Sunday, August 30, 2009


Giving Mendel Teeth

I am particularly fond of Vik's bath-plug drive, but it's too lumpy for the X and Y axes. His model-helicopter belts will work well for these, but we can't print the drive gears for them, as the teeth are a bit too fine.

Toothed timing belts are a perennial problem for RepRap: we can reprap drive gears for the 5-mm (0.2") pitch ones with no difficulty, but not for a finer pitch. But the 5-mm pitch belts generally have a minimum width of 10mm, whereas we really need 5mm-wide belts. Otherwise the whole thing gets too chunky.

I think I finally have a solution: split a 10mm-wide belt to give two 5mm-wide ones. I made a jig...

...that you can put the belt in, stab it with a box-cutter/Stanley blade, then pull the belt through. The AoI file for this is in the Mendel section of the subversion repository here. Because timing belts have cords (usually kevlar or steel) running along them lengthwise to stop them stretching, the split works particularly cleanly as it cuts between two cords. And 10mm-wide belts with 5mm (0.2") pitch seem to be universally available and cheap. You can see the result at the top of this post.

I've designed a belt drive gear (here) that you can also see on the NEMA 14 motor at the top. This should work for all three axes of Mendel.

Incidentally, when reprapping something like this with a low cross-sectional area there can be problems with each layer of the part getting too much material deposited on it if you use the same reprapping settings as for larger parts. To avoid this:

  1. Print the part along with other things of the same height or higher (this effectively increases the cross-sectional area), and
  2. Increase the layer thickness slightly. I use 0.3mm for normal builds, and 0.5mm for tall thin things.

The drive gear does need the motor shaft to be filed to have two flats:

The way to do this is to:

  1. Put Blu-tack in the bearing hole to prevent iron filings getting in the bearing,
  2. Clamp the shaft, not the motor; carefully get it parallel to the vice by eye,
  3. When filing, check frequently: if the flat shape is a rectangle, it's parallel to the axis; if it's a trapezium, it's not.
With a little care you can get the size right within 0.1mm.

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Mendelssohn Z axis operational

I've got the Z axis going on the Mendelssohn design. In the picture here (RepRap is tilted so the bottom faces the camera) you can see the ball-chain drive connected up to the two Z threaded drive bars. The shiny pulley is a 608 bearing with some great big washers either side of it. Side note: If you put M4 nuts on an M4 bolt, the exterior diameter of the nut is 8mm and it fits perfectly as the axle for a 608 bearing.

The 4.5mm beaded chain gears are the same as used on the RepRap Child/Phoenix machine that built Mendelssohn. Printing a gear with a grub screw and captive nut was too hard, so I devised a clamp-on gear that fastens onto the NEMA17 shaft using an ordinary hose clamp. The tensioning pulley makes installation of the Z drive chain much easier on this prototype than the Darwin.

If you want to see it in operation, here's a video of it. I've stuck a mole grip on the X axis to add a bit of weight, and in case you can't see the ammeter it's running at 250mA. It ran like this for 20 mins, cycling up and down without overheating the motor or the EasyDriveV3 stepper driver. The OLPC is just powering the Arduino board - though some magic is needed to stop the OLPC powering down its USB ports at inconvenient moments. Once that's sorted I'll be able to power a RepRap using Ralith's minimalist RepRap command line utilities.

Vik :v)

PS I've since made the Y axis move back & forth using helicopter belt but need to print new bits to do it properly. People are asleep now, so I'll leave that for tomorrow.

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Thursday, August 27, 2009


Mendelssohn Update

Well, you've seen the nice diagram from Ed so here's what the framework looks like when you put it all together. One change becomes immediately apparent - there is no longer room for a cat to hide inside or under it. Things seem to basically fit, though it might be an idea to wrap tape or plastic shim around the Y bars to ensure they're gripped firmly.

There is a little flexion at the top of the assembly. It is possible that with the right speed of head movement at the right height we could get some vibrations building up, however I have not fitted the board holder or the Z axis guides, which may well add more rigidity.

The extruder holder is a simplistic design, basically because there are not enough 625 bearings in my part of NZ to build a Mendel (Gary just cleaned out the local supplier!). I found PLA on silver steel slides just beautifully, so I'll be using that approach for the prototyping. For the vertical guides I'll probably just push some CAPA in for the moment.

So, now comes the tricky bits - saddles, gears, pulleys etc. This prototype will probably experiment with 3 types of belt drive - 4.5mm ball-chain as successfully used on Darwins for the Z, E-Sky EK1-0503 model helicopter belt (sadly not quite long enough for the proposed X axis) on the Y, and if I can print gears for the 3.5mm ball-chain that'll go on the X axis. If not I'll install the standard Darwin X belt.

Vik :v)

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Wednesday, August 26, 2009


Wedge progress

Well, as you can see the Wedge has come a long way since the first concept, and after some critical design changes we’re close to knowing whether it’ll qualify as a cartesian design for Mendel (the next RepRap printer release).

Vik’s already introduced it below and is working hard on a prototype as we speak, but I thought I’d chuck out a few tasty details. Those with a Darwin may appreciate some of the latest specs:

- The footprint is 420 mm x 420 mm, with a cantilevered x-axis of length 512 mm. Height is 345 mm.
- Print area is currently 160 mm x 220 mm. This could be improved to 200 mm x 220 mm with the use of the Bowden extruder (which could rely on a smaller carriage)
- Print height will be ~ 160 mm.
- Assembly requires only 3 different bolt sizes (M4 x 40, M4 x 16 and M3 x 20).
- Axes run on bearings (624s and 608s). The beauty of the wedge configuration is that axes are not over-constrained… this means that all axes can be easily powered with NEMA 14 motors. Motor brackets are also compatible for NEMA 17s.
- Top gantry available for tool-head changer

We’re building a prototype in our lab as well. I’ve had a lot of requests for documentation – this will follow in good time. It’s one thing to knock up something that works… but getting things user-friendly for the rest of the world is a different kettle of fish entirely. I should say that the RepRap lab here at Bath University is working flat out to get it out asap, so your patience would be greatly appreciated over the next few months ;-)

Meanwhile here’s a VRML of the general assembly so far to get your teeth stuck into.

Friday, August 21, 2009


Buying a Rapman

After some weeks of soul searching and accepting the fact that my day job has cut rather severely into the time I have to devote to Reprap, I arrived at the conclusion that I could address my research agenda much more efficiently if I simply bought a 3D printer rather than rebuild Tommelise 2.0 or build an all new Tommelise 3.0 to do printing.

There are currently two full kit Reprap machines, the Makerbot and the Rapman. Although I was seriously considering using a Makerbot extruder with Tommelise 2.0, when I made the decision to buy a full, separate printer a few days ago I decided to go with the Rapman. It was a tough decision given the price differential between the two. The Rapman choice hinged primarily on what appears to me to be much more personally familiar PIC-based electronics used in the Rapman. What really sold me, however, was Batist Leman's videoclip published in the Builders' blog a few days ago. It was one thing to know intellectually that the Rapman could run autonomously from an SD card. It was quite another to see Batist demonstrate it.

I am going to keep Tommelise 2.0 as a milling machine. It is very good at that. The Rapman I hope to use to generate parts for Tommelise 3.0 and, more importantly, to extend the know how for the turkey bag approach that Adrian demonstrated a few months ago. I purchased another Rapman extruder to use exclusively with HDPE. If the turkey bag approach gets HDPE warping under control we will have effectively halved the price of feed stock for Reprap machines and captured a huge waste plastic resource if and when we get recycling working.

I am also hoping to get back to the research thread I started a year ago to develop a printable stepper motor. Having a reliable 3D printer should advance that cause considerably.


Mendel Sighted In The Wild

A structure that could be the beginning of a Mendel has been seen lurking in the workshop. It must be stressed here that Mendel is not yet even in alpha status, so changes in design are almost guaranteed. But thanks to the miracle of Open Source, those who enjoy building stuff that hasn't been designed yet can join in the fun.

Because this one is being printed by Phoenix, the original Child RepRap, I've decided to call it "Mendelssohn." This will make Mendelssohn a 3rd generation RepRap. Although it looks - and is - a lot smaller than the Darwin design, Ed's cunning artifices have made a machine with a greater printable area than the original Darwin. It'll be a lot easier and cheaper to put together too - after we've fiddled with it for a bit.

Now to convert the rest of the pieces into gcode...

Vik :v)

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Monday, August 17, 2009


RepRap at Hacking at Random 2009

I just got back from HAR2009 in Holland - an amazing event, and many thanks to the organizers for inviting me to give a talk. As I walked through the main gate, the first sight that greeted me (bottom left) was a RepRap that someone had left on a picnic bench while they went to pitch their tent. So I knew that this would be cool.

There were many reprappers there. But in particular I'd like to thank Erik de Bruijn, Marius Kintel, Philipp Tiefenbacher and Siert Wijnia - when I set up my talk, they all came onto the stage with their machines and got them running. A sort of mass repraping...

There were some other guys who set up their repstraps too, but unforgivably I didn't write down their names. Sorry. If they e-mail me, I'll add them to this post.

More pictures here.

Friday, August 14, 2009


Simple PWM Output Design - Spoondriver

This is how I've managed to build one channel of a budget PWM driver without using a circuit board or solder. Yes, the essential driver components minus blinking lights fit comfortably on a piece of 5 module long small terminal strip. In this photo the spoondriver is connected to a thick pair of power leads, a thin pair of drive leads which in this case power a fan, and a yellow lead which goes off to an Arduino output or similar.

The spoon? Oh, if you're driving a device that consumes an amp or four, you'll need a heatsink. I always hated those cheap, shoddy spoons and raided the cutlery drawer. There's one spoon that won't get stuck in my drawer again.

Vik :v)

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Sunday, August 09, 2009


Slicing and dicing with image processing

In which your narrator rebuilds Tommelise’s Slice and Dice app.

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Friday, August 07, 2009


ReplicatorG 0006 Available

ReplicatorG 0006 is now available for your replicating pleasure! (Well, if you’re using Linux or Windows. Mac OS X users, you’ll have to wait until I get to do a Mac build in the morning.) This release should make life a little easier for those of you who have been having serial port configuration issues. Other fun enhancements include:

* Per-axis motor inversion (requires v1.2 firmware)
* More reliable build aborts
* An optional in-build temperature readout (disabled by default, but can be turned on in the preferences)

Download it here! A more detailed changelog follows after the cut.

0006 changelog:

* Removed editor status bar
* 64-bit Mac OS X fix (courtesy Andreas Fuchs)
* Pass a GCode file in as a command-line parameter (courtesy Andreas Fuchs)
* Moved machine status below buttons and cleaned up display
* Ensure abort signal is sent to S3G on stop
* Display temperature of nozzle during builds (disabled by default)
* Add pref for temperature display
* Simulator2D optimizations, faster draws
* Reenabled Ctrl-J shortcut for control panel
* Use port names specified in XML by default, fall back to autoscan if not present
* Allow autoscan disabling for machines with scan problems
* Added support for writing onboard configuration data to the machine EEPROM
* Numerous small bug fixes
* New skeinforge version
* Larger max heap size on Mac OS X

A brief word on the new serial port selection routine: if you explicitly define the “portname” tag in your machines.xml, ReplicatorG will attempt to connect to that port immediately. Otherwise, it will by default autoscan your serial ports to find a working machine. If you want to manually select your serial port (say, because ReplicatorG is hanging while trying to scan one of your other serial ports) you can turn the autoscan funtion off by unchecking it in the “Machines > Serial” menu.

Autoscan also no longer tries to scan ports in alphabetical order; it now scans them in the same order RXTX presents them. This is closer to the behavior of older versions of ReplicatorG, and should end up scanning USB-TTY cables earlier in the process.

Have fun, and as always drop me a line or post here with any problems and I’ll do my best to fix them quickly.

(via the MakerBot Blog)

Thursday, August 06, 2009

One of my partners at MakerBot, Adam Mayer has been working non-stop on improving the firmware used to drive the 3rd generation electronics for both RepRap and MakerBot machines. New version was released yesterday:

Hey, intrepid Makerbotters! The v1.2 release of the generation 3 firmware is now available on SourceForge. This release features bugfixes and enhancements to the firmware on the both the motherboard and the extruder. You can download it here. Be sure to check the Readme.txt for installation hints! The changelog is after the cut.

There are small updates to both the firmware on the motherboard and the extruder controller. Some of the changes– like the eeprom configuration stuff– won’t be useful until ReplicatorG 0006 comes out in a day or so, but if you’re willing to experiment, I encourage folks to try out the new version, and file lots of bug reports. :)

Changes from v1.1:

* Readme.txt and Changelog.txt introduced.
* Introduction of circular buffer cursors, allowing us to easily abort processing of a command.
* Reduced blocking waits, reducing the chance of build burps.
* Added support for storing per-machine configuration data in the EEPROM.
* Support for inverting individual axes via EEPROM configuration bits.
* Better support for aborting and pausing builds.
* Stops extruder on abort.

Good luck!

(via MakerBot Blog)

Monday, August 03, 2009


RepRap, the book

Well, as many of you may know my PhD was on the mechanical considerations for Darwin (the first release of the RepRap printer). I graduated recently and have finally submitted my thesis. I've uploaded a pdf to

under the 'Machines' heading.

Please ignore the copywrite statement, this was necessary to get it submitted under university rules on time, and is in a long drawn out process of being waived.

Saturday, August 01, 2009


Battle of The Bulge pt2

For those interested, here's what can happen when you use 10mm PTFE rod for your extruder insulator with plastics that melt at a higher temperature than the original CAPA. This image shows a 3mm PLA filament extracted after a jam - the PTFE insulator is now useless. The ridges on the right are from where the thread of the screw drive forces the filament in. You can see that it fades out towards the centre indicating that at this point in the PTFE, the filament is just becoming plastic enough to conform to the walls. Only the cloudy last 6mm of the rod on the left were in the heater barrel itself, and they are only cloudy because I stress-fractured the rod at that point to get it out.

You can clearly see that a significant bulge is forming in the PTFE shortly before this, expanding the filament to nearly 4mm diameter. The PLA has very little plasticity at this point and so effectively plugs itself into any developing bulge and forces it open wider. This is why the PTFE barrel is now scrap, and may explain why some users are finding that their extruder has inexplicably developed a tendency to jam solid. This extruder had always been operated with a tight hose-clamp over the join between the PTFE insulator and the heater barrel proper.

I'm reaming out the extruder clamp/base to 16mm to take the recommended, stouter PTFE insulator that I machined up on the old new lathe (or is that new old lathe) at the Wellington MakerSpace last week. The insulator's in the suitcase somewhere...

Vik :v)

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