their surfaces gradually refined by hand, using a scraper, until no imperfections can be detected. How are imperfections found? One way is to paint one surface with a pigment. Try to mate the surfaces of two plates: on the dry surface, any high spots get inked, and any low spots stay dry. When the pigment is uniformly transferred from the wet to the dry surface, we’ve reached the limit of our ability to detect imperfections.

But why make three at a time? It’s a matter of practicality. Surface plates are usually rectangular, so the only easy rotation is 180 degrees. Now image placing a horse’s saddle upside-down atop another saddle. (I know this seems like a totally unrelated tangent, but bear with me.) If the upside-down saddle is rotated ninety degrees, the two saddles will mate well, even though they’re not at all flat. Now rotate that upside-down saddle by 180 degrees. They still mate.

If you do this with a pair of rectangular surface plates with mirrored but matching saddle-shaped deformations, they will appear to mate well. Now suppose the third plate also has a mirrored deformation that mates well with the first plate. Well, it mirrors the first plate, but not the second. The second and third plates won’t mate. So three plates will detect this kind of deformation, allowing the maker to correct the problem.

These days you can’t get much flatter than a good pane of glass. Through an entirely different process, the Pilkington process, so-called “float glass” derives its flatness from gravity. It’s really cool (or rather, very hot): molten glass floats on the surface of molten metal, an alloy chosen to have a low melting point — lower than that of glass. The glass is allowed to cool enough to solidify on the surface of the molten metal. Then you just pluck it out of the pool of molten metal. Not with your bare hands.

As a surface plate in a production line or for large metalwork, a pane of glass would be utterly worthless. But for the hobbyist working on a very small scale, a good, thick pane of glass works great.

We’re going to try using a pane of glass as a surface plate, depending on it to draw really straight lines. We’ll use it derive the centerline of a 2-1/2″ workpiece of 1″x1″ extruded aluminum. (This will only work, by the way, if we know the faces of the workpiece are flat — which we assume but won’t confirm, but could confirm with the pigment trick — and that the faces are parallel. But if it works — if we establish a centerline and can prove it — the parallelism of the workpiece faces will also be confirmed.)

That’s a tube of oil paint from the local art supply store. It’s Prussian blue. Here it’s being smeared onto one face of a small piece of 1″x1″ extruded aluminum. The main reason we’re using it is that scribed lines on bare metal can be hard to see, but a line scribed through a layer of pigment is bright and easy-to-see. We could have used a felt-tipped marker. But we like Prussian blue — it reminds us of finger-painting. Here’s the completed coating:

The scribe is clamped into a dial indicator holder doohickey with a magnetic base, which is stuck to a small piece of flat metal (stolen from an engineer’s metalworking protractor). Here the tip of the scribe has been adjusted to point approximately at the centerline of the workpiece. We intend to find the exact centerline. By simply sliding our scribe-dial-indicator-holder-doohickey-with-a-magnetic-base across the glass surface plate, we scribe a short test line:

We flip the workpiece and try to rescribe the same line, without readjusting the scribe:

When we examine the two test lines, we find that — as expected — they don’t quite align:

Now we adjust the scribe tip. We adjust it to fall between the first two test lines. We then make a new pair of test lines. We repeat the process until the tests lines are as well-aligned as we can make them:

Then, sliding our doohickey, we try scribing a complete centerline. Then we test the centerline: we flip the workpiece, and without adjusting the scribe, we try again, and we check for agreement along the full length:

The scribed lines match, under unaided visual inspection. Just for the heck of it, we added crosshairs. Now comes the fun part: we inspect the line we made:

More detail! We must magnify! We stick the workpiece under a microscope. Here we’ve inkjetted a small millimeter ruler on paper, and we’ve placed it directly below the scribed line, for comparison under the scope:

Our centerline is the single vertical line. Pretty freakin’ spot-on. The parallel scribed lines are our crosshairs. For the heck of it we check the height of the scribe tip:

It lies on the 1/2″ mark, and to the limits of our visual inspection, the alignment is perfect.

Best wishes — stochastic



lap microlathe

Today’s banner: the Taig MicroLathe. It’s adorable. It’s so small you can hold it in your lap. We’re completely serious:

How cute is that? You could pack it up in a box with some colored paper and take it to a crafting party!

We used it to make the very small collet featured in last week’s post, where we mentioned the need for a tiny slitting saw. Here’s how we did it:

The small silicon-carbide blade is mounted in a Dremel Rotary Tool, mounted to the Taig Lathe milling attachment using parts from a Vanda-Lay Industries Acra Mill Plus. Last week’s collet was parted from the piece of aluminum rod held in the lathe’s four-jawed chuck. Here’s the whole setup:

… One of the cats has made a guest appearance in our brand-new, absurdly-off-the-cuff photo studio. At night we can only see his eyes, which is kind of creepy. We can actually see him today, being as the backdrop is white…

Best — stochastic