Crammer Update March 21 2024

It’s been a while since the last update on Gigabot X hardware R&D. This post will focus on active material feeding, and the last time we updated about this topic was November, 2022. A lot has changed since that post.

First of all, the active material feeder (aka “crammer”), has had a complete overhaul and is in beta testing. The first version of the crammer, described and pictured in Nov 16 2021, was fully 3D printed (except for the motor and hardware), and used a conical auger to convey and compress material. While this design worked relatively well in the short-term, internal and external testing indicated short lifespans of the printed auger and inconsistent extrusion. Additionally, the highest extrusion throughput achievable using this crammer was roughly 0.4 kg/hr (Fig. 1). Internally, re:3D is striving for throughputs of above 1 kg/hr.

Figure 1: Weighing the extrudate during free-extrusion. Uses the first version of the crammer attached to a GBX. The slope of the line is throughput, in kilograms per hour.


Taking a step back, the problems that the crammer is intended to solve are:

  1. Materials with low apparent density and low pourability (e.g. granulated water bottles) cannot flow into the GBX extruder using gravity alone. These materials tend to get stuck in the hopper or hopper tube before making it to the extruder. A result of this is inconsistent extrusion (Fig. 2B).
  2. Materials that flow well enough (i.e. high pourability) to rely on gravity for feeding, but have a low apparent density, result in a lower-than-desired extrusion throughput (Fig. 1).


Figure 2: A) The gravity-fed material path on GBX, B) the extrusion throughput of rPET pellets (apparent density of 0.66 grams per cubic centimeter) and rPET flakes (apparent density of 0.49 grams per cubic centimeter).


The redesign of the crammer followed re:3D’s new Engineering Change Request (ECR) process. The new ECR process borrows from the Mitre Systems Engineering Guide, and requires documentation of Key Performance Parameters (KPPs), Key System Attributes (KSAs) or Technical Performance Measures (TPMs). For the crammer redesign, the following metrics were established: 

Table 1: Performance metrics for the crammer redesign.

The new design is feature-packed, easy to use and maintain, and is currently in internal beta testing. The design utilizes both printed and machined parts to balance cost and longevity, however the final design might incorporate more machined parts.

Figure 3: Overview of the new crammer design.


Figure 4: Crammer beta prototype ready for testing.


The prototypes being tested now utilize a #16 stainless steel auger  (Fig. 5A) capable of feeding 16 cubic centimeters of material per revolution, which is roughly 0.5 kg/hr of flake at typical print speeds.  The auger rides in a stainless steel sleeve, which is pressed into a 3D printed trough (Fig. 5B). In the future, this trough might be fully-machined, but the current design has been working well and provides a balance of cost and performance.

Figure 5: Stainless steel auger (A), stainless steel sleeve in printed trough (B), assembled prototype crammer (C).


The current design requires only three modifications to the GBX: 1) the front extruder barrel and extruder motor covers have been redesigned to accommodate the crammer, 2) the extruder backplate will use countersunk holes and flat head cap screws rather than socket head, and 3) the Y-slide bracket has been modified to accommodate full travel in the positive X direction. See these changes in Fig. 6.

Figure 6: Required modifications to GBX in order to accommodate redesigned crammer.


The redesigned crammer has so far been used to print recycled PET flake from water bottles (Fig. 7A), and recycled PLA from failed prints (Fig. 7B). More recently (this week), re:3D printed a large wheel chock using recycled PLA. This part is 95 mm x 190 mm x 315 mm, weighed 1.4 kilograms and took over 8 hours to print, without issues with the crammer. The wheel chock print is part of re:3D’s ongoing project with the US Army.

Figure 7: Prints using the new crammer on GBX of rPET flake (A), and rPLA flake (B & C).


Most importantly, re:3D is looking for beta testers. If you would like to print with granulate using your GBX, GBX XLT, or TBX, please fill out this form


p.s. re:3D has tested 40 versions of the crammer, a very small sampling of which are shown in Fig. 8.

Figure 8: Crammer prototype graveyard

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