Thursday, July 25, 2013


ShopBot Desktop as a 3D Printer for Sugar Glass

Hi, So for Bioengineering research I've been looking for a way to improve precision and reproducibility of each print with a bit less consideration on cost (this is for working with human cells eventually, safety and sterility are more important than cost). The main constraint is I need it to be able to print sugar glass and use my BariCUDA extruder, which means the extruder mount needs to support a few pounds without having any problems.

Kliment in #reprap suggested I modify a ShopBot Desktop, and so that's exactly what we did. With awesome help from Gordon at ShopBot and Johnny at Ultimachine, we were able to get things going. Also, MAJOR props to Erik Zalm who maintains Marlin firmware for helping us get everything going. NOTE: BARICUDA is now a #define in Marlin so you can turn on/off sugar printing functionality on your RAMBo with a simple switch. Thanks again Erik!

We took out the brains of the ShopBot, left the gecko stepper drivers, replaced the brains with a RAMBo board from Ultimachine. We used the motor ext pins on the RAMBo board that we then sent the step and direction pulses to, and fed them directly into the stepper drivers using a modified 37 pin connector. My modified Marlin Firmware is available here: Here's the setup and some more details in the first video:

The ShopBot is all acme rod for movement, and it can drive the motors very fast because the large motors (NEMA 34?) are held at 48 V. So you don't lose steps. It's still open loop motion control, but it has been awesome. This RepStrap has been fantastic for sugar printing and it is being used every day in the lab at UPenn.

Now that I am setting up a new lab at Rice University in Houston TX, I am very excited to get another one! Forward SCIENCE! Did I mention you should contact me if you want to come do a Sabbatical? We need more specialized repraps for Bioengineering. More on that next month. :D

Here's the final video printing sugar glass on a ShopBot Desktop:

I used a RAMPS to interface external drivers, using custom made DIP-like carriers to wire the 5V, pulse, direction & enable signals to the external drivers. The only necessary alteration to the firmware is to invert the enable signal.
nice. i could not find it documented anywhere. i had to alter the firmware to send the step and direction signals to the motor-ext pins. also to control pneumatic extrusion of molten sugar. now these mods are available in trunk and in my repo.
By the way, that sugar glass print was successful... See this video to see what the object actually is:
3D Printed blood vessel networks
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