Twin Extruders for Fisher?

Have just taken this snapshot from the STEP file int he github repository for Fisher. Looks like someone was experimenting with feeding two strands of filament into the extruder head? I can only assume that this would need the first to be retracted for the second to pass into the nozzle, and there would have to be a small squirt to clear any residue of the first filament before starting to print the second colour. Looks interesting but way beyone me to impliment, it would need to be coded into the software to deal with the two extruders, plus the added complication of two Bowden tubes, another extruder motor, two spools etc. May be a little too complicated for a Fisher.

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geeksarebeta
Have just taken this snapshot from the STEP file int he github repository for Fisher. Looks like someone was experimenting with feeding two strands of filament into the extruder head? I can only assume that this would need the first to be retracted for the second to pass into the nozzle, and there would have to be a small squirt to clear any residue of the first filament before starting to print the second colour. Looks interesting but way beyone me to impliment, it would need to be coded into the software to deal with the two extruders, plus the added complication of two Bowden tubes, another extruder motor, two spools etc. May be a little too complicated for a Fisher.

looks awesome though, and would def need the duet 0.8.5.

There are some photos on Twitter of them testing it.

We did a lot of testing of this, but unfortunately it was very difficult to get it to work reliably, and most of the problem was down to swapping the filament. There's a couple of ways to do the swap; either you leave the hot end hot, retract filament a short distance to allow the next filament past, then extrude enough to clear the filament left in the nozzle, or you cool the hot end down to around 90C, retract the filament far enough to pull the filament right out to the bottom of the hot end, then feed in the second filament.

However, neither works perfectly. If you don't cool the hot end down, the filament withdraws with a string. This can be enough to block the filament coming in. There's also the problem of how much to purge from the nozzle, to make the colour change. We used Cura for slicing when doing this, as it provides a 'dump' tower when changing tools. If you cool the hot end down, and pull out the 'plug' of filament from the nozzle, there's much less priming of the nozzle, but feeding the 'plug' from the nozzle out, and then back in again, is also not reliable. A lot of this depends on having good filament, and a good filament path. Feel free to experiment with it!

The alternative is to have both filaments primed at the nozzle, though this generally means having a custom nozzle. E3D have the 'Cyclops' hot end for mixing two filaments. However, it feels rather over-engineered. RichRap did a nice bespoke nozzle that would mix two filaments, but again, it was custom-made, and limited to two filaments. We were hoping our solution would scale up, so you could swap between any number of filaments (which these other options can't do), rather than be limited, but ultimately, we couldn't get two working reliably.

Actually mixing filaments to have a range of colours is a different ball game entirely, and really needs an active mixer, to mix filament together, otherwise the extrusion tends to come out like toothpaste, ie with stripes of the individual colours!

You don't have to use the 0.85 Duet; the standard 0.6 Duet can support the Duet Shield or Duex extension boards, for more extruders and tools.

Ian