Dual Extruder Using a Single Motor

Anybody that has ever built or bought a 3d printer can tell you, one of the best upgrades or capabilities it can have is known as duel extrusion. Simply put, duel extrusion is the ability to use more than one material or color in a single print. This is useful when you are designing a part that has hidden internal passages that require support. Having the ability to selectively dissolve part of your print makes creating internal features easy.

The main reason for a printer not to have dual extrusion is cost. Having extra extruders comes with the unwanted side effect of a heavier tool head. More weight in the moving head means that the overall structure of the machine has to be beefed upped to handle the added inertia and this can get expensive.

One solution to this is to drive both lines of filament with the same motor and have some kind of servo mechanism change the position of the desired filament to be extruded. Others have had this idea and I can think of two working examples of it but both of them I consider to be overly complex.  

As you can see from the animation above, a single stepper motor is used to drive both lines of filament. A hobby servo controls filament tension. An important detail to note is that the stepper motors direction to advance either line of filament is the same, clockwise. The only difference is the position of the servo that dictates which filament is pressed against the drive wheel and therefore advanced. This becomes important when we start talking about machine firmware. Marlin and Repetier both come with M-code servo control support  so no firmware modification is needed. If anybody is interested in building one and would like to see the design files, let me know and I will send them. I plan on releasing this to open source when I finish it.

A look at my tool chain

I have decided to give people a look into the tool chain that I use. When I am showing somebody a part or a product that I have created, I am often asked how I made it. My typical snarky reply of  "with the power of my mind..." doesn't always satisfy the inquiring minds so I thought I would give some details. What will follow is a brief list and description of the software packages and physical manufacture process that I often use to go from an idea in my head to a part in my hand. Today, we will be building the lower bearing support for the Z axis of my 3d printer. This is the part that holds the bearing that one end of the ballscrew slides into. The bearing helps to align the ballscrew and keep it parallel to the two linear guide rods that the Z axis rides on.

 

This is a shot of the part in the design software that I use called Solidworks. At this stage, I decide how the part is going to look and how it will function. When I am satisfied that my part will do what I need it to, I save and export the file in an (*.igs) format for use in Mastercam.

 Mastercam is different than Solidworks in that here is where you specify how the part will be machined in real life. This program allows you to generate your tool paths and  select which size of end mill will be used to cut the various features of the part. This is also where the g-code is produced that the CNC mill will run. The g-code file is a list of instruction that tells mill how and when to physically move in order to cut away the unwanted material and ultimately leave you with your finished part. 

This is the part while it is being produced. The rotating end mill will follow a predetermined path that I defined in Mastercam and will remove excess stock. Normally while cutting aluminum, you would want to have some kind of coolant or lubrication flowing over the part and cutting tool in order to keep them cool and to give a better surface finish but my personal machine that you see here doesn't have that capability yet. Currently, I just spray the part with cutting oil and I get good enough results for my purposes.  I am in the process of adding an automated cooling system but that will be for another post.

The cutting finished after about 2 hours (very slow compared to a large production cnc) and the part is ready to be found among the chips.

Here is the finished part laying on top of the piece of stock it was cut from.