Plastruder MK4

Good to Know

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The Extruder contains certain parts that could be dangerous if used in an improper manner. The extruder tip can become extremely hot. (>250 celsius) There is also an extremely powerful motor that can pinch fingers. Make sure you always run the extruder fully assembled and that you never touch the hot metal tip. Always keep the extruder away from flammable objects and never leave it hot unless you are actively printing.


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The Plastruder is the 'print head' for your MakerBot. You can think of it as a souped-up, robotic hot glue gun. Its main purpose in life is to heat up the plastic you feed it, and then extrude it out in a fine stream that you can build with. It has two main parts: the filament drive mechanism, and the heater barrel assembly. The filament drive mechanism is the part that grips the plastic and pushes it into the heater for extrusion. The heater barrel assembly is the hot part of the extruder that melts the filament. It also has a small diameter nozzle where the hot plastic is forced out.


  • Accepts 3mm plastic filament
  • Maximum extrusion rate: 16mm/second
  • Maximum temperature: 260C

Usable Plastics

  • ABS - recommended polymer. cheap, ubiquitous, low shrinkage, strong objects. ABS == Acrylonitrile butadiene styrene.
  • PLA - excellent polymer. made from corn, transparent, eco-friendly, biocompatible and biodegradable in the body. PLA == Polylactic acid.
  • HDPE - cheap polymer. very smooth, relatively high shrinkage factor. HDPE == High density polyethylene.
  • CAPA - fairly expensive polymer. very low melting point. low friction. CAPA, aka PCL == Polycaprolactone.

Get one!

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Gathering all the parts for building one of these can be pretty time-consuming. Also, you have to buy a large amount of something (like Nichrome) when all you need is small amount. Not only that, but buying a kit from the creators supports us so we can make it better. That's why we offer a kit that contains everything you need to build one yourself.

You may buy a Plastruder MK4 kit from the MakerBot Store.


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Building the extruder takes about 2 hours from start to finish. It's a pretty straight-forward process where you bolt together parts, use tape, cut and solder wires, and other fairly simple tasks. We've simplified the extruder design so that it only requires simple, common tools to assemble. If you have a partner or friend to help you out, it will be much more fun.

View the assembly instructions here.


Your finished extruder is a robust, solid device for extrusion. If you treat it properly, it will extrude for a long time. There are certain things you should know about your extruder in order to avoid damaging it.

1. Never run the motor without extruder being hot.
2. Never feed in a second strand of filament.
3. Always turn off extruder when you are done printing.
4. Double check the target temperature before extruding.
5. Never let your filament run all the way into the extruder.

View the usage instructions here.

Source Code


The design of this extruder is 100% open source. What this means is that we've released all the CAD files used for parts and the documentation under free licenses. The majority of the files are DXF files created by QCad. There are a few different ways you can access the files:

Tuning and troubleshooting.

There are a number of things that can be adjusted and tuned to get a plastruder to work just right.

Top of the plastruder!

  • Filing the hole - Early machines didn't let you tighten the wheel close enough for the filament to get a strong grip. The fix is to file the hole for the M8 bolt that holds the retainer wheel.
  • Tensioning - Check the pressure on the filament with the 2mm measuring stick. If you don't have one, you can try the flat sides of a hex key for an m3 nut (about 2.5mm)
  • Floss the teeth - Plastic can build up between the teeth on the plastruder drive pulley which results in an innefective grip on the filament. Take the motor out and use a needle to scrape the plastic out.

Bottom of the plastruder

  • Small thermistor- (A "small" thermistor is 1mm (1/25") or smaller in diameter; a "large" thermistor is around 3mm (1/10"). The small thermistor is different and requires that you either raise the temps to from 220 to 235 in the raft section of skeinforge, or update your extruder board firmware after changing the values in ArduinoSlaveExtruder/ThermistorTable.cpp accordingly. (see this thread for more info.) New — you can now upload the v1.8 extruder firmware and adjust the thermistor settings directly from ReplicatorG. See our page on adjusting the thermistor settings.
  • Check the resistance of the nichrome wire. It should be 6 ohms. You'll need a multimeter for this. A lot of people skip this step when building their machine and regret it later.
  • Check placement of the thermistor, it should be very close to the tip of the nozzle.
  • Continuity check. Check the nichrome wire and see if it's burned through it's protective sleeve and is grounding out.
  • Make sure your using some heavy duty wire for the connection from the nichrome wire to the board, otherwise it will heat up too and cause problems! One pair of twisted pair ethernet seems to work nicely.

Next step: Cupcake Board and Cable Installation for batch 1-9
Cupcake Electronics Installation for batch 10-

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