How it works
When we have already a CNC machine and want to be able to use it as a 3D printer like RepRap, we just need to add the plastic extruder and his controller to the CNC. The 3 motor axes of the CNC will be controlled as normal by EMC2 and the same normal hardware controllers.
When we convert the STL files to GCODE files using Skeinforge, Skeinforge will produces some special GCODE like M100, M101 to control the extruder, along with the normal G1 movement code.
Now, it is crucial to understand the differences between two systems to see why this is a favorable RepStrap setup, especially if you own a CNC mill already. And what the differences are, and how we can close the gap.
Mechanically, they are both consists of a 3-Axis motor driven platform. While CNC Mill has a motor spindle for milling, the RepRap has a plastic extrusion motor and a nozzle temperature readout device. So by converting a Desktop CNC mill, the 3-Axis platform (the most complicated part) can be reused.
As both system are controlled by GCode, the whole 3-Axis platform system as well as its electronics and logical signal can usually be totally reused.
We need to overcome the following differences to convert the CNC Mill to a RepStrap.
A standard RepRap takes the GCode from SD Card or Serial Port, parsed and decoded in the RepRap Motherboard. The motherboard then control the 3-Axis bot directly, and the Extruder indirectly through the Extruder Controller by communicating over RS-485 and some internal protocol. The motor and heater control logic resides in the Extruder Controller.
A standard CNC Mill controlled by EMC2 takes the GCode from a file, parsed and decoded in the computer. Then the 3-Axis bot is controlled by some kind of hardware driver. The most common desktop CNC setup being the Stepper driver through parallel port. However, EMC2 has no knowledge about the temperature and extruder GCode command extended by RepRap team.
- Filter scripts are created to transform the output of Skeinforge to something understandable by the EMC2.
Parallel port device is being the most common hardware interface for a typical EMC2 setup. However, it lacks of the ability to read the temperature input - something that requires Digital-Analog Conversion.
Also, there might not be enough leftover hardware pin to control the extrusion motor - be it a stepper motor, or DC Motor with Encoder.
- Reuse the standard Extruder Controller controller for the missing hardware interface we needed. A special firmware and EMC2's userspace driver script has to be built for that.
- Script which redirects and parse the extended GCode, and communicate with the aforementioned driver.
Note: If you have the hardware (like interfacing card) providing all the additional input and output needed, you could interface the EMC2 directly to the extrusion motor, the heat element and temperature read-out. Potentially, you could translate the extrusion and temperature command as another "virtual" axis, and hook them up with the PID loop in the EMC2, just like how you treat a normal axis. EMC2 comes even-better-than-RepRap algorithm and processing power to handle all these.
The Wiki here focus on the most common scenario, that's it:
- You own a Desktop CNC Mill, already usable with EMC2.
- You interface it with the Parallel Port. And that's the only low level hardware interface your computer has.
So the solutions mentioned above applies, and the material here should be able to walk you through. Please be aware that this implies:
- You still need to obtain a Extruder Controller. But not the Motherboard as EMC2 replaces 100% of its role.
- You still need the actual extruder, like Motor, Barrel, Nozzle and such..., and be able to replace your Mill's spindle with this.
These are out of the scope of this document.
NOTE: This guide follows the work of sam0737 user.
End to End Story
- Keep your 3-Axis bot setup, including the limit switches.
- Remove the spindle component and connections.
- Hook up the Extruder Controller board. Connect 12V power to it.
- Connect the Extruder Controller to the computer's serial port, usually through a Arduino compatible USB->TTL programmer cable.
How to print?
- Export the object as STL file from the 3D authoring software
- Use Skeinforge to convert the STL to GCODE
- Print the GCODE with EMC2
Here is a list of active developers/users:
- Sam Wong (from China) shared his code files for EMCRepStrap on 2009. Contacts: Website and e-mail: sam-at-hellosam.net
- Casainho (from Portugal) started to build his EMCRepStrap following the steps of Sam Wong and with his help. Contacts: Website and e-mail: casainho-at-gmail.com
If you are going through this route, of course you will need a CNC machine. EBay (and Taobao for China) is a good source for cheap CNC machines.