Multi Colour Printing without using wipe or prime towers
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I think a solution would be to have two gcode buffers reading from the file. One would be in advance of the other and its function would be only to count the filament extruded and look out for tool change or mix change commands. At each such command it would subtract the purge length from the filament extruded to give the point at which the change needs to be made, and store that in a queue along with details of the tool change or mix change command. The second gcode buffer would do the actual printing and look out for when the filament extruded reaches the amount given at the head of the queue.
RRF is already able to segment moves, because it has to do that when applying grid based bed compensation to moves that are longer than the grid spacing. So splitting a move in two to do a tool or mix change in the middle wouldn't be a problem.
I'm not sure we would have enough free RAM on the Duet 0.6/0.8.5 to implement this, but we would on the Duet WiFi.
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A couple of things. This method isn't perfect. For one thing, there is no allowance for the transition between one filament and the next. In practice, at least with the Diamond hot end, the transition is so small that it is hardly noticeable. Other hot end designs may have larger or more active mixing chambers which might mean that the transition between one colour and the next would be noticeable. The other thing that will screw it up is if there are insufficient moves between tool changes to fully purge the filament. The object would need to some pretty small coloured sections for this to be a problem but it's possible.
So I'm thinking that there may well be a requirement for some sort of very small wipe or prime mechanism in conjunction with what I've done so far. I'm planning to see if I can build something in which will generate some sort of a small purge mechanism (but nothing as large and wasteful as a full wipe/prime tower).
Note that these issues only become apparent when changing colours within the same layer and where that layer is visible on the finished print. If the colour change happens at the layer change boundary, then it's just a matter of setting the slicer to give 2 or more perimeters and to do the inner one(s) before the outer one.
Ian
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While this can be done in Firmware as David suggests, is it not better done by the slicer for the reasons Ian points out?
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I guess if it's easy enough enough to implement "look ahead" tool changing in firmware, then it would be a good thing to do and it might well suffice for many situations. There is probably no single best solution but perhaps a combination of firmware and some additional post slicing / pre-print processing may be the way to go. In any case, I'll keep trying to develop the post processing route because it may be helpful to RepRappers who aren't using Duet firmware.
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… The other thing that will screw it up is if there are insufficient moves between tool changes to fully purge the filament. The object would need to some pretty small coloured sections for this to be a problem but it's possible.
I don't see why a short sequence of moves in a colour before changing the colour again would be a problem. It just means that there may be more than one tool change in the pipeline.
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… The other thing that will screw it up is if there are insufficient moves between tool changes to fully purge the filament. The object would need to some pretty small coloured sections for this to be a problem but it's possible.
I don't see why a short sequence of moves in a colour before changing the colour again would be a problem. It just means that there may be more than one tool change in the pipeline.
What I mean is that if the amount of filament to be extruded between colour changes is less than the amount needed to purge out the old, then extra purging "off print" will be needed (I think - but maybe not). Say for example you were to print a face and the eyes alone were in a different colour to anything else, and those eyes only needed (say) 4mm of filament but 5mm was needed to purge out the old. I guess all the filament for the eyes plus part of the next colour would be held in the "purge zone" of the hot end. Maybe it would work. Dunno, I'll test that scenario when I get chance.
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Say for example you were to print a face and the eyes alone were in a different colour to anything else, and those eyes only needed (say) 4mm of filament but 5mm was needed to purge out the old. I guess all the filament for the eyes plus part of the next colour would be held in the "purge zone" of the hot end. Maybe it would work. Dunno, I'll test that scenario when I get chance.
That's what I had in mind. Treat the melt zone and nozzle as a pipeline. Your scheme relies on the approximation that the colour mix that goes into the melt zone comes out of the nozzle a fixed distance (i.e. length of filament) later. You may have more than one colour change in the pipeline.
Let me know how well this scheme works out so I can decide whether/when to implement it in firmware.
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Yes I'll do some more testing/refinement and get back to you. Not sure when that will be as my wife recently had surgery so I'm having to be chief cook and bottle washer (and cleaner, carer etc).
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Clever idea Deckingman, I like it.
One more complication I noticed. Different filaments need different purge lengths. For instance when I am switching from black to white, I need to purge a hell of a lot more than when going from green to blue, for instance.
No idea if that is the case with all hot ends, not having a Diamond I can't test it.
Also, how is this with different types of filaments? Is ABS easier or worse than PLA, for instance. -
Hi Lykle (yasoo file mou)
No problem with different coloured filaments on the Diamond - can't really see why different colours of the same filament would need different purge lengths. I suspect the purge length you need for Black to White is correct and using less with Green/Blue probably means that they aren't fully purged but you can get away with it because a bit of Blue mixed in with Green probably doesn't show up. Funnily enough, I've just finished a door sign for my Hairdresser (well it got me a free haircut), not Black and White but Black and Silver (that's what the filament is called but it's light grey in fact). I used the same purge setting as the Union Jack. It's not perfect - there is a bit of Black round one of the screw holes which shouldn't be there) but it's not far out. Here is a link https://youtu.be/naiLL9qYeTE.
Maybe something weird happens with different dyes but I've not yet come across that problem. Having said that, I have only done limited testing so far and it's early days.
Can't comment on filaments other than PLA. I can't think of any logical reason why the same method wouldn't work though.
Ian
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Yasou!
OK, so the Diamond head is definitely a different beast than my lowly V6 lite.
Good to know. I should try and upgrade but way to busy at the moment.If you want to try out different filaments that feel completely saturated with colour, you should try nGen. It feels as if you are printing colour particles instead of plastic. Their white even gives the impression of being "chalky". It isn't but that is what it feels like.
(btw, was thinking of designing a very compact 3 filament Nimble, good idea?)
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Yasou Lykle,
Purging during tool change with a mixing hot end is a lot different to purging out a single filament to be replaced with another. I think that's maybe led to a bit of misunderstanding. For sure, when you want to change one filament for another it takes quite a lot to purge all trace of the old filament out of the hot end. But when you switch from one loaded filament to another, you only need to purge the small bit of filament that is in the mixing chamber and from the mixing chamber to the nozzle tip. I was quite surprised myself when I started testing on how little this actually is. For example, when loading a new filament I'll extrude 50mm or more before the new colour is complete;y clean of all traces of the old. However, when switching between one loaded filament and another, it takes only around 2.5mm. From observation, the "transition" between one filament and the other is I'd guess only about 10% of that so around 0.25mm which in most cases is hardly noticeable. Of course, other "multi input" hot ends might have larger mixing chambers and need more purging, so there may still be a need for some sort of small sacrificial "tower" if there is a large transition period between filament changes. The Diamond doesn't really have much of a mixing chamber - it's about 2mm long. This is both an advantage and a disadvantage in that the filament doesn't actually get mixed but rather, comes out like stripey toothpaste.
Not sure how a 3 filament nimble would work. You need to drive each filament independently and feed each one to a different heat sink/input on the hot end.
Ian
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Clear.
Wonder if changing the position of the filament feed holes will change the stripey aspect. Doubt it. Will probably need a screw in nozzle option to make real mixing an option. Looking at the corkscrew shapes they force plastics through to mix properly, it might be a bit too big.
3 filament Nimble. Just a small block that holds 3 complete Nimble mechanisms. But the idea is a bit silly as it will be just 3 extruders coupled to the hot ends with bowden tubes. Only advantage is that the extruder block is very small. OK enough about this.
One more thing on the color changing. Just a comment on the cleverness of the people here.
1 you thought of it and tried it.
2 David and Tony took one look and realised what you are doing.clever.
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Clear.
One more thing on the color changing. Just a comment on the cleverness of the people here.
1 you thought of it and tried it.
2 David and Tony took one look and realised what you are doing.clever.
Thanks - I'll take that as a compliment. As an ex automotive engineer, self taught in writing code and everything else, currently scratching a living by cutting and screwing bits of wood together, and too many years the wrong side of 60, I need all the encouragement I can get.
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Ian
I have just ordered a Diamond Hotend for the CoreXY Build that I intend to resurrect after Xmas so may well be chasing you for configs etc when the time comes
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Ian
I have just ordered a Diamond Hotend for the CoreXY Build that I intend to resurrect after Xmas so may well be chasing you for configs etc when the time comes
Any time Doug - you know my email address. I've got my machine pretty well dialled in. Of course, if there is info you need that might benefit others, then post here and I'll reply here.
Ian
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So as promised, herewith a link to the new blog that I have set up, in which I have created a post giving full details of my technique. The information should all be clear but if you have any questions, feel free to comment on the blog and I'll do what I can to help. https://somei3deas.wordpress.com/blog/
Please bear in mind that I only set the site up a couple of days ago and I've gone with the free WordPress plan which means I am very limited in what I can do with the design and layout. Also, apart from a brief introductory post, this is the first post I have ever made so I have much to learn.
Be warned that I'm not a programmer and if you use the Python Script which I have linked to, and it crashes your PC, don't blame me. Having said that, it works fine for me.
I give this information freely in the hope that others may benefit from my endeavours. If you find it useful, then a word of thanks or attribution would make an old man very happy.
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It would be cool to have some kind of color/transparency sensor that could determine if the filament has reached the correct spot in the tool chain. Not sure what good that would actually do, but sounds fun.
Jeff
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@(In)Sanity:
It would be cool to have some kind of color/transparency sensor that could determine if the filament has reached the correct spot in the tool chain. Not sure what good that would actually do, but sounds fun.
Jeff
I have no idea what that means or how it could help. Each of the filaments are loaded into the hot end as far as they can go which is the point where they all come together in the "mixing chamber". They have to be. If there is any gap, filament from one of the other inputs will be forced back up into it. So the distance from the end of the filament where it enters the hot end, to the nozzle tip is a fixed amount which never changes. Why would you need any sort of sensor?
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So picture a sensor that can detect if the nozzle has reached a purity level and then can skip steps on the priming tower to not waste as much plastic, The next prime would just bridge if needed. This could allow variable priming. Such a sensor would be incredibly hard to accomplish short of a focused camera, or passing light through the filament. I have a Cyclops myself and so far I'm happy with it.
Yah I know this has nothing to do with your approach.
Jeff
