Several of our local SOLID Learning educators recently gathered to evaluate microcontroller options for the robotic designs. During a break, discussion of ongoing cutbacks for supplies was a topic of some interest – one teacher mentioned a proprietary system that requires cartridges for thermal printing that cost almost $30 USD for each 6oz cartridge. He had found a generic source for the fluid that cost less that a single cartridge per gallon but was having problems recharging the cartridges.
Each cartridge had a very narrow opening that was longer than the needleless syringe he had available, so he asked if I could design and print a custom funnel for him. He provided some basic measurements and I was able to create a 3D model using a CAD application and then print out the sample funnel during the session.
Unfortunately, the initial funnel was too small but we were able to test it over the next break and a better fit was designed for the second test print. A longer extension allowed the second design to fit into the cartridge but this revealed a second barrier installed to defeat re-loading attempts – a small cup held against the inner port of the cartridge by small elastic connectors effectively closed the flat funnel tip even when inserted fully, preventing reloading using the second design.
I was able to adjust the design and create a variation of the funnel that would push the cap out of the way but vent the fluid through four holes directly constructed into the 3D printable object. Using this simple device with a larger fill cup, the proprietary cartridges can now be refilled for a fraction of the cost using generic fluid and a 3D printed funnel. If the funnel is ever lost, another one can be easily fabricated using the same STL file on any available 3D printer.
The first model was printed in black ABS, but PLA proved more resistant to the fluid’s solvent properties. The later versions were fabricated by the MakerBot using 1.75mm purple PLA filament. It might have taken three tries to produce a working solution, but each version expanded the capabilities of its predecessor and required only minor adjustments in the CAD file to create the next version of the STL model that could be shared with others through services like Thingiverse.
Using a few cents’ worth of plastic and electricity, the teacher can now fill a cartridge roughly 20 times for the same price as a single proprietary cartridge using generic supplies – sustainable and inexpensive for a few minutes’ work with a CAD program.