Thursday, January 13, 2011


RepRap MicroExtruder

I have started to design a MicroExtruder for 1.8mm filament.  So far I have just got the non-reprapped parts, shown above.

As you can see, it is about the size of the two end joints of my index finger.

It is a miniaturised version of my standard extruder here, which was based on ideas from Nophead and others, with bits from me.

From the top there is the filament (green - thanks Vik!)  then a length of 8mm diameter PTFE.  This screws into the brass nozzle with an M6 thread.  There is then a PEEK disc with two 2mm holes either side.  Those will take two M2-threaded rods.  The tension in these will resist the extrude pressure.

The brass nozzle is threaded M4, and screws into a small brass heater block.  This takes the normal RepRap thermistor for temperature measurement, and is heated by an 8.2 ohm metal-film resistor rated up to 235 oC, which should give 16 watts at 12 volts.

The filament hole down the PTFE and brass is 2mm in diameter.

So far it is untested - watch this space...

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I used the term "microextruder" too for a filament drive system I've been working on. This is designed to be used with a planetary gear stepper, but I plan to design a printable gearbox to optionally replace that.

This design is also untested, because I wasn't able to get it to print because, as I later discovered, my Huxley's X carriage was totally FUBAR. Unfortunately, I hadn't printed a spare because I was trying to redesign that part, and the prototypes that I had printed softened and became unusable when I tried to install a hot-end.
Could you please justify why do you want to add 1.8mm filament option to RepRap while 3mm option is working and tested? -- what are the advantages and disadvantages?
Where do you get 1.8mm filament?
Sounds like a cool idea for high-resolution printing.
Be careful when using PTFE; especially if you are a smoker. Ensure you have good ventilation to get rid of the fumes from the melting PTFE. Breathing the fumes from melting PTFE often cause Polymer Fume Fever. I worked with a fellow who was a smoker and did PTFE "hot-air welding" who was hospitalized after such an incident.
Refer to the sixth paragraph under Polymer Fume Fever at
I'm happy to relinquish the name microextruder if you want. Or, equally if you want, we can use it collectively for a class of extruders - your call.

The smaller the filament diameter the lower the extrusion force (the pressure is constant), therefore the smaller the motor needed and the less the gearing. Plus Vik gave us a sample of 1.8 PLA filament and his supplier can easily produce it.

PTFE is fine up to 250 C and we only need 200 for PLA. It doesn't melt till 330 C (though it will start to degrade before then). Note that 200C is cooking oil smoke temperature, at which the world does an awful lot of frying in PTFE-coated pans...
For a given flow rate and nozzle aperture the size of the motor needed stays the same I think, just the gearing changes.

I managed to extrude with this tiny motor at a very high feed rate. The only problem is that with a high gear ratio you cant reverse as fast.

The main benefit is less force where the teeth meet the plastic so you can apply more force and get a higher pressure.
@Adrian I wasn't saying that. There's no reason we can't both use the term, I just wanted to point you toward it in case it gives you any ideas. We'll probably end up with a couple of extruders in this class anyway, just like we have the "Wade's" and "Adrian" geared extruders.

The Brutstruder (using a DC gearmotor and the makerbot naming convention of using "-struder" as a suffix) is arguably the first member of this class (though I had an explicit design goal of making mine smaller), and Makergear has a compact hot-end assembly designed to be used with a version of it modified to accept the same type of planetary gear stepper I have.

With 1.7-1.8mm filament, you can probably direct-drive the filament with a worm gear on a stepper. See this take-apart of the UP! extruder for an example. The Makerbot Mk5 gear with 6mm bore can be considered an off-the-shelf part, and ebay user raysyu sells compatible bronze gears (with teeth that look even better than Makerbot's) for a couple of different shaft sizes. Right now, I only see an 8mm for the planetary gear stepper or M8 bolt, an M4 threaded hole for the Adrian geared extruder, and an M6 to match the Makerbot version (this one is apparently being discontinued), but he has also previously had one with a 5mm bore suitable for a NEMA 17/14 shaft.
"the motor needed stays the same I think"

Nop - You're basing that on the fact that it must be delivering the same power, yes?

I agree that must be so. But power = torque x revs. Assuming the same gearing for the moment, torque is about half because of filament cross sectional area, but the filament needs to move twice as fast. That means that a lower torque (=smaller) motor being clocked faster should do the trick.

Or have I missed something?

I like the take-apart of the UP extruder (not least because it's so clearly based on all of our collective work - imitation is the sincerest form of flattery etc...)

For the drive I'm thinking of hobbing an M6 bolt with an M4 tap. Rhys tells me that others have found that using too small a tap for this doesn't work well, so I'll make a shallow M4 indentation. I'll probably drive it with a locked wing nut, as on my old extruder, rather than the nut's head.
Yes but you can always use a smaller motor spinning faster with a higher gear ratio, as I illustrated with a tiny motor and 3mm filament. Using smaller filament is just like increasing the gear ratio.

You do get that extra gear ratio for free though, so a given set of gears, yes you can use a smaller motor going faster.

There are two other considerations though when choosing the motor and gear ratio. How fast you can reverse and how much one step of the motor equates to in extruded filament.
New Image is making 1.7 mm filament these days. It's a bit more expensive per pound than 3 mm because, I'm told, he has to keep a man with a hand on the machine at all times. With 3 mm you can go to lunch leaving the filament extruder running by itself. :-)
Well this microExtruder can open the way for a multiExtruder Reprap...
@Marcus, I sell 1.75mm PLA in spools & rolls, assorted colours. I do ABS as well, but PLA is much more environmentally friendly.
hi i am new to all this and could really use some advice I just got an up dated version of the rip-rap Mendel printed parts a full set of electronics the fibre board cut panels and hardware set with belts . I still need motors and extruder head heating set up but I find myself confused on what to get in these any help will be greatly appreciated . redwolf2008
hi i am new to all this and could really use some advice I just got an up dated version of the rip-rap Mendel printed parts a full set of electronics the fibre board cut panels and hardware set with belts . I still need motors and extruder head heating set up but I find myself confused on what to get in these any help will be greatly appreciated . redwolf2008
This comment has been removed by a blog administrator.
Hi redwolf2008

Email me ( and I'll do my best to help.

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