Plastruder MK5

Warning

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The plastruder contains certain parts that can be dangerous if used in an improper manner. The extruder tip can become hot. (>250 celsius) There is also a 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.

Many of the images here show the Plastruder MK5 without ceramic tape for illustrative purposes. Always use ceramic insulating tape. Not only does it keep the temperatures stable and conserve energy, it also keeps your fingers safe from burning!

Overview

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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.

Filament Drive System

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The MK5 uses a 'Paxtruder' style filament drive system. This system uses a fixed DC motor with a drive gear on the shaft. The plastic is pressed against the drive gear by a smooth plastic plunger made from Delrin. The depth of the plunger is adjusted with a thumb screw. This system for filament extrusion is robust and simple to use. Changing the filament is simple and does not require any sort of tools. To remove the filament, loosen the thumb screw and pull the filament out. To load new filament, insert the filament and tighten the thumb screw. This takes so little time to do, that it is even possible to change filament mid-print.

The thumb screw also eliminates the need for a measuring stick. Simply tighten the thumb screw to the desired strength and you're done. If it is not tight enough, you can tighten it during operation without any problems. You will soon quickly grow to love the simplicity of the system and wonder how anyone ever dealt with idler wheel issues in the past. The plunger is made from Delrin, which is a high strength, low friction plastic that can handle thousands of hours of operation. In our extensive testing we noticed minimal wear on the plunger. If the plunger does eventually wear, you can simply tighten the thumb wheel slightly.

The drive gear itself is a custom part machined from 303 stainless steel. It is much stronger than the previous idler wheel, and the new drive gear geometry results in a much higher push strength. We did extensive testing and were able to generate push forces of up to 180N. We documented this process pretty extensively on our blog here and here.

Hot End

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The hot end on the MK5 has been completely overhauled. It is now almost completely failure proof and is capable of running for hundreds of hours (and counting) before any sort of maintenance is required. It is also much easier to work with. Many of the difficult parts such as heaters and temperature sensors now simply bolt onto the assembly.

This new hot end completely solves the 'PTFE Bulge' problem of the MK3 / MK4 plastruder design. Instead of relying on the mechanical strength of PTFE at high temperatures, the new design uses stainless steel for the structural components. The nozzle, thermal core, and thermal barrier tube are all made from 303 stainless. The filament is guided all the way though to the nozzle through a tube of PTFE plastic. This PTFE plastic is backed by steel the entire way, with no chance for deformation. The steel provides a robust structural support while the PTFE provides an extremely low friction path to the extrusion zone. Furthermore, the PTFE tubing is an off the shelf component that can be quickly and easily replaced if it should ever wear out.

We've also redesigned the heating system. Instead of custom, failure prone nichrome wire, we now use off the shelf power resistors. These power resistors simply bolt onto the side of the thermal core and can be connected by soldering or quick connect fittings. They are available from a wide variety of manufacturers, and come with a 1% tolerance rating. This means that every MK5 hot end will be almost identical and that the settings will be more universal.

Since controlling the temperature of the extrusion head is extremely important, we are transitioning to the use of thermocouples. The MK5 thermal core has a tapped hole on the side which can be used to attach a thermocouple. For those users that are still using thermistors, it is a simple matter of taping your existing thermocouple to the same spot. The MK5 has a higher thermal mass. The benefit of this is that the temperature is generally more stable. The downside is that the heater needs more power, and it takes a bit longer for the extruder to heat up to operating temperatures.

Last, but not least we have reworked the nozzle. The nozzle now screws into the thermal core instead of the other way around. The threading on the nozzle has been changed to a standard 3/8"-24 thread pitch which allows for easy hacking and custom nozzles. The nozzle is now made from 303 stainless steel which is much stronger and more corrosion resistant than the brass nozzles on the MK4 design.

Get One!

Gathering all the parts for building one of these can be pretty time-consuming. For some parts, you have to buy a large amount of something (like machined parts) 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 MK5 kit from the MakerBot Store.

Assembly

Building the extruder takes about 2 hours from start to finish. It's a pretty straight-forward process where you bolt together parts, 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.

Assembly instructions.

Usage

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.

Usage instructions.

Source Code

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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:

* Thingiverse - download the source, talk about it, etc.
* Google Code - download the release.
* Subversion - direct link to the MK5 release tag.

Unless otherwise stated, the content of this page is licensed under GNU Free Documentation License.