The sons of Martha

Rudyard Kipling wrote a poem called ‘The sons of Martha‘ which is a gentle hymn of praise to those in society whose graft keep things going while others enjoy themselves. I like to think it’s about engineers. It contains a line which I really like: ‘They do not preach that their God will rouse them a little before the nuts work loose‘. If I’d paid a little more heed to that, I wouldn’t now have a pile of wreckage rather than a working drone. I failed to properly tighten the propeller nuts, and sure enough one came loose at altitude. It makes for an amusing video (I hope I haven’t given away the ending), but it may be a little while before the drone flies again.

Making things to make things to make things

I recently acquired a woodturning lathe. Unfortunately, it was missing a rather important part – the centre drive head, which grips the wood being turned. It’s not huge or complex. It just looks like an elongated nut with spikes on one end which grip the wood being turned. At the other end is an internal screw thread, which fits on to the drive shaft of the lathe:
drive_centre 1
Because the lathe is old (you can tell from the black and white picture), the manufacturer doesn’t sell the spare part any more. They don’t seem to appear on eBay, presumably because anyone with a lathe isn’t going to sell such an important component. If I had any significant metalworking machinery, I could make one – but I don’t (yet). I do have a 3D printer, however.

I didn’t do any stress analysis on the component, but my instinct told me that a printed part wouldn’t going to be strong enough for this job. The centre has to hold a largish lump of wood spinning at up to 3000rpm. It has to do this while the wood is carved by a chisel, and most importantly it has to do this while I am standing very close to it. It’s not allowed to break. The body of the part needs to be reasonably strong, and the spikes on the end doubly so. It’s not really printable unless you have a SLS metal printer. If I could afford one of those, I wouldn’t be buying an old second-hand lathe.

My solution was to cast a new component, and to 3D print the mould for it. Some years ago I came across Plastic Padding Chemical Metal, which is a two-part polyester resin filled with metal powder. It’s designed for repairing things, and it’s very strong when it sets. I’ve mended various things with it over the years, and none of them have ever failed. I thought I might be able to use it to cast a new part. My wholly unscientific feeling was that it ought to be strong enough for the body of the thing, but probably not for the spikes. For that purpose, some hardened steel masonry nails might do the job. Casting would allow me to embed the nails in the part, and to create the required femall screw thread by simply casting around the male one.

I used OpenSCAD to design a three part mould, and printed it:

This is actually the Mark III version. The first two did not have a separate end piece, and I eventually realised that once I had filled the mould with resin and put the nails in, I would not be able to separate it. Doh! One thing to bear in mind is that Plastic Padding is sticky. It’s designed as a repair material, so it’s intended to stick to things. I didn’t want it to stick to the mould, or to the screw thread on the drive shaft. To stop this, I lined the mold with sellotape, and covered the shft’s screw thread with a layer of PTFE plumber’s tape. You can’t beat a good bodge. Here’s how the mould looks, half assembled and almost ready for filling:


And here it is fully assmbled and filled with sticky goo, waiting for it to set:


After 20 minutes, I opened up the mould (you’ll have noticed the carefully-planned slots on the mould join line, for levering it apart) to reveal this mess:


Which eventually delivered a component which clearly needed a bit of cleaning up:


But it works! Just for entertainment, I mounted a 2″ square section block of cheap pine, and turned it into one of the roughest spindles you’ll ever see – but the Plastic Padding component worked fine:


Now I just need to learn how to turn wood properly…

Incidentally, I’m not sponsored by Plastic Padding. I’m not averse to them sending me a free pack, either 😉

Happiness is a clean head

I’ve not posted much about 3D printing for a while, largely because I haven’t ben able to get my printer to make a decent print without a lot of fiddling. Prints were rough, structurally weak, and generally unsatisfactory. I Tried all sorts of kludgy fixes, but nothing seemed to work reliably. I was beginning to think that the filament I was using was beginning to degrade (some of it is a year or more old). Then I had a conversation with a colleague about the 3D printers (Ultimaker II’s) at work. They were suffering similar problems, and were returned to good operation by replacing the print heads. It turns out that with sufficient usage, the tiny hole in the hot squirty nozzle (that’s a technical term) becomes both worn and partially blocked with overcooked filament residue. It’s a bit like the virtually indestructible stuff which accumulates on the the tins in which you roast vegetables. You do roast vegetables, don’t you? This (blocked nozzles, not ineffectually-cleaned roasting tins) results in a number of problems:

  1. Low extrusion rates
  2. Filament feed skipping, because it can’t push the filament hard enough
  3. Erratic extrusion

At work, we’ve started to think of the print head (or at least the extrusion nozzle) as a consumable item, to be replaced routinely after an as-yet undetermined quantity of filament has been extruded.

Why, I thought, couldn’t I try this at home? No reason at all. Apart from anything else, hotend technology has improved since I bought mine. It seems the generally-accepted best DIY print head is the e3dv6. It’s cleverly designed to separate the hot part from the rest by as small a thermal bridge as possible, and also has a built-in fan to keep the cool part cool. And unlike my old hotend, it’s got a separately-replaceable nozzle. So if (when) it does clog or wear out, it will be cheap to replace.


I bought one. Naturally, it needed a new part printing to fit it on to Richmond, but that was easy. And guess what? It works brilliantly. In a stroke, I’m back to creating smooth, accurate prints. Indeed, I’m tempted to say that the quality is better than the J-Head generated when it was new. I’m really quite chuffed.

Printed lathe parts online

Since I posted a video of my 3D printed lathe on YouTube, the video has now been viewed over 100,000 times. If a typical working day is 8 hours, and the working year is 250 days or so, then it’s the equivalent of about two solid years of someone watching it. That’s not a job I’d want.


Anyway, a number of people have asked for the STL files so they could make one themselves. I’ve finally got them in some sort of order, and you can now download a zip file with them all from here [wpdm_package id=’423′].

If you haven’t seen the video, here it is:

Cracking the cube

I can’t take any credit for this.

Earlier this summer, I built a Rubik’s cube solver from a Lego Mindstorms set. I simply followed the plans for the Mindcuber design. It seemed to work quite well, but my Rubik’s cube had one face which was much stiffer to rotate than others, and the power available from the Lego motors was insufficient to reliably turn it. So it’s been sitting in my office for a while doing nothing. Today, however, Rob lent me a speed cube he bought from Amazon. It’s designed to take as little torque as possible to rotate, and has nicely chamfered edges so it doesn’t jam if it’s slightly out of alignment when you try to turn it. In the picture, the speed cube is the one on the left.


The cube-solver robot loves it. I’ve posted a video of it on the YouTubes at .

The whole thing is a supremely pointless exercise, but it is rather hypnotic to watch.

…and we’re back!

As a close follower of my blog, you will doubtless have noticed that it has been off the air the last few days. I didn’t. Rob drew my attention to its non-existence. It turns out that there were hosting troubles, and to cut a dull story short I’ve had to move the blog to a different hosting provider.

It’s more or less fixed now, but still has a few niggles to sort out. Sorry for any inconvenience.

More tiny WiFi success

As I have posted before, I have been playing with the super-cheap WI07C WiFi module based on the ESP8266 chip. I’ve now had sufficient success with it that I can publish a post on a working project. This simple setup uses an Arduino nano to read temperatures from to 18BS20 sensors, formats the data as JSON and then sends it over WiFi to a server on my home network. It’s cheap and simple. Here’s the fritzing diagram:


You may notice the Adafruit level shifter board in there too. That’s because the digital IO from the arduino is 5V, but the WiFi module needs 3.3V. The Adafruit module is a dead easy way of joining the two. The temperature sensors use a three-wire protocol which allows you to connect many in parallel and address each one individually. there’s a software library which takes care of this.

Here’s the Arduino sketch. It uses Miles Burton’s temperature control library to read from the sensors, so you’ll need to download that. NB: this code is not a shining exaple of style or completeness. It’s a quick hack to get something working. It does no error checking or reconnection if there are problems. You may find yourself pressing the reset button a lot.

You might also note that the hardware serial port is required for the WiFi module, which needs 115200 baud. This means that you can’t upload a new sketch to the arduino while it’s connected to the WiFi module. I just whip out the wires to the TXD and RXD pins on the arduino while I’m uploading, and all is well.

The sketch tries to join the WiFi network, and then tries to establish a simple TCP connection to a server IP address and port of your choice. Once the connection is established, it checks the temperature sensors every 10 seconds or so and sends the temperatures to the server in JSON format, thus: {"temp":[22.63,22.81]}. That’s all it does. You’ll need a TCP server listening on your chosen IP address and port, of course. It seems to work quite reliably for me.

#include <SoftwareSerial.h>
#include <OneWire.h>
#include <DallasTemperature.h>

#define SSID        "MyHomeSSID"
#define PASS        "MyPassword"
#define TARGET_IP   "192.168.1.xx"
#define TARGET_PORT 5000

SoftwareSerial dbgSerial(10,11); // RX,TX
DallasTemperature sensors(&wire);

void setup()
   // WiFi module needs fast serial, so must use the hardware port which is also used for
   // uploading sketches

   // For debugging, we therefore need a software serial port.  This can be much slower.


  // Connect to the wirelsess network
  dbgSerial.println("Joining network...");

  // Just check that the WiFi module is joined to the network
  dbgSerial.println("Check connection...");

  dbgSerial.println("Initialising sensors...");

  dbgSerial.println("Connecting to server...");

  dbgSerial.println("Ready to rumble!");

int incomingByte=0;
bool echoLocal = true;

// Get the data from the WiFi module and send it to the debug serial port
void receive(){
  while (Serial.available() >0) {
    incomingByte =;

char temp1[10];
char temp2[10];

void loop()

  // call sensors.requestTemperatures() to issue a global temperature
  // request to all devices on the bus
  dbgSerial.print("Requesting temperatures...");
  sensors.requestTemperatures(); // Send the command to get temperatures


  String json="{"temp":[" + String(temp1) + "," + String(temp2) + "]}";
  dbgSerial.print("Sending ");

  // Send the data to the WiFi module


This is a work in progress. I’ll be updating it soon. But for now, I’m very pleased with the simplicity of the WiFi modules, and even more pleased with their low cost (I am a Yorkshireman, after all).

Success, of a sort

The recent modifications to my printer have made a huge difference.  Not only is it printing much more accurately, but I can print item after item without recalibrating.  There are further improvements to be made (aren’t there always?), but I’m now at a point where I can be reasonably confident of being able to print the parts I need to make modifications.  Here’s an example:


These two clamps are created so that I can mount a scavenged motor securely for my next project.  I modelled these in OpenSCAD, sliced them in Slic3er and printed them using Repetier-Host control software.  Everything just worked.  I haven’t mentioned Repetier-Host before, because I’ve only just become aware of it.  It’s a very nice front end for the printer, and manages Slic3r.  You can load and view a .STL file, slice it and print it from the same interface.  It’s slicker than Pronterface, which I had been using.  It’s definitely my software of choice now.  It makes it really easy to adjust the printing speed during printing – meaning that you can slow down the head for fiddly areas, and speed it right up for less important bits.

Flushed with success printing useful things, I thought it was time to try some frivolity.  Here’s a “Skull with pointed teeth”, from a model I found on thingiverse:


It’s about 5cm tall.  It would look better printed in white plastic, but I’ve only got blue.  I’m really pleased with this print.  Next time, I’ll make it hollow and mount a couple of red LEDs in the eye sockets…

Finally, I decided to try something more complex.  Printing objects with overhangs is not simple for this style of printer, because there is no surface deposit material on.  So I have not tried it before.  Slic3r has a setting you can use which will help to print overhangs by printing columns of expendable support material underneath.  These can then be cut away when the print is complete.  The example I tried is a minion from thingiverse (if you don’t know what a minion is, you should watch the film Despicable Me at once).  Here’s a picture of it mid-print:


It’s hard to see the shape, because of all the support material (the vertical columns at the front), but you can see the honeycomb-shaped fill of the main part.  When the print is finished, the poor minion looks like this:


Ten minutes with a scalpel, cutting away the scaffolding, and he looks like this:


He’s a long way from perfect, but given the size (about 6cm tall), it’s not too bad.  His arms are only about 3mm thick, and they could not have been printed as part of the main figure without support.   Again, it doesn’t help that he is translucent blue rather than yellow.  Perhaps a paint job will improve him.  A light sanding certainly would.