Using two filaments through one hot end

Hi, guys. I would like to print finished items in two colours rather than glue items together.

As I can see there are three options:

  1. Swap the hot end part way through the print and hope that I get the alignment right and do it fast enough to keep the print hot (not going to happen).
  2. Fit two hot ends to the machine (one at 25% x axis and one at 75% x axis), note the distance between them etc. and accept that I lose 50% of my print area (would work but reduces the print area).
  3. Modify the hot end to accept two filaments (solves all the problems above but can it be done?).
    So the thought is that I create a hot end that can accept two different filaments (the same material, different colours). It would have two filament drives that feed to the extrusion head via opposing slow radii (probably through a water cooled pre-head). When the colour needed to be changed the code would be modified to move away from the print, retract the currently used filament so that it cleared the point that the feed radii intersected. The new filament would then be fed into the extrusion head (a pause will probably be required to heat/preheat the filament). The head would then be purged and return to the print.

So my question is assuming:
I can drive a second filament feed motor.
I can design a two filament feed arrangement and keep the filament cool enough to pass the point at which the two feed radii intersect to provide pressure to the extrusion head.
Would the filament that is being extracted withdraw cleanly enough to not interfere with the new filament and then be in a condition that it could be fed again later in the print (or next print) when required?

I would expect some ‘tail’ on the withdrawn filament but hopefully this would be hot enough to be drawn back into the heated section by the new filament and ultimately disconnect only becoming a purge issue.
The dangers are (as I see them) the ‘tail’ jams the new filament feed and the retracted filament cannot be feed back to the heated section when required.
If this has been done and I have missed the post please let me know.
By the same token, if I’ve lost the plot totally let me know.

You know the E3D Cyclopse?

I just know this “ready to use” Model and its still not released. Keeping this in mind, i think it will be a big challenge to build it yourself.
The “Tail” is no problem. You just use a “prime pillar”. Kind of a hollow Cylinder next to your printing object where the noozle primes and extract the “wrong” colour before printing with your second colour. I don’t think its necessary to say that this kind of dual extrusion wastes more filament than using two colours with two seperate extruders.
You may reconsider a two extruder setup. The noozles are build very close to each other. Less than 30mm, often less than that. It won’t reduce your printing area just a little, maybe nothing at all.

If talking E3D, why not consider one of these Chimera or even kraken parts?
I saw someone who fixed the kraken on the K8200 recently in the forum.

I have printed with 3 to 4 different colors with the K8200.
You have to baby sit it though.
In the software at the top there is a pause button.
When you get to the layer you want to change colors press pause.
Then move the bed with the manual controls so you project is not under the print head.
Raise the extruder 20mm put a sheet of paper under the print head.
Press the button turn motors off.
Do not bump the bed!
Turn the large gear on the extruder a couple of times.
Now unload the plastic and reload the next color.
Again turn the large gear a bunch of times to clear the extruder of the first color.
The plastic will collect on the paper for easy clean up.
Move the paper out of the way
Next lower the extruder 20mm.
This is the hard part with a pair of tweezers clear the nozzle of any plastic that is coming out.
Click on continue printing while making sure the nozzle is clear.
The printer should go back to where it left off and continue printing.

Hope this helps.

Hi, guys. Thanks for the quick and concise responses.

Cantax: I hadn’t seen the cyclops – it’s very much along the lines I was thinking. Looking at their design it’s a ‘u’ shape that would require a second filament to be present in order to maintain pressure at the nozzle. On the plus side you could do colour mixing with this, but on the down side I feel that some of the ‘currently used filament’ may tend over time to creep up the sides of the ‘none used filament’ and cool possibly causing a jam.
I was thinking of using a ‘y’ shape with the heat on the lower single leg of the ‘y’ and the filament retracting to the upper cooled leg.

I suspect that because of the nature of pressure and the fact that there has to be clearance between the filament and it’s guide that creep upwards occurs on all hot ends, but is counteracted by being drawn back down to the nozzle by the filament it is creeping past and doesn’t cause a problem.

Ichbinsnur: Again I hadn’t seen these – I can see the idea of separate hot ends reuses proven methods and doesn’t lose too much of the print area.

Wrong Way: Your post got me thinking. On relatively simple colour prints (e.g. a mug in your football team’s colours (Edit: don’t ask me why I thought of that as an example)) if you drew the first colour and converted to g code it would estimate the length of filament required (you may be ahead of me at this point), then draw the second colour convert; again you get a filament length. So you could create a custom filament by cutting up the appropriate lengths of colours required and sticking them together (method of your choice hot knife, heat gun, cigarette lighter) trim the join back and spool it back onto the drum and print as normal through a single head. Whilst this is not going to produce the most accurate of colour changes throughout the print, I suspect it would be accurate enough for many prints with a zero cost and the potential to use an unlimited number of colours.

Anyway that’s given me lots to think about.

Thanks all.

If you look in Repetier Gcode editor (after you slice it) and have the 3D view and Show layer range selected you can step through it and find what layer you want to do the color change at.
Like I said you have to baby sit the machine but (to me) it’s worth it.

I thought about splicing it too but could not get it smooth enough to go through the Teflon tube and did not want to mess my machine up.

I’ll see if I can post a picture of one of my prints tomorrow.