Printing with dual extruders adds another level of complexity to 3d printing. The newest versions of most popular slicers have incorporated dual extruding into their software and for the most part made it a relatively easy affair to extrude plastic from two separate extruders and make a decent looking 3d print. Just like most things in 3d printing your results might vary depending on the 3d printer, slicer and materials you print on. I have recently discovered a small trick that made the dual color 3d printed SGR logo above turn out a bit nicer with one small change.
If you study the two prints in the photos you will notice that the print on the right is much cleaner. The yellow portion of the print has very little bleeding/oozing coming from the black portions. Often when printing a part like this you would use an ooze shield, but the part on the right was printed without an ooze shield. If you know what an ooze shield is and what it is used for skip the next paragraph.
Oozing is a common problem with FDM 3d printers. For an FDM 3d printer to work it has to heat the plastic to its melting point where the plastic can flow freely from the nozzle onto the printed part and bed. Oozing is a common side effect of an FDM 3d printer nozzle when it sits idle and has heated plastic in the nozzle. This oozing can cause your prints to have poor surface finish. With dual extruder 3d printing with two separate nozzles, like I use on the MakerGear M2, one nozzle is heated and idle while the other is printing so that it can switch seamlessly between the two. A common solution to protect the part from ooze is aptly named an ooze shield. Ooze shields serve two purposes during printing. First they create a protective and temporary shield around the part so that ooze from the idle nozzle can't get stuck to the printed part and secondly they allow the on deck nozzle a chance to extrude a bit of fresh filament to make up for the material lost during oozing. While a bit wasteful ooze shields can be a useful solution when you want a clean dual color 3d print.
But the part on the right was printed without an ooze shield. The part on the left was printed first and I was unhappy with the print for a few reasons. So I tried reprinting the part angled on the print bed at approximately 30 degrees. I did this to solve another issue but it had another positive side effect.
Notice the slight angle of the print above.
Angling the print changed the orientation of the printers nozzles in relation to the printed part. The original orientation from the print on the left (the messier one) allowed both nozzles to be parallel with the part during the print. This meant the idle nozzle spent most of its time above the print while the other nozzle was printing. Any ooze or smeared plastic on the idle nozzle would get spread around on the part while the other nozzle was printing.
By angling the part this changed the orientation of the nozzles in relation to the printed part. With the part angled the idle extruder was now off the part and not smearing its ooze into the part. This created a much cleaner print without the use of an ooze shield. The same benefit could be achieved by angling the part up to 90 degrees. Obviously this benefit would be diminished or completely eliminated if you were printing a wider part. But for two color signs like the SGR logo this works great.
Finally to compensate for the lost material due to the oozing be sure to use a prime pillar. Prime pillars allow the printer to prime a small amount of material out of the nozzle during the tool change.
The BCN3D Simga 3d printer solves this problem by separating the two nozzles entirely. Each nozzle moves independently of the other and parks over off the part while the other is printing. While I have not had the pleasure of using the Sigma I have heard good things and seen excellent dual color 3d prints from it.
I learned several things printing this model. Initially I would have wanted to print this part laying down flat on the bed, as this would be the fastest to print. However I wanted to film a time lapse of this part being made. With the MakerGear M2 the Y axis moves which means the only (simple) orientation to get a smooth time lapse is to attach the camera to the printers bed. So I built the part standing up. After learning the above trick with angling the part I now realize that laying the part flat on the bed would have been even worse for smearing of the two colors. In the flat orientation the idle extruder spends an even longer time over the part.
While printing standing up in the Z for a thin sign/logo takes a while longer excellent results can be had by simply re-orienting the part in relation to the XY axis.