Multi Colour Printing without using wipe or prime towers
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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
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After a bit more testing, I've made a bit of a discovery. I'm not 100% sure but it seems that the required "purge amount" needed to find the optimum tool change position is inconsistent, and that this inconsistency may be related to print speed. I've put a bit more detail in my blog https://somei3deas.wordpress.com/2017/01/16/update-to-blog-6th-jan-printing-without-wipe-and-prime-towers/
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This is a copy and paste of something that I have just posted on the reprap forums.
If my theory is right, then if the speed of filament through the extruder is constant the amount needed to purge the hot end will be constant. What I think is happening is that the melt zone effectively expands and contracts inversely proportional to speed of filament through the extruder, so the amount of filament needed to purge also changes. There is probably a time element in this as well. This is something that I had observed at the start of every print where there seemed to be "bleeding" of colours after printing the perimeters to purge each tool and then starting the print proper. i.e the first tool change or two. I thought it was an error in my script but I'm now leaning towards the theory that it is due to the long heat soak that the hot end is subject to while it is warming up which effectively increases the melt zone. This can easily be overcome buy increasing the purge amount for the first tool change or two but I need to do more testing to determine how much by.
The difficulty arises when there are significant changes to print speed, for example the fist layer is usually printed more slowly so more filament will need to be purged than for other layers. Having said that, it won't be a huge problem if some of the inner layers are slightly out, as long as the outer perimeters and visible surfaces are correct. What is obvious though is that if the "purge amount" is optimised for an object printed at 80mm/sec, then it won't work for another object printed at 40mm/sec. It is possible to get the correct purge amount for any object by trial and error but it would be nice to have an algorithm that calculates it automatically. So, I need to do a lot more testing to determine the relationship between extruder speed and purge amount required.
The thing that will really balls this up is that if the user changes the print speed after the script has been run and during a print. In which case, the purge amount needs to be dynamically variable in "real time" depending on extrusion speed and that could only be achieved through firmware and not by a static "pre-print" script. (are you listening dc42?) winking smiley
In the end, it may be that a small wipe of prime "tower" or mechanism is still required but it won't need to be anything like as large.
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Ian
Sounds like you are really getting into the details. My idea for working this out is to print a pattern with varyingly long elements, colour changes at a constant point at the start of each element of the pattern. That way the user can say that leg (say) 5 of the pattern had the colour change happen exactly at the corner. Each leg would correspond to a specific colour change purge length.
An array of these patterns could then be printed for each colour combination desired, and speed desired, and the script would take these user inputs to inform how far in advance to time the change.
I can draw a picture if that helps
