Dual Extrusion Cupcake - ABS Plastic & Silicone

Winter Project #1: Dual Extrusion Cupcake

So, I needed a simple, hackable platform to explore 3D printing of 2 or more materials. I was particularly interested in combinations that involved a thermoplastic such as ABS, PLA, etc... and other non-thermoplastic materials such as RTV silicone, wood filler, etc...  I happened to have a MBI Cupcake CNC lying around; I had replaced it with a far better printer years ago. The Cupcake CNC was my first 3D printer that I had built, so I was quite familiar with the strengths and weaknesses of the Cupcake CNC. So, I modified it. It is better for it to be used in the name of research than to be gathering dust.

The non-thermoplastic materials that I was focused on could be dispensed with a air extruder similar to MBI's Frostruder MK2 or a motorized plunger system such as FAB@HOME uses. I decided to go with the air extruder because of it's simplicity and minimization of hysteresis.

I really didn't like MBI's Frostruder MK2, it seemed overly complicated. I did not understand the reasoning for the air solenoids on the Z platform with the extruder held in a more complex package than needed to be......after all this is 3D printing, something can be printed that holds a syringe barrel quite easily. So, I moved the solenoids(I tried finding a 3/2 solenoid, so I wouldn't need 2 solenoids but I had a hard time finding one in 12V for a reasonable price) to the upper left side of the Cupcake. This freed up some room on the Z-platform and I designed and printed a nice syringe barrel holder that mounts in front of the MBI MK5 plastic extruder. This syringe barrel holder eventually evolved into a toolhead holder(more on this in later posts) and after a couple of iterations I had something that I was confident would work. Next, was the electrical work.

I  used RepG's M106 and M107  M-codes to cycle the Fan output of Gen3 mainboard. That fan output was the signal that would be used tell the air extruder to pressurize or vent. Now, I only had one output, the fan, on the Gen3 mainboard to control two air solenoids. Therefore, I made a custom air extruder controller out of an Arduino Uno that would controller the solenoids depending on the output state of the fan pin. In keeping with my motto of trying to keep extraneous portions of the design off of the Z platform, I mounted on the left side of the makerbot. Ah... now the software.

Fig 1: Modified dual extrusion Cupcake

Using RepG's G54, G55, etc... g-code offsets made coding the tool offset easy. I made some quick python scripts for a object 25mm X 25 X 8mm tall that would combine my to two g-code files, one for the thermoplastic and the other for the second material, together. So, now I had a single file I could run and print with. The python scripts that generated the g-code made it easy to characterize and optimize the dispensing of the the material from the air extruder.

Now the really test, dual extrusion of ABS plastic and silicone.

Fig 2: Silicone calibration and initial ABS + Silicone prints

Fig3: Calibrating Silicone and ABS extrusions




Fig 4: Success! On the left is a completed one without the silicone being fully enclosed and the one on the right  with the silicone being fully encased by ABS plastic.

So, by the end of it all I had printed ABS and silicone within a single print.  After all this time,the Cupcake was definitely showing it's limitations and it boils down to how much more time and money(mainly time) do I want to put into the Cupcake to get it printing to "modern" resolutions, if that is even possible. Also, the build size in the Y direction is reduced by 35mm due to the tool offset and  thus reducing the Y direction build envelope by 35%. I have had my Cupcake for over 3 years; several generations of new low cost printers have come and gone within that time span with better hardware and better software & workflows. Now, hope is not lost for the Cupcake... remember that I created a toolhead holder. So, other toolheads could be mounted and I have a couple of different ideas that could be used on that. However, I have a MakerGear M2 on its way so I can further explore dual extrusion(shhhhhh.... maybe even tri, quad, etc... extrusion too.)

Now, I need to package up all the files and post it to thingiverse.