Archive for One-day Builds

A Quick Re-Intro to the Lathe

As my current favourite project is primarily a software one, I really need something on the side to keep my hands busy.


So I opted to do a small, easy metal lathe project. You know how those go, right?

It ended up taking over 40 hours, mostly because I am bad at this. But I learned a lot!


Here is the excellent old-school lathe I used:


Initially, this was going to be all brass, but Metal Supermarket doesn’t really carry a lot of red metals. Metal Supermarket is awesome, but pretty much the only stuff they carry is solid brass rod. It’s difficult to get a concentric hole through the entire length required by a pen, so that doesn’t work too well.

While browsing their stock, though, I found some gorgeous thick-walled stainless steel tube stock. Had to buy it.


I started out without a complete plan of what I was trying to do, and it’s clear that I was just playing around with shapes.


So I decided I liked that, parted off the left side, and machined some brass rings to go around the grip as extra bling.

You can see the scales I was working at, this all ended up being pretty precise work. Our lathe is a little large to comfortably get in to close features with the tailstock in use, but it’s still possible when you’re careful.


This piece had no way to effectively join it to the other side of the pen due to lack of forethought, so it had to be scrapped.

The next version was a little bit better, and shows the steel-brass-steel ring pattern, and kinda how everything fits together.

But then, one of the biggest takeaways I learned on this project is that working with stainless steel suuuuuuucks.


It’s really malleable, and is able to bend with low forces, even less than an inch away from where it’s being held.

Due to the high carbon content, it’s super hard on the tools and required frequent resharpening. When the tools are dull, the metal goes straw-coloured due to heat treating really quickly, and gets even harder.

So here’s attempt number three. I’m at about thirty hours by now, but getting faster after every failure.


I’ve attempted to fix everything together with superglue for machining, but there are issues with that. I’ve seen people use superglue for all sorts of workpiece holding in brass, but brass is really soft and easy to work with. While trying it with steel, the forces are much greater, in addition to the steel getting warm and melting the glue. Basically an exercise in frustration and not really worth it (for steel).

Nevertheless, regluing often and working slowly eventually starts to get results.






Attempt number four used a separate aluminum piece that I machined into a very thin-walled tube – about one quarter millimetre walls – instead of a single steel piece, because it’s much easier to work with.


Abandoning superglue, I tried using silver solder. This was a risky prospect, because aluminum forms oxide layers that don’t adhere well to solder, and stainless steel just doesn’t wick until very high heats. So I used a MAPP gas torch, liquid flux, and silver solder, which resulted in…


My brass rings melted right off the tube. Was not expecting that.


Okay, attempt number five. This was a tube I machined out of mild steel with the brass rings, and only silver solder between them instead of alternating with steel.


As opposed to stainless steel, mild steel was really easy to work with and soldered to well. It oxidises, though, not acceptable for anything on the outside of the pen. So it needs a sheath on either end.


And then roughing it out. Superglue works fine for the final steps, because there are no cutting forces trying to tear it apart.


Filing and finishing it. So much filing. Part of the reason this project took so long is that between each of these steps, there’s one or two hours of filing to make all of my interference fits work.


Afterwards, I sanded from 180 grit all the way up to 600 and then emery paper. It was mirror finish by the end, and with a little bit of polyurethane varnish used to seal it all in.

As you can see, the idea is to hold a standard Bic pen cartridge, nothing fancy. Next pen can be more complicated, I wanted this one done quickly. Things I learned:

  • Stainless steel is The Worst
  • Silver solder actually looks great and is easy to work with
  • Stainless steel is so bad
  • Those Youtube videos where they lightly touch the piece with an emery board after they finish machining? They’re cutting like an hour minimum of work out of the video
  • I’m never working with stainless steel again

I’m done with this project, but there are definitely some things I’m not totally happy with, to be fixed for the next one:

  • I built a little pocket clip using spring steel and hammers , but never ended up putting it on
  • There are tool marks on the front portion
  • The very front edges has a little lip from the mandrill deforming it
  • I didn’t let the varnish set properly, so it’s coming off a little
  • There should be some tactile difference where the grip is, it turns out this pen is a little hard to pick up and use without looking at it.


I’ve posted here before about my troubles with flexible flat connectors. Well, not directly, but that always seems to be a tangential obstacle in the already perilous minefield of hardware hacking.
Basically, I hate them and I want them to go away.

The answer is, obviously, a breakout board, but I was having trouble finding exactly what I wanted. The system that I was having trouble with is 0.14mm pitch, and an odd number of pins. That means that the connector’s pins are staggered instead of directly across from one another. Slightly unusual, and I couldn’t find an inexpensive breakout board for it.

Over an evening, I started designing a board that should help. The idea is to keep a few of these boards on hand, and if you’re working with an FFC cable with a pitch of 0.14mm, toss an extra cable and a couple connectors onto your next Digikey order. Should run you a couple bucks.

In choosing what kind of connectors I wanted the board to support, I had some decisions to make. Odd or even pins? How many?

I solved those by parsing Digikey’s catalogue:

FFC Chart


A general theory is that the more connectors of a certain pin count in the catalogue, the more common it is in the wild. As shown, it’s definitely important to support more than 30 pins. There’s another big spike at each common count, ending at about 51. That settled that.

There was another clever idea involved: the centre of the board is a flat cable connector footprint, with a little bit of a tweak. The middle row of pads correspond to pin 1, and every second pin after that. Depending on whether your connector has an even or odd pin count, you use the outer row of pads that are in-line or staggered, respectively. Those all break out to the pin headers as shown on the silkscreen.
There’s your breakout. If you need your cables connected to the device under test, use two boards, solder female header pins on one, male on the other, and sandwich them together, both connectors on either the inside or the outside as shown.

Obviously this may cause issues with length-matched traces, but you know. Cross your fingers. Worth a shot.

Future goals: Actually draw the traces myself, because the autorouter is terrible. I just wanted to spend as little time on this as possible.




It seems to work fine, though. I’m not trying to get GHz signal through it or anything.


You can get one through dirtypcbs here, or I’ll release the files when I eventually dig them out and make the traces pretty.

I like candy. Do you like candy?

At a place that I hang out on very rare occasions, there’s a big red button.



When somebody holds it, it starts up an air raid siren that can get really loud. Unfortunately, it spins up very slowly, so people let off as soon as they figure out what the button does. That results in one tiny little blip of the siren, barely enough to bother anyone. That’s no good at all!


So for this build, I didn’t want to spend very long at it, and attempted to do everything very roughly and as quickly as possible. I found all of the appropriate components kicking around, and designed around those.

Here’s what I came up with:



I found a transformer with outputs that measure at about 12VAC. 10:1 winding ratio, I guess. After rectification and smoothing, it’s a little over 18VDC. On the right side, I used an ALA2F12, a 12V relay. The transistor is a 2N3604, just a very generic NPN BJT because this application doesn’t require anything special.

The original button was just the AC line voltage to the fuse, then through the switch to the load, very very basic.


Okay. Starting from the left:

  • Transformer outputs at 12 volts or so,
  • through the half-wave rectifier diode (1N4007 I think) – results in 12 * root 2, about 18V,
  • big filtering capacitor (200v, 820uF),
  • 1MΩ bleeder resistor so the system doesn’t hold charge indefinitely,
  • original switch (connected to the big red button),
  • 100Ω resistor(to prevent sparks)
  • into timing cap (160v, 220uF) – charges to full very quickly,
  • another bleeder resistor,
  • Rb controlling current going into the transistor’s base (more on this later),
  • BJT  base.
  • At the top: resistor controlling going into the relay coil,
  • relay coil,
  • BJT collector going to ground.


Because I’m abusing a 12V relay by driving it with 18V, I had to compensate for that a little. According to the data sheet, the coil is nominally 272Ω, taking 43mA of current. Ignoring the transistor’s collector-emitter voltage (probably ~0.2V): 18v / 43mA – 272Ω = 146Ω. So I tossed a 150Ω resistor in series with the coil, and it seems to work.


For the base of the transistor, this resistor (along with the capacitor) is what controls the active time of the system. It also controls the maximum current that can conduct through the collector-emitter junction of the 3604 Typically the gain of those are in the 70-100 range, so current going into the base should be Ib = 43mA/100 = 0.43mA. Base-emitter junction is around 0.7v, so the base resistor can be figured out by 18v – 0.7v / Ib when the base cap is fully charged. Overdrive Ib to 1mA to ensure max-on, so I used 18kΩ.

I tested everything to check timing issues, overheating, etc., and it works well. The relay gets latched for about 7 seconds, which is perfect. If I cared about being more precise with that, or wanted to change the timing values, it’s pretty simple to treat that portion as an RC circuit and tweak the resistor or capacitor values.

So I built it

Perfect! Start to finish, took about seven hours. Not including the abortive first attempt last week.

So before, when newcomers pressed the button, there was only a very short blip of the air raid siren. Now, the thing latched for a good seven seconds. And it gets very loud in that time.

Stop-gap PCB creation (has stopped)


This is a year-old post that I never published. I guess I was waiting to be able to snap some pictures, but that never happened. Most of these components have been e-wasted by now.

I’ve talked about various avenues of rapid prototyping circuit boards before, and not really come up with any definitive solutions.

My current favourite possibility is using a dye-sublimation printer, but they’re fairly difficult to get ahold of. I’m not willing to throw money at the solution just yet.

In the meantime, one of the more reliable methods is toner transfer, using a clothing iron. There are two easily-controlled variables that affect the transfer quality. There are a lot more than two, but those are the ones that involve a human element.

As a solution to that, I started work on my own laminator. I took the fuser from a laser printer and mounted it to a board.

Mounting and getting it working independently had a fairly involved process. First I needed to drive the motor.

It required a lot of torque and I have no access to any simple motor that can handle that. The only thing I have that comes close is one of my brushless DC motors, but man, I don’t want to use complicated driving circuitry for that. What I ended up doing is mating a simple 12v DC motor to the gearing for one of those motors. I laser cut a bracket that has mounting holes for both sides, ground down a shaft, and it seems to work. A very consistent and slow speed, and huge amounts of torque.

The next step was the heating element. I ran it off one of the 30v supplies we have kicking around, and it got to the “reasonably warm” level while drawing just over 1 amp. Fortunately (or unfortunately, depending on your perspective), a local e-cycle company was closing down and had an impromptu fire-sale. I picked up a 60v power supply that was labelled “broken” for free. Replaced a PTC (that literally crumbled away in my hands), and it was good to go again. The new supply got it to “properly hot” in a minute or less.

The next step was measuring the temperature. The fuser had a thermister output that starting at around 33kohms. As it gets hotter, the resistance drops. I measured around 19kohms when it was “slightly hot”. That’s the totally objective temperature description I’m going with here.

I used a voltage divider with a 100k potentiometer to tune it to 0xFF at room temperature. The reasoning being that I didn’t actually need to know the “proper” lamination temperature, just the relative values that apply to this system.

So I had the whole system, the drive motor, the heater element, the temperature measurement. It turns out that while my system is 0xFF at room temperature, everything melts at 0xA0. That’s not very hot at all! I think. I have no idea what that translates to in real measurements.

There is another printer kicking around that I should be able to pull the fuser out of. The rollers didn’t really feel that hot overall when they melted, so it’s possible that it was just because I wasn’t running the motor at the same time.

Fortunately, there’s no shortage of old laser printers destined for the scrapheap.


I prefer to do most of my laser-cutting purely in 2D. The open-source vector software Inkscape totally rocks my socks off, and I can design things about three times faster using that than anything else.


When a design gets a little complicated, though, or it’s hard to see how everything fits together, it’s sometimes easier to model everything in 3D right from the start. So I built a linear actuator with SolidWorks.


If you can’t see, it’s a DC motor that rotates a threaded rod, with that slider piece in the middle holding a captive nut and a rod. You drive the motor, the rod goes in (or out).


This was just a proof-of-concept to see how it all fit together. I wasn’t really happy with:

  • The amount of material it used up
  • The physical size
  • Way too much friction in the system
  • Possible strength issues in the rod
  • No way to read or track the rod position.

Solution: Mark II.

  • Replace the DC motor with a stepper
  • Triangular chassis for less material usage and size
  • #10 threaded rod instead of 1/4″, also for size
  • Add some bearings
  • Triple up the actuator rod.

It’s very slow, but that’s simply a matter of choosing different motors and is acceptable for now.

The bearings I had on hand are standard axial bearings; totally not suited to radial loads. That’s something I’ll have to come back to. I saw a method of laser-cutting the races to make custom thrust bearings recently, I’ll have to see if that’s appropriate for this application.

Terrible picture, will be replaced

Terrible picture, will be replaced

20 Percent Time

Laser-etching is a modern process that effectively carves a 1-bit image onto a material. A lot of very cool images can be made with it, given enough artistic talent. I’m not one of them.
Fortunately, all that heavy lifting has been done for me by artists far more talented than me. In the 16th century (and on), making and selling prints was popular with European artists.

That means that there’s a wealth of royalty-free images out there that lend themselves excellently to laser-etching, simply by googling the term “woodcut.”


Here are a couple things I’ve been doing in the background while designing something else.