GBX Update November 16, 2021

Hi everyone! Here are the GBX R&D updates from the past month:


HID Global rPC Flake Testing

In the past month, material testing was conducted on recycled polycarbonate (rPC) flake from HID Global. The flake was granulated in re:3D’s SHINI granulator from ID badge manufacturing waste produced by HID Global from their Austin, Texas headquarters.

The HID Global rPC was previously tested with older hardware configurations of Gigabot X, including the extruder body, feed throat, and feed tube. Previous testing revealed issues with inconsistent flow of the flake into the extruder. Since then, the inlet hole into the extruder body was doubled in height, and the feed throat was updated for smoother material flow and to interface with the new inlet hole.

However, these improvements were not enough to overcome the flow issues of the rPC flake. During a test print, the extrusion rate gradually decreased and underextruded. 

The next step to addressing the feed flow issues was testing the HID Global rPC flake with the Crammer, which is a motorized auger screw system that actively conveys materials into the Gigabot X extruder. Testing with the HID Global rPC flake informed some design changes to the Crammer screw, which is described in more detail in the next section of this post. Printing with the updated Crammer mitigated the feed flow issues, but extrusion was still inconsistent throughout the part, resulting in failed layers and varying perimeter widths.

The extrusion inconsistency would occur several minutes into printing the part. During troubleshooting, the crammer was removed from the extruder, revealing compacted flake at the inlet that prevented flow into the extruder. After dislodging the compacted flake and restarting the print, the extrusion rate would return back to normal before eventually underextruding due to compacting flake at the inlet.

The Crammer motor’s movements are synchronized with the pellet extruder motor via ditto printing, or Marlin’s Dual Nozzle Duplication Mode. However, our Marlin version does not have a mechanism to finely control the rate of the Crammer motor RPM in relation to the pellet extruder motor, since the Dual Nozzle Duplication Mode was originally intended for printing with two extruders with the same extruder motor. Ideally, a gcode command would set the relative RPM rate of the Crammer motor to optimize the Crammer RPM per material, preventing both compacting and underfeeding.


Crammer Design Updates

The Crammer, or Active Feeding System, is a 3D printed feed throat with a motorized auger screw that conveys material into the Gigabot X extruder. The Crammer was developed for use with print materials that have difficulty flowing into the Gigabot X extruder, namely regrind with irregularly size flake like rPET water bottle flake, or TPU pellets or regrind, which have a tacky texture that makes the particles stick together and not flow well. 

In the past month, design updates have been made to the Crammer Feed Throat Rev11 to further integrate it into the Gigabot X printer. Changes include:

  • Updating the clamp mechanism for attaching to the feed tube
  • Extending the top of the Crammer feed throat to match the standard feed throat
  • Adding wire holders for wire management
  • Adjust geometry for mounting to the extruder body

Crammer Feed Throat Rev11 was used in combination with Crammer Screw Rev8 to conduct material testing on recycled PET water bottle flake. The material testing established the maximum extrusion rate at 0.38kg/hr.

The same feed throat and screw assembly was used to conduct material testing recycled polycarbonate (rPC) flake from HID Global. During testing to establish the maximum extrusion speed, and therefore the maximum extrusion rate, the crammer motor began skipping, capping out at a maximum extrusion rate of 0.13 kg/h. This is significantly lower than the 0.38kg/hr achieved with the rPET flake.

To investigate, the crammer was removed from the extruder. Gcode was sent to the Gigabot X via USB through Simplify3D’s Machine Control Panel to turn the extruder motor. The skipping continued even with the feed inlet cleared. The rPC flakes were compacting further down the screw, where the diameter of the crammer feed throat decreases. The hypothesis is that the rPC flake cannot be compressed as much as the rPET flake.

To mitigate compacting of the rPC flake, the Crammer Screw Rev8 was revised to Rev10 to include the following changes:

  • Decrease screw length from 3.8” to 3.2”
  • Decrease depth of thread from 0.2” to 1.5”
  • Adjust the geometry for better interfacing with the crammer motor shaft

With the new hardware changes, material testing was conducted again on the HID Global rPC flake. The new maximum extrusion rate was 0.38kg/hr, and the limiting factor was the pellet extruder motor reaching its maximum torque, and not the crammer motor.


GBX Knowledge Base Articles

To address common questions from recent Gigabot X support tickets and training sessions, the below articles were created or updated on re:3D’s Knowledge Base:


GBX Firmware

GBX firmware 4.2.4 has completed a 3 month testing period, and is now ready for release. Access the GBX 4.2.4 Reg firmware here. Other build sizes will be published soon.

GBX firmware 4.2.4 includes the following updates since 4.2.3:

  • Bug fixes for purge routine
  • Menu changes
  • Adjusted extruder numbering from 1/2/3 to 0/1/2
  • Setup for crammer usage
  • Adjusted build volume
  • Optimized acceleration and jerk settings
  • Addition of Terabot X custom files


Exabot X

Exabot X is under construction! David has been hard at work installing a pellet extruder on Gigabot X. Exabot X firmware has also been adapted from both Exabot and Gigabot X firmware, and uploaded to the machine. The next steps include:

  • Testing the firmware, including obtaining the final build volume dimensions
  • Rigging the vacuum feed system
  • Developing a combination feed throat, reservoir hopper, and proximity sensor holder to integrate the pellet extruder into the automatic vacuum feed system


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