GBX Update Feb 22 2021

Hi everyone! Apologies for anyone who tried to join the webinar last week-- Texas had a winter storm that took out power, heating, internet, and water in many homes, including my own, and I wasn’t able to host the monthly webinar like I usually do. In lieu of it, here is a belated post of the last month of GBX R&D updates. The monthly GBX webinar will return as usual next month on Tuesday March 16th at 2PM CST.

Hopper Gantry

In last month’s update, I discussed the development of the hopper gantry, which enables more consistent material feeding by allowing the hopper to move in the x and y dimensions in tandem with the extruder. Since last month, the hopper gantry for an XLT GBX was built and validated with 80 hours of test printing. In combination with a new feed tube, material feeding has never been more consistent. The next steps are to replicate the hopper gantry on the Regular and Terabot platforms.

Feed System

In addition to the hopper gantry, the feed system was also validated by 80 hours of test printing. The new feed system consists of:

• New clear vinyl feed tube (1” ID)
• Updated feed throat that clamps onto the new feed tube
• New Hopper Feed Tube Attachment part that connects the feed tube to the hopper

The new feed tube is stronger and more rigid than the previous feed tube, which had issues with sagging and occasional tearing from wear over time. The previous feed tube was affixed at the hopper and the feed throat with a screwing mechanism with 3D printed parts, but the new feed tube is affixed with new 3D printed parts that implement a clamping mechanism, making the connection points more secure since they don’t put as much strain on the feed tube.

GBX Quickstart Guide Rev7

With the new hopper gantry and feed system, we updated the GBX Quickstart Guide with new pictures and instructions. The new Quickstart Guide (Revision 7) is available for download on our Knowledge Base.

rPLA Printing

With GBX able to consistently print longer and larger prints more reliably, my test printing hours have burned through many pounds of Ultrafuse rPET pellets, the standard pellets we use for validating the GBX hardware. Because of this, I decided to revisit re:3D’s stockpile of rPLA granulated from in-house failed prints, supports, and rafts. I had previously printed with rPLA regrind to obtain initial print settings, but I only printed small prints (NIST test artifact, dodecahedron), and with only a 0.8mm nozzle. So I loaded up a GBX with rPLA with the intention of running an overnight print.

Unfortunately, the batch of rPLA I used had contaminants that blocked up the 0.8mm nozzle and interfered with extrusion. The contaminants were white pieces of unmelted granulate, and were most likely a different plastic that we use in-house that got mixed into the rPLA. The contaminant must melt at a higher temperature than PLA (175C), so I suspect either PETG or PC.

Since there isn’t an easy way to remove the contaminant from the already granulated batch of rPLA, I simply switched to a larger 1.75mm nozzle and continued printing. With the larger nozzle size, most of the unmelted pieces of contaminant passed through the nozzle without impeding flow. The resulting print has an uneven surface texture due to the sprinkling of white contaminant, and it probably has worse mechanical properties due to the reduced print quality. But for something printed from plastic that would have otherwise gone into the trash, it’s not bad, and it demonstrates that simply increasing the nozzle size may enable the printing of contaminated plastic feedstock.