I must start by stating that this is not my idea, I saw something similar fitted to a 3D printer several years back and have just made my own version adapted to the UP2! 3D printer I am currently using.
The printer is not mine (it's on loan from a friend) and it was only supplied with a roll of white ABS. I made another instructable and one of my wishes was that I had some different colours for each of the components in order to show them off a bit better.
Step 1: The Concept
You can also dye ABS after manufacture with acetone and Rit dye, this however is a messy process and your component turns out all one colour.
Sharpies use a solvent called ethylene glycol monobutyl ether (say that with your mouth full!) and this acts in a similar way to the acetone in that it eats into the ABS and carries with it the colour of the marker.
The great thing about this method is that sharpies come in a massive range of colours and ink finishes, also as the sharpie is only friction fitted, you can pause your print part way through and change to a new colour. With my unit you can even insert 2 sharpies, both the same for a stronger colour or different colours to create a mix.
Step 2: Design
The component was drawn up in Fusion 360.
I started by measuring the top of the print carriage, I then oversized the Base of the print to hang over each side, this stops slippage. I was not worried about latching or fixing the dye head down as the print material runs downwards (so pulling the tool) and I didn't want to damage or permanently modify my friends printer.
I located a 4mm diameter hole for the print material to pass through.
I then created two drawing planes at 45 degrees to the center line of the hole.
I measured a sharpie with my calipers and found that it was 10.7mm in diameter and the shoulder to the tip was 37mm. I should point out here that I am using fine sharpies, not ultra fine.
All 3 holes intersect, this means that the ABS has to run across the tip of the marker and carry the colour into the extrusion head.
I must again note that I made the mistake of assuming that all sharpies are made to an exact diameter and have found that some are a little more...plump! These ones need a quick touch of some sandpaper to make it to the end of the holder.
Step 3: Printing and Test Fit
I exported the design to a .stl file (included below) and printed it on the UP2!
I allowed the system to autoplace and set he resolution to .2mm per layer and the infill to medium density as I wanted something quite strong.
The print took 1 hr 43mins and consumed 19g of ABS.
Once I removed the component and cleaned off the support material I did a test fit of the markers as shown in the images.
When you look into the hole for the ABS you can see the chisels of both markers.
Step 4: Fitting to the Printer
I had a very similar tube material so I cut this to length to guide the ABS into the hole but the tube stops short of the markers allowing the ABS to rub off some colour.
I pressed extrude a few times and changed the marker colour between to see that the ink was transferring.
Once I was happy that the process was working it was time for a full test.
Step 5: Extrusion Test Result
I retried with the pink and purple markers and you can see the coloured extrusion on the left in the image.
I wanted to make a full print to test how the colour developed over a large area but when I started the print I found that the markers needed to be tensioned just right to balance between colouring the filament and allowing the filament to flow though as required.
You can see the raft in the top right of the last image tinted but I had to stop to allow the print to run smoothly.
I don't have time to tweak the tension as this printer is borrowed and has to be returned tomorrow, the item on the printer is for my last 3D print instructable (unless I win one in the 3D printing competition that is).
If you get a chance to make one please feed back here as I would love to see the final effect in the glory of a full print.