The lead picture is four, two color coasters all printed together. One does not have to look too close to notice there is no change color purge tower. 

I really like the complexity and color blend in this design. So I decided to print four-at-a-time before I made a filament color change. Oh, yeah, that and also just because I could.

If you are not familiar with single nozzle multi-filament (and color) FDM printing, A purge tower is a structure on the build plate where the printhead travels to figuratively “blow its nose” when changing colors. 


The original color is printed out on the purge tower by the new color pushing it out of the nozzle. The new color is printed long enough to be certain the original color is fully cleared. Then the printhead returns to the main print to run the new color.

The purge tower contains as many layers as the main model as the tower must maintain the same layer height as the main model. There is not yet a FDM printer with a linear 3D printhead "Z" movement within a single later except for an optional incremental rise “hop” in a travel move when moving to a new printing location within a layer. With the CNC machining world it's termed 2-1/2 Dimension machining. The part made is 3D but the Z movement is in incremental steps.

Even when there is no color change a new layer must be added to the purge tower to keep it the same height as the main print.

Technically a 3D move to a shorter height purge tower is possible but requires much more complex programming and worse, probably more time as a “Z” move to a new set height is usually quite slow. Also the print head must avoid hitting the main model at all times.

I can also imagine a “dump bucket” that maintains Z print height. The nozzle travels to the bucket, does a free-air purge into the bucket and the filament “dangle” gets wiped off on the trip back. Again, much too complex. I have seen a form of this with IDEX dual head 3D printers when the unused head is parked.

Here is an important point:

Printing with no purge tower is not possible and not desired with every type of two color print. When it can be used as shown here, it works very well. A purge tower with this four coaster print would only be as high as the coasters with a material cost less than three cents. The time required might have added 15-20 minutes to the print time. Not that much in a seven and a half hour print job. There is a purge going on here, but it is so small it is contained in the fill area of the model. It's called a "shadow" purge.

A much taller print using the ability to print without the purge tower becomes much more tangible in time and material saved.

Some prints require a purge tower to create the cleanest color change. Time and material cost are not important. Quality is job one.

The reason this type of purge works well with Cetus2 is it has a very special single nozzle that has a very short purge volume between filaments.

Another print option is to build the purge tower as part of the model structure and it become concealed within the model. Cetus2 permits this and it has worked well for me. Again, it does not apply to every model and every print. It’s another workable option for producing clean color change with a single nozzle.

As a final note:

IMG 1428All the dual nozzle dual color printers generally require either a purge tower or a shell wall around the model to “wipe the drooling filament from the approaching new nozzle” that leaked out while it was waiting off on the sideline to come back to the action. 

This single nozzle no purge tower is one if not THE cleanest processes for 2 color FDM printing.

Post notę: Cetus2 can also do OTF (On The Fly) color switching (no purge) on vase and single layer modes when appropriate and desired.

Cetus2 two does not offer the perfect single way to print two colors. It offers many workable options instead of one-way fits all.