If you think about it, STL files are like PDF files. You usually create them using some other program, export them, and then expect them to print. But you rarely do serious editing on a PDF or an STL. But what if you don’t have anything but the STL? [The Savvy Engineer] has a method to help you if you need to reverse engineer an STL file in FreeCAD. Check it out in the video below.

The problem is, of course, that STLs are made up of numerous little triangles. The trick is to switch workbenches and create a shape from mesh. That gets you part of the way.

Once you have a shape, you can convert it to a solid. At that point, you can create a refined copy. This gives you a proper CAD file that you can export to a STEP file. From there, you can use it in FreeCAD or nearly any other CAD package you like to use.

Once you have a proper object, you can easily use it like any other solid body in your CAD program. This is one of those things you won’t need every day, but when you do need it, it’ll come in handy.

Want to up your FreeCAD game? We can help. There are other ways to hack up STL files. You can even import them into TinkerCAD to do simple things, but they still aren’t proper objects.

One downside of working with the old Inmos Transputer devices is the rarity and cost of the original silicon. Obviously, you can’t sidestep the acquisition of the processor—unless you emulate—but what about replacing the IMS C011/C012 link chip? You need this (expensive) part to interface the transputer to the programming host, but as [Erturk Kocalar] discovered, it’s perfectly possible to coax a Teensy to do that job for you just as well.

Transputers work by utilizing an array of bit serial interfaces to connect a network of devices, allowing for cooperative computation on tasks too large to fit on a single device. This protocol is, at its link level, a simple asynchronous bit serial affair, with 11-bit data messages, and a raw two-bit frame for the acknowledge. The C011 device at its heart is just a specialized UART—it takes 8-bit parallel data from the host, dealing with handshaking, and pushes it out to the first transputer in the chain at 5, 10 or 20 Mbps, but inverted and with two start bits and a single stop bit. In parallel, it performs the same task in the reverse direction.

[Erturk] realized that the Teensy UART has an inverted mode and, crucially, a 9-bit data mode. This allows the second start bit to be generated as bit 0 of the word, with the remaining eight bits forming the payload. Simple stuff. Additionally, the Teensy UART is capable of the maximum transputer bitrate of 20 Mbps, without breaking a sweat.

There is a slight issue, however, in that there is no way to send or receive the two-cycle acknowledgement frame directly. Since the protocol stop bit is a low, it is possible to implement this by simply sending a dummy data word with all 9 data bits low (since the acknowledge is a ‘1’, ‘0’ pattern). In one specific corner case, that of a direct memory PEEK operation, the command is clocked into the transputer, which sends back a two-cycle ACK—almost immediately followed by the 11-cycle data packet with the result. But, since the Teensy UART is still busy ‘fake decoding’ the full 11-bit dummy ACK message, it will miss the data packet entirely.

It turns out that the easiest way to get around this is to speed up the link and run at the maximum 20 Mbps rate. That way, the Teensy will have fully received the overly-long ACK long before the transputer has completed the PEEK command and started to send over the result. Why you would voluntarily run the link slower escapes us, once you’d got the design dialled in and reliability was a given, anyway.

We like transputers, a cool technology that died too soon. Here’s a quick guide to these innovative devices. Some people are really into transputer hardware, like this person. Finally, with the genuine hardware finicky to work with, expensive and hard to find, you could play along with your trusty web browser, and tick it off your nerdy bucket list.

During the AI research boom of the 1970s, the LISP language – from LISt Processor – saw a major surge in use and development, including many dialects being developed. One of these dialects was Scheme, developed by [Guy L. Steele] and [Gerald Jay Sussman], who wrote a number of articles that were published by the Massachusetts Institute of Technology (MIT) AI Lab as part of the AI Memos. This subset, called the Lambda Papers, cover the ideas from both men about lambda calculus, its application with LISP and ultimately the 1980 paper on the design of a LISP-based microprocessor.

Scheme is notable here because it influenced the development of what would be standardized in 1994 as Common Lisp, which is what can be called ‘modern Lisp’. The idea of creating dedicated LISP machines was not a new one, driven by the processing requirements of AI systems. The mismatch between the S-expressions of LISP and the typical way that assembly uses the CPUs of the era led to the development of CPUs with dedicated hardware support for LISP.

The design described by [Steele] and [Sussman] in their 1980 paper, as featured in the Communications of the ACM, features an instruction set architecture (ISA) that matches the LISP language more closely. As described, it is effectively a hardware-based LISP interpreter, implemented in a VLSI chip, called the SCHEME-78. By moving as much as possible into hardware, obviously performance is much improved. This is somewhat like how today’s AI boom is based around dedicated vector processors that excel at inference, unlike generic CPUs.

During the 1980s LISP machines began to integrate more and more hardware features, with the Symbolics and LMI systems featuring heavily. Later these systems also began to be marketed towards non-AI uses like 3D modelling and computer graphics. As however funding for AI research dried up and commodity hardware began to outpace specialized processors, so too did these systems vanish.

Top image: Symbolics 3620 and LMI Lambda Lisp machines (Credit: Jason Riedy)

Vector Control, also known as Field Oriented Control or FOC is an AC motor control scheme that enables fine-grained control over a connected motor, through the precise control of its phases. In a recent video [Excessive Overkill] goes through the basics and then the finer details of how FOC works, as well as how to implement it. These controllers generally uses a proportional integral (PI) loop, capable of measuring and integrating the position of the connected motor, thus allowing for precise adjustments of the applied vector.

If this controller looks familiar, it is because we featured it previously in the context of reviving old industrial robotic arms. Whether you are driving the big motors on an industrial robot, or a much smaller permanent magnet AC (PMAC) motor, FOV is very likely the control mechanism that you want to use for the best results. Of note is that most BLDC motors are actually also PMACs with ESC to provide a DC interface.

The actual driving is done with two MOSFETs per phase, forming a half-bridge, switching between the two rails to create the requisite PWM signal for each phase. Picking the right type of MOSFET was somewhat hard, especially due to the high switching currents and the high frequency at 25 kHz. The latter was picked to prevent audible noise while driving a robot. Ultimately SiC MOSFETs were picked, specially the GeneSiC G3R30MT12K. Of note here are the four legs, with a fourth Kelvin Source pin added. This is to deal with potential gate drive issues that are explained in the video.

With the hardware in place, whether following the [Excessive Overkill] GitHub projects or not, what makes all of it work is the software. This is where the microcontroller aspect is essential, as it has to do all the heavy lifting of calculating the new optimal vector and thus the current levels per phase. In this controller an STM32F413 is used, which generates the PWM signals to drive the half-bridges, while reading the measurements from the motors with its ADC.

As can be seen in the resulting use of this controller with old industrial robots, the FOC controller works quite well, with quiet and smooth operation. This performance is why we’re likely to see FOC and PMAC motors used in applications like 3D printers in the future, though the rule of ‘good enough’ makes the cost of an FOC controller still a tough upsell over a simple open loop stepper-based system.

Let’s say you want to blink an LED. You might grab an Arduino and run the Blink sketch, or you might lace up a few components to a 555. But you needn’t go so fancy! [The Design Graveyard] explains how this same effect can be achieved with a single transistor.

The circuit in question is rather odd at first blush. The BC547 NPN transistor is hooked up between an LED and a resistor leading to a 12V DC line, with a capacitor across the emitter and collector. Meanwhile, the base is connected to… nothing! It’s just free-floating in the universe of its own accord. You might expect this circuit to do nothing at all, but if you power it up, the LED will actually start to flash.

The mechanism at play is relatively simple. The capacitor charges to 12 volts via the resistor. At this point, the transistor, which is effectively just acting as a poor diode in this case, undergoes avalanche breakdown at about 8.5 to 9 volts, and starts conducting. This causes the capacitor to discharge via the LED, until the voltage gets low enough that the transistor stops conducting once again. Then, the capacitor begins to charge back up, and the cycle begins again.

It’s a weird way to flash an LED, and it’s not really the normal way to use a transistor—you’re very much running it out of spec. Regardless, it does work for a time! We’ve looked at similar circuits before too. Video after the break.

[Thanks to Vik Olliver for the tip!]

Making nylon plastic from raw chemicals used to be a very common demo; depending where and when you grew up, you may well have done it in high school or even earlier. What’s not common is taking that nylon and doing something with it, like, say extruding it into filament to make a benchy. [Startup Chuck] shows us there might be a reason for that. (Video, embedded below.)

It starts out well enough: sebacoyl chloride and hexamethaline diamine mix up and do their polymerizing tango to make some nylon, just like we remember. (Some of us also got to play with mercury bare-handed; safety standards have changed and you’ll want to be very careful if you try this reaction at home). The string of nylon [Chuck] pulls from the beaker even looks a little bit like filament for a second, at least until it breaks and gets tossed into a blobby mess. We wonder if it would be possible to pull nylon directly into 1.75 mm filament with the proper technique, but quality control would be a big issue. Even if you could get a consistent diameter, there’d likely be too much solvent trapped inside to safely print.

Of course, melting the nylon with a blowtorch and trying to manually push the liquid through a die to create filament has its own quality control problems. That’s actually where this ends: no filament, and definitely no benchy. [Chuck] leaves the challenge open to anyone else who wants to take the crown. Perhaps one of you can show him how it’s done. We suspect it would be easiest to dry the homemade nylon and shred it into granules and only then extrude them, like was done with polypropylene in this mask-recycling project. Making filament from granules or pellets is something we’ve seen more than once over the years.

If you really want to make plastic from scratch, ordering monomers from Sigma-Aldrich might not cut it for ultimate bragging rights; other people are starting with pulling CO2 from the atmosphere.

Thanks to [Chaz] for the tip! Remember that the tips line isn’t just for your successes– anything interesting can find its home here.

If you want to print, say, a book, you probably will type it into a word processor. Someone else will take your file and produce pages on a printer. Your words will directly turn on a laser beam or something to directly put words on paper. But for a long time, printing meant creating some physical representation of what you wanted to print that could stamp an imprint on a piece of paper.

The process of carving something out of wood or some other material to stamp out printing is very old. But the revolution was when the Chinese and, later, Europeans, realized it would be more flexible to make symbols that you could assemble texts from. Moveable type. The ability to mass-produce books and other written material had a huge influence on society.

But there is one problem. A book might have hundreds of pages, and each page has hundreds of letters. Someone has to find the right letters, put them together in the right order, and bind them together in a printing press’ chase so it can produce the page in question. Then you have to take it apart again to make more pages. Well, if you have enough type, you might not have to take it apart right away, but eventually you will.

Automation

That’s how it went, though, until around 1884. That’s when Ottmar Mergenthaler, a clockmaker from Germany who lived in the United States, had an idea. He had been asked for a quicker method of publishing legal briefs. He imagined a machine that would assemble molds for type instead of the actual type. Then the machine would cast molten metal to make a line of type ready to get locked into a printing press.

He called the molds matrices and built a promising prototype. He formed a company, and in 1886, the New York Tribune got the first commercial Linotype machine.

These machines would be in heavy use all through the early 20th century, although sometime in the 1970s, other methods started to displace them. Even so, there are still a few printing operations that use linotypes as late as 2022, as you can see in the video below. We don’t know for sure if The Crescent is still using the old machine, but we’d bet they are.

Of course, there were imitators and the inevitable patent wars. There was the Typograph, which was an early entry into the field. The Intertype company produced machines in 1914. But just like Xerox became a common word for photocopy, machines like this were nearly always called Linotypes and, truth be told, were statistically likely to have been made by Mergenthaler’s company.

Kind of Steampunk

For a machine that appeared in the 1800s, the Linotype looks both modern and steampunk. It had a 90-key keyboard, for one thing. Some even had paper tape readers so type could be “set” somewhere and sent to the press room via teletype.

The machine had a store of matrices in a magazine. Of course, you needed lots of common characters and perhaps fewer of the uncommon ones. Each matrix had a particular font and size, although for smaller fonts, the matrix could hold two characters that the operator could select from. One magazine would have one font at a particular size.

Unlike type, a Linotype matrix isn’t a mirror image, and it is set into the metal instead of rising out of it. That makes sense. It is a mold for the eventual type that will be raised and mirrored. The machine had 90 keys. Want to guess how many channels a magazine had? Yep. It was 90, although larger fonts might use fewer.

Different later models had extra capabilities. For example, some machines could hold four magazines in a stack so you could set multiple fonts or sizes at one time, with some limitations, depending on the machine. Spaces weren’t in the magazine. They were in a special spaceband box.

Each press of a key would drop a matrix from the magazine into the assembler at the bottom of the machine in a position for the primary or auxiliary letter. This was all a mechanical process, and a skilled operator could do about 30 words per minute, so the machines had to be cleaned and lubricated. There was also a special pi channel where you could put strange matrices you didn’t use very often.

Typecasting

When the line was done, you pressed the casting level, which would push the matrices out of the assembler and into a delivery channel. Then it moved into the casting section, which took about nine seconds. A motor moved the matrices to the right place, and a gas burner or electric heater kept a pot of metal (usually a lead/antimony/tin mix that is traditional for type) molten.

A properly made slug from a Linotype was good for 300,000 imprints. However,  it did require periodic removal of the dross from the top of the hot metal. Of course, if you didn’t need it anymore, you just dropped it back in the pot.

Justification

You might wonder how type would be justified. The trick is in the space bands. They were larger than the other matrices and made so that the further they were pushed into the block, the more space they took. A mechanism pushed them up until the line of type exactly fit between the margins.

You can see why the space bands were in a special box. They are much longer than the typical type matrices.

How else could you even out the spaces with circa-1900 technology? Pretty clever.

If you have been paying attention, there’s one major drawback to this system. How do the matrix elements get back to the right place in the magazine? If you can’t automate that, you still have a lot of manual labor to do. This was the job of the distributor. First, the space bands were sorted out. Each matrix has teeth at the top that allow it to hang on a toothed distributor bar. Each letter has its own pattern of teeth that form a 7-bit code.

As the distributor bar carries them across the magazine channels, it will release those that have a particular set of teeth missing, because it also has some teeth missing. A diagram from a Linotype book makes it easier to understand than reading about it.

The Goldbergs

You have to wonder if Ottmar was related to Rube Goldberg. We don’t think we’d be audacious enough to propose a mechanical machine to do all this on top of an automated way to handle molten lead. But we admire anyone who does. Thomas Edison called the machine the eighth wonder of the world, and we don’t disagree. It revolutionized printing even though, now, it is just a historical footnote.

Can’t get enough info on the Linotype? There is a documentary that runs well over an hour, which you can watch below. If you’ve only got five minutes, try the short demo video at the very bottom.

Moveable type was to printing what 3D printing is to plastic manufacturing. Which might explain this project. Or this one, for that matter.