RepRap: Blog

No-lathe extruder interior

2009-07-02T23:47:00.004+01:00

Some were a little puzzled as to how the interior of the no-lathe extruder works. As I'm putting a few together, I took a photo showing how it combines the ideas of a simple locknut thrust bearing and a chopped-up drilled nut being used as the bearing behind the filament contact point. Files now online at http://www.thingiverse.com/thing:765.

Vik :v)

Stepper driver for Extruder Controller V2.2

2009-07-01T21:49:00.004+01:00

Zach's new extruder controller was first used to control DC-motor extruders, as used in the MakerBot Cupcake (and also older versions of RepRap). But it is also capable of driving a stepper, which will allow it to be used with the new RepRap extruder too.

You can find details on the Builder's Wiki here.

Tamiya Universal Extruder

2009-06-28T09:02:00.003+01:00

Here's a shot of the extruder designed to use the Tamiya Universal Gearbox, no lathing required. The Tamiya shaft is replaced with a 2.5mm hex key, and that fits into an M5 grub-screw locknutted on to the top of the M5 extruder drive. There is a crude thrust bearing (locknuts & washers) inside, and half a drilled M5 nut to support the drive screw where the filament presses against it. It's mechanically complete but needs wiring up with a working opto board and a thermocouple - which are in the post. Yes, I know I'll have to paint the opto vanes or stick tape on them.

So Simon, here's your new extruder :) Actually I'll tidy up the models a bit and run you off a fresh one. The modelling has been done in BRL-CAD, exported with g-stl to STL format, then repositioned with ArtOfIllusion, saved as an STL again, converted to g-code by skeinforge and then sent to the Gcode RepRap "Phoenix" by the Java GUI program. It's a convoluted path but I kept on having snags at every darned step!

With the exception of the opto-board, all the pieces were sourced in New Zealand (which bodes well for other places). One day, I'd like to stick this on an I2C control bus so everything can be controlled from an Arduino without running out of pins!

It can take either a 16mm PTFE extruder barrel or the no-lathe heatsink one as shown. The clamp fixture is compatible with Darwin interchangeable extruder holders - I checked :) I'll post the files after their final tidying.

Vik :v)

SourceForge Community Choice Awards

2009-06-24T01:02:00.003+01:00

Voting among the finalists has started! If you'd like RepRap to win the "Project most likely to change the way we do everything" category, click on the link/image above, and - of course - tell all your friends :-)

Sourceforge awards

2009-06-17T23:14:00.004+01:00

RepRap has made it to the finals of the SourceForge.net Community Choice Awards in the "Most Likely to Change the Way You Do Everything" category, so, firstly and most importantly, a big thanks to all of you who voted for the project :-)

We've done a video on RepRap for the finals, and we think it makes a good general introduction to the project too.

RepRap from Adrian Bowyer on Vimeo.

So now, when your friends who don't know the difference between the Java heap and an H bridge ask what it's all about, you can point them at that and go back to your beer...

Acceleration Code Released

2009-06-13T12:49:00.002+01:00

There is a new release of the Java host software and the Sanguino firmware that support accelerations and decelerations during building.

Accelerating RepRap from Adrian Bowyer on Vimeo.

Unfortunately the new firmware is now too big to fit in the Arduino ATMEGA 168 controllers (though the old version that does is still available, of course). However, there is plenty of room in the Sanguino, and we will be supporting the Arduino Mega as a RepRap controller soon.

The new firmware buffers all movements, and so communications with the controller are now asynchronous. This completely eliminates all pauses between one movement and the next.

The main advantage of the new code is that you can run the axis motors at much lower current (as they don't have to hit the feed-rate requested in one step from a standing start) while not compromising build times; indeed, you can set higher maximum feed-rates as the machine now accelerates up to them and decelerates down.

RepRap wins at Bath University

2009-06-12T16:27:00.001+01:00

It’s not often one gets to spring up to a podium to collect a prize, and even rarer in merely Bermuda shorts and bare feet. However, this didn’t put the judges from Bath University’s post-graduate conference from giving the RepRap project first prize.

I didn’t have to say much. When asked what was interesting about the project I said “It’s going to change the world”. She was taken aback a little, so I rammed it home: “Honest.” I said. I was then asked to summarise the work in two sentences. I looked at the ceiling for a while. “Currently we ship consumer items from the other side of the planet because we do not have the ability to make things for ourselves. The RepRap project seeks to put manufacturing power into the hands of the people by delivering a manufacturing technology which can self-replicate.”

(Poster was same from this previous post)

Tommelise 3.0 I2C board finally built

2009-06-07T03:48:00.004+01:00

In which your narrator turns designs into hardware with remarkably little trouble... Do you want to read more?

Bowden extruder success!!

2009-06-01T13:49:00.008+01:00

Wow. Finally. Four months ago I bet Adrian a Mars Bar that we could get this working, and now finally here it is – the Bowden extruder. By decoupling the motor from the carriage, we now have a ridiculously small extruder head. The implications of this with respect to machine design are wonderful: less dead space around the build volume leading to a more compact overall design, simpler carriage constraints, improved stability through elimination of moments and less energy required to move a lighter mass.

The key to this is a low-friction PTFE tube (a nod to Ian here for finding a supplier). Thanks to the archaic imperial system it is possible to get tube with an ID of 3.175 mm (1/8”) to give a nice running fit for our 3.0mm PLA filament (this is one of the few times you will witness me thanking the imperial system).

Of course hysteresis goes up as we increase the sprung length (our test used a 1 meter length to be sure). The result of this is a bit more stringy hair around the build - though Adrian’s funky acceleration code is likely to be improving matters:

Once cleaned up, we were pleased to be unable to spot the difference between builds from the first pinch-wheel extruder (back, I think) and this Bowden extruder (front, I think).

The PTFE tube can be super-glued into it’s respective housings (here ABS & PEEK) provided it is sufficiently roughed up with a file. I got my PTFE tube (1/8” ID, ¼” OD) from Adtech. I just rang Samantha there and she said if you mention the word ‘RepRap’ she might be able to sell you some without the minimum order charge.

Accelerating RepRap

2009-05-26T16:43:00.004+01:00

Accelerating RepRap from Adrian Bowyer on Vimeo.

The experimental four-dimensional GCode interpreter is now five-dimensional. Four dimensions are so three weeks ago...

It has an extra DDA variable that is the feedrate. This means that if you send it:

G1 X85.3 Y75.8 E18.3 F2495.4
G1 X85.5 Y75.5 E18.7 F2575.9

For the second move it accelerates linearly from 2495.4 mm/minute to 2575.9 mm/minute as it moves from X85.3 Y75.8 E18.3 to X85.5 Y75.5 E18.7. That is to say, it treats the F values in exactly the same way as it treats X, Y, Z, and E. (This is not how GCodes conventionally work, of course, so you can turn this behaviour off by commenting out a line in the firmware that says

#define ACCELERATION_ON

)

Of course you can have the machine move at constant speed as well if you want. You do that simply by setting the feedrate first:

G1 F2575.9
G1 X85.5 Y75.5 E18.7

That will do a move at a constant 2575.9 mm/minute, as you would expect.

The latest Java host software in the repository now supports all this (again you can turn it all off by setting Accelerating false in the preferences).

There is one final firmware upgrade needed to finish this work off: buffering the moves in the micro-controller (as Zach and co. are doing with their code). At the moment there is a barely-perceptible pause between moves, which means that accelerating to high speed hits a momentary barrier at the end of the acceleration. As the whole point of all this is to make the machine move much more smoothly, that's got to go.

Accelerations allow the machine to work faster and more accurately at much lower motor currents, or maybe even with smaller cheaper motors. Or maybe even with motors we print ourselves, which Forrest is working towards...

I2C-based Reprap control

2009-05-26T06:09:00.019+01:00

In which the control strategy for Tommelise 3.0 begins to emerge ... with implications for mainstream Arduino controllers... Do you want to read more?

Fun Night at MakerBot

2009-05-18T18:54:00.003+01:00

We've been really busy with MakerBot trying to keep up with orders and such, but sometimes we like to have fun too. Our friends Marius and Phillip from metalab in Austria are visiting for the month and they have been printing cool things ever since they got here.

Here's the video... you should definitely watch it because it's hilarious:

Small Melt Zones Look Good

2009-05-15T10:43:00.007+01:00

The difference in operation of the no-lathe extruder with different barrel lengths and a heatsink leads me to suspect that the main factor in reducing friction is to reduce the size of the zone where the plastic is actually melting.

As you can see in the photos I've chopped an old CPU heatsink (easily salvaged or made from copper/aluminium stock) into 10mm slices, and clamped a pair around the barrel. There is a recess in the middle of the two halves made with a drill 0.5mm smaller than the barrel's external diameter. I have experimented with moving it up and down the barrel. The barrel above the heatsink does nothing useful in this setup, but might be useful for guiding the filament later.

The heatsink stops the plastic melting on entry, keeping the top part of the barrel under 60C. I've rewound the heater to start the coil as close as possible to the nozzle, and to keep the windings close together. Kapton tape is great for this!

Best results definitely seem to be had with a small, powerful heater (1A@13.8V max, running at about 60%) and the heatsink placed as close as possible to the heater windings. This is much more successful than my earlier experiments with heatsinks.

The extruder works continuously, or in bursts, and I checked that it will restart after cooling. It still needs no lathe!

Vik :v)

Some notes on the way to an easy-to-make pinchwheel extruder

2009-05-15T04:47:00.013+01:00

In which your narrator experiments with ways to make Nophead's GM-17/tin can stepper hack pinchwheel extruder without a lathe... do you want to read more?

No-Lathe Extruder Pops Out

2009-05-14T03:38:00.004+01:00

I'm having difficulty stopping the barrel of the no-lathe extruder popping out. As the silicone warms up it seems to lose its grip on the barrel and the latter slowly slips out of the silicone/MDF clamp.

This combined with the extra material called for in the form of silicone tube is bringing me back closer to Forrest's and Nophead's extruder designs with long, thin-walled barrels and some form of heat-sink near the inlet.

Vik :v)

Sourceforge Award Nomination

2009-05-13T23:53:00.005+01:00

The RepRap Project is nominated for the "Project for Most Likely to Change the Way You Do Everything" category of the Sourceforge awards. If you think we're deserving of said title, click on the image and help swing the vote our way!

Vik :v)

The No-Lathe Barrel & Nozzle

2009-05-11T06:40:00.012+01:00

In true Open Source fashion, I've been distracted by the attention given to extruders without a lathe and I've figured out how to make an extruder barrel and nozzle without one too. I used some handy but unlikely pre-formed components: A telescopic radio aerial and a posidrive machine screw. To repeat the trick, you'll also need some PTFE tape, kapton tape (or fire cement), 3mm inside diameter silicone tubing, nichrome wire, nuts, bolts, and bits of MDF or similar wood product.You will need a drill that can reliably make a 1mm hole – finer if possible – for the nozzle's exit, plus the usual hand tools. The coil of wire on the right is an improvised rheostat made from the guts of my expired fan heater (thanks for expiring it, Kate).

I Started by dismantling the telescopic aerial, removing the base and very tip so I could slide all the bits apart. Find the tube that is a snug fit on an M3 or M4 posidrive machine screw. Note that one of the ends of the tube has a shoulder turned over on the end of it that stops the other bits of aerial slipping through – this will be the nozzle end. Chop off 50mm of tube and smooth the cut end.

Economic note: More tubes with shoulders can be made by cutting lengths with a a pipe-cutter and gently hammering the cut end over, allowing one to make several barrels from one aerial.

Anchor the posidrive screw in a bit of wood with a nut to make it easier to clamp or handle. Using the dimple in the top, drill 5mm into the screw. Make a 1mmm one first and try finer ones when you get the hang of it. Lubricate with thin oil or WD40 and keep the swarf clear. When you're done, clamp the screw in a vice, file of the head and make it a bit pointy so you're left with something that looks a lot like the one below (it's standing in a nut so I could take a decent picture):

Hack off the top 5mm of the screw, tidy it up, and drill a shallow 2-3mm hole on top of the small hole you exposed with said hacking. You should now have something like a little grub screw with a hole through it. Why not put a hole through a grub screw? 'Cos I got no M3 or M4 grub screws. That is your nozzle.

So wrap the little beast with PTFE tape and pop it down the barrel that you cut off the aerial pointy end first. It should wedge itself in the shoulder at the other end. If you push too hard you'll deform the barrel and pop the thing out the other end. Bad move.

Insulate with kapton tape, add 6-7 ohms of nichrome wire near the nozzle, insulate again. That's your heater.

Slip 10mm of a 25mm length of 3mm ID silicone tube over the open end of the barrel and clamp it all in MDF. I found it necessary to add an MDF slip over the top part of the silicone tube later on to stop the soft plastic bulging within the tube. I used bolts to connect up the power to the nichrome and kapton-taped a thermistor probe to the side. The combination works well up to about 180C with PLA and is stable at temperatures of up to 300C by which time the PLA starts coming out as smoke rings. Surprisingly, the silicone stops the MDF from burning.

So there you have it. Easy to get bits, easy to make, no lathing.

4D Printing

2009-05-07T20:38:00.006+01:00

Wot? Another coat hook? So what's new here?

The fact that it was printed in four dimensions, that's what. I've upgraded the Java host software and the Arduino/Sanguino G-code firmware so that the system treats the filament length to be extruded in each movement as another independent movement variable, like X, Y, and Z (as proposed here; you've got to have a stepper-driven extruder - like the pinch-wheel extruder - for this to work).

That is to say, the DDA in the firmware, which previously generated straight lines in (X, Y, Z) space, now generates straight lines in (X, Y, Z, E) space, where E is the growing length of extrudate needed.

From the outside, this means that everything works exactly as before. So why bother? The reason is that it makes it a lot easier to do tricks like accelerating and decelerating the extrude head as it moves, which means that it can both go faster and run on less current. This will be the next thing that I do.

I've done a new release of the host software in the repository available here, and written an upgrade to the Arduino/Sanguino firmware called FourD_GCode_Interpreter available here. To turn on 4-dimensional behaviour, simply set the flag FourD=true in the reprap.preferences file. Set it false to make the machine work as it did before.

Perhaps surprisingly, the firmware doesn't need to know if it is being driven in 4D mode or 3D mode. Lines in the G-code now look like:

G1 X23.9 Y39.0 Z0.2526 E66.5 F3000.0 ;print segment G1 X23.9 Y39.7 Z0.2526 E67.2 F3000.0 ;print segment

So, for example, the second line is saying move 0.7mm in Y from where you last were and extrude 0.7mm of filament while doing so, all at 3000 mm/minute. But if you leave the Es out and turn the extruder on and off separately, everything works just as before (so old G-code files will still work). You can still control the extrude rate separately too - just set the extruder to go at a different speed to the carriage, and everything comes out right automatically.

Unsurprisingly in retrospect, this taught me something about the control of the stepper which drives a pinch-wheel extruder: you don't want to turn the current off between plotted segments. If you do, the stored spring energy in the compressed filament and the pressure in the melt chamber cause the stepper to slip back (as no current is flowing to hold it) at the end of one line segment and before the start of the next, resulting in a poor-quality build. The new firmware turns the current on when the extruder is first used, and leaves it on until the temperature is set to cool. The latter is a bit of a hack (and we could easily add a "current off" M-code instead), but in practice it works very well. The resulting build quality is excellent.

One final thing: I have only tried the firmware in the Sanguino, and not the Arduino. I can see no reason why the latter shouldn't work, though. Let me know...

Taking the Gm-17 out of Nophead's GM-17/tin can stepper hack

2009-05-05T17:09:00.004+01:00

Reducing the vitamin content of the Mk I Nutjob extruder... do you want to read more?

Stovetop recycling of HDPE swarf

2009-05-03T16:53:00.005+01:00

In which your narrator solves the problem of recycling plastic scrap, for milling... do you want to read more?

Documenting the Mk I Nutjob

2009-05-03T06:36:00.016+01:00

Nophead: This looks really promising, but I am having trouble understanding the physical arrangement from the photos. Any chance of a view from underneath, or a diagram?

Forrest: Absolutely... do you want to see more?

A different approach to extrusion

2009-04-30T05:30:00.009+01:00

In which your narrator goes nuts... do you want to read more?

Introducting the RepRap Motherboard v1.x

2009-04-29T19:39:00.004+01:00

This is another board that has been in development for quite a while that I have done a pretty sad job of communicating to the community about. Well, it's now ready for primetime and a bunch of people have been using them for a while.

The idea on this board is to consolidate the stepper control onto a single board, give it a comms network to control modular 'slave' devices which can control extruders, etc, and also to give it an SD card slot as well as some other cool features. It's based off the Sanguino design.

Anyway, I summed it up much better in the wiki page:

This board is the brains behind the Generation 3 Electronics. The heart is a Sanguino which is an Arduino-compatible board that is powered by an ATMEGA644P chip. It has connectors to hook up all the various peripherals that you'll need to drive a RepRap machine. It has headers for three stepper drivers, as well as 4 RJ45 connectors for Extruder Controller Boards. Not only that, but it has an SD card and a connector to hook it up to an ATX power supply.

Some highlights:

* Onboard atmega644p - 64K flash space, 4k ram, 32 I/O pins, Arduino compatible.
* 3 x Stepper driver connectors with min/max inputs.
* Built-in SD card socket for printing from file and buffering large print jobs.
* RS485 connection for noise-free communications with extruder / toolhead controllers.
* ATX power connector for power. It can also turn the power supply on and off.
* Headers to allow existing Sanguinos to plug straight in.
* I2C headers for simple hookup of external peripherals.
* On/Off switch for instant-kill and simple control of the entire system.

This board was developed by the RRRF and is available for sale from MakerBot Industries as a kit. They will also be available fully assembled in a month or so.

DIY chip fab

2009-04-29T13:44:00.004+01:00

This blog is for RepRap progress, but sometimes things happen elsewhere that deserve a mention too.

So, thanks to Julian Skidmore for telling us about Jeri Ellsworth, who is doing amazing stuff...

Check out these two links to her work:

http://www.flickr.com/photos/jeriellsworth/2835524263

and

http://www.flickr.com/photos/jeriellsworth/2835459827

Skeinforge Support

2009-04-23T18:49:00.004+01:00

I've been trying out the support material in Skeinforge and said I'd post some pictures. The settings have not been fine tuned but I'm still very pleased with the results. The object was a simple test shape it is 100mm tall and 30mmØ the columns are 8mm x 2.5mm and the column length is 75mm. So quite a delicate shape.

Skeinforge generated a good support structure and it printed OK with our firmware the head goes to a rest position every time the temp changes so it did this approx 500 times (twice every layer) as the support went down at 235°C and the Print at 250°C this in turn lead to lots of hairs coming from the print. I resisted removing them during the print and wanted to know if it would work with Zero intervention, it did :-)

The print took about 1/2 hour to clean up and the support was better stuck than I would have liked, in removing it I broke the columns, this was a little upsetting up until the point I realised I could glue it back together and the join was invisible and as strong as the rest of the model, I also figured that it was not an unacceptable solution as the end result is a very acceptable print (well I think so for zero tuning).

Ian www.bitsfrombytes.com