RUG/Pennsylvania/State College/Paste extruder

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Overview

Paste extruder overview

The ability to print pastes, and not only plastics, opens a door to many new objects: ceramic pastes can be used to make buildings, chocolate or sugar can be used to print food. The first paste extruder we made was using a motor and a belt to push the plunger of a syringe containing the paste. Even though we were able to print basic objects with this kind of extruder, it rapidly shows its limits since retraction isn’t possible (thus creating leaking problems). We switched to pressurized gas based systems to improve the extrusion. The extruder described on this page is compatible with OHM carriages, therefore all the other components (mechanical axis, electronics) of the printer can be kept. See the OHM page for more information (Ohm).




Components

Here is the list of the non-printable components required to build a paste extruder. Refer to the component name if the web link is broken.

Name Quantity Link Price
Air compressor (100 PSI) 1 http://www.harborfreight.com/1-3-hp-3-gallon-100-psi-oilless-air-compressor-97080.html $62.99
Air compressor's hose 1 http://www.harborfreight.com/20-piece-air-compressor-starter-kit-68191.html $12.99
Air compressor's hose to nylon hose adapter 1 http://www.wicvalve.com/Male-Connector-Tube-OD-1-8-X-NPT-1-4-Air-Instant-Fitting-PMC-T1-8-N1-4.htm $0.94
Solenoid valve (12 V) 1 per extruding syringe http://www.wicvalve.com/1-8-Inch-3-Way-Pneumatic-Electric-directional-Solenoid-Valve-3AK-1-8-G.htm $16.76
Solenoid valve to nylon hose adapter 3 per extruding syringe http://www.wicvalve.com/Male-Connector-Tube-OD-1-8-X-NPT-1-8-Quick-Release-Fitting-PMC-T1-8-N1-8.htm $0.94
Nylon hose to syringe adapter (10cc) 1 per extruding syringe http://www.dispensinglink.com/10cc%20syringes.htm Not on website, ask for the price catalogue ([email protected] glink.com)
Plastic syringe (10cc, luer-lock) 1 per extruding syringe http://www.dispensinglink.com/luer_lock.htm Not on website, ask for the price catalogue ([email protected] glink.com)
Nylon hose 1 http://www.grainger.com/product/NYCOIL-Tubing-2VDL5 $10.37

Syringe holder

The syringe holder uses the same X-Carriage as the Open Hybrid Mendel (OHM X-Carriage). The .STL file can be downloaded here: Paste-extruder.zip.








Assembling

Mechanics

Syringe holder on an X-carriage

Assembling the syringe holder is pretty straight forward: once all the components are printed, put them together with M3 and M4 screws. Use Nyloc nuts to make sure that the screws will remain tightened.





Pneumatics

Pneumatic components graph
Pneumatic components photo

To assemble the pneumatic circuit:

  • Screw the air compressor's hose (yellow) to the air compressor. Wrap the male thread in teflon tape to guarantee sealing.
  • Screw the other end of the air compressor's hose to the nylon hose adapter.
  • Screw all three solenoid valve to nylon hose adapters.
  • Cut the nylon hose to pieces of the right length, and plug them (see the photo).
  • Add a stopper on the last solenoid valve. You can make one by bending the nylon hose and holding it with a zip tie.
  • Plug the solenoid valve to the fan port on the Ramps board or RAMBo.















Generating the gcode and printing

Slic3r (http://slic3r.org) can slice a CAD file into G-code for the paste extruder. It requires specific settings:

  • Go to Preferences and turn Slic3r into expert mode
  • Print settings:
    • Layers and perimeters:
      • Set the layer height to the right value (this value depends on the paste, and must be determined through experimentation)
      • Set first layer height to 100%
    • Speed:
      • In the set for print moves sub-section, all the values should be identical, and equal to the printing speed determined through experimentation (it depends on the paste, the nozzle and the pressure)
      • The speed for non-printing moves can be left to its default value
      • Set the first layer speed to 100%
    • Output options
      • Download the perl script to turn extrusion commands into fan commands (Paste-perl.zip), and place it in any folder (don't forget to un-zip it). Then add its absolute path to the post-processing frame. On Unix, open the terminal and run the command "chmod 755 /path/to/the/script". Make sure that there aren't any white-spaces in the script's path (it may result in a crash). On Windows, you need to download and install a Perl interpreter: http://www.perl.org.
    • Advanced:
      • Set the first layer to 100%
  • Filament settings:
    • Cooling:
      • Disable both options (fan always on and auto cooling)
  • Printer settings:
    • General:
      • Set the G-code flavor to MakerWare (MakerBot)
    • Extruder 1:
      • Set the nozzle diameter to the right value (this value depends on the paste, and must be determined through experimentation)
      • Set the retraction length to 2 (disabling it provokes a bug)

The post-processing script used turns the extruding commands into fan commands. If you plug the solenoid valve on the fan port, you won't need to re-flash the printer. Note that if you don't re-flash it, since there is a temperature security, you must left the regular extruder's thermocouple or thermistor plugged (considering that you took a working printer and replaced the extruder).

In order to determine the right values (this hasn't been done yet, and must be followed with caution):

  • The layer height is close to the height of a printed paste line.
  • The nozzle size shouldn't be set to the actual nozzle size, but rather to the printed paste line width.
  • The speed depends on the nozzle size, the viscosity of the paste and the air pressure. Try to find values that result in a good print for these 4 parameters (including speed).