Print quality - low jerk low acceleration
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You can also throw in filament temperature, filament type and of course nozzle diameter. The maximum acceleration can be calculated if you know the mass of the axis and the torque of the motor. But you'll likely end up setting it lower than this for better print quality. You can set maximum speed to anything you like as long as it's on the high side, as the actual move speed will be governed by the slicer settings or the feedrate that you set for non print moves such as homing and probing. The real maximum print speed will be determined by how fast you can melt filament and will almost always be lower than the capabilities of the printer mechanics and motors.
If you really have a masochistic streak, then you can try using a mixing hot end which opens up a whole new world of other factors. When you hold filament in the melt chamber for maybe hours at a time without it moving forward all sorts of wonderful things happen like PLA starting hydrolyse which results in over extrusion, and PET-G swelling in the heat break area which screws up retraction. Mixing hot ends should really come with health warning…..........
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Thank you I really think this level of discussion regarding speed, jerk and acceleration should be in the wiki. it certainly helps me understand the basic and enough of a guidance for me to know what to tweak next.
Stephen
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I think there is probably a presumption (correct me if I'm wrong) that those buying Duet controllers, as probably the best controller on the market and one of the most expensive, come to it with some 3D printing experience. Of course, that's not always going to be the case, but a link in the wiki to some other basic guide to 3D printing might be a good idea. There's plenty of them around.
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I can concur with that presumption… the people that hang around here seem to know a ton about this stuff.... which is awesome btw and I'm glad that I dove into Duet
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I'd say this is probably the most helpful, polite and free of BS 3D printing forum I've come across.
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I'd say this is probably the most helpful, polite and free of BS 3D printing forum I've come across.
+1.
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+1 Indeed.
I really enjoy reading this forum. -
+1, I regularly stalk this forum just to absorb some of the ludicrous amount of knowledge contained herein.
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here you go 950 vs 50 jerk setting left to right marvin respectively. Thanks
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That's better then. It also confirms my theory that most instances of "ringing" aren't actually caused by the print head vibrating due to some sort of resonance, but rather that the print head was doing exactly what it was told to do, and in this case it was due to the instantaneous speed change ("jerk" as we have to call it) being set too low. Glad it worked for you.
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Very interesting! So, a simple cylinder can highlight this?
I guess that the instantaneous speed change should be as low as possible, to avoid shaking to much the machine, but high enough to avoid such artifacts. Am I right ? So, one should start with a low value, print some cylinders with different diameters (smaller ones should have more artifacts, right?), and increase the value until artifacts are gone?
And if they don't go away, this means than there is a mechanical issue…
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Yes that pretty well sums it up - works for me anyway. I create the cylinders using OpenScad and set the number of segments to 100 ($fn) so the size of each segment will increase as the diameter of the circle increases.
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Yes that pretty well sums it up - works for me anyway. I create the cylinders using OpenScad and set the number of segments to 100 ($fn) so the size of each segment will increase as the diameter of the circle increases.
One effect of using a constant $fn is that the angle between segments will always be the same. It's the angle between segments that determines the minimum value that the XY jerk needs to be for a give print speed. The theoretical minimum XY jerk you need is approximately (printing_speed * 6/$fn) when $fn is large.
To check that you haven't set the jerk too high, print octagons and see how the machine sounds.
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That sounded very subjective… I'll see if I can find octagons to print. How does it should sounds like if jerk set too high? Rough corner turn? Banging sound perhaps?
Stephen
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Banging sound.
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It is subjective to some extent but you can still compare one setting against another. It;s how it prints that's important but in my experience if it sounds "rough" or the motion looks "rough", it prints "rough".
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One effect of using a constant $fn is that the angle between segments will always be the same. It's the angle between segments that determines the minimum value that the XY jerk needs to be for a give print speed. The theoretical minimum XY jerk you need is approximately (printing_speed * 6/$fn) when $fn is large.
To check that you haven't set the jerk too high, print octagons and see how the machine sounds.
Fair comment. My rationale about using the same $fn was to keep the angle the same but vary the length of the segments, but what you say is also a valid approach - possible more so.
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If you have over extrusion in corners, try increasing pressure advance.
I made a test on a simple 20x20x2 cube: I used 0.1, 0.2 and 0.4, but it didn't improved (not even really changed) the over-extrusion in angles. In fact, the angle where extrusion stats/stops at each layer is worse.
I also tried to increase jerk on E, from 10mm.s⁻² to 20mm.s⁻², without success.
Any idea why? Could it be another problem?
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@fma:
If you have over extrusion in corners, try increasing pressure advance.
I made a test on a simple 20x20x2 cube: I used 0.1, 0.2 and 0.4, but it didn't improved (not even really changed) the over-extrusion in angles. In fact, the angle where extrusion stats/stops at each layer is worse.
I also tried to increase jerk on E, from 10mm.s⁻² to 20mm.s⁻², without success.
Any idea why? Could it be another problem?
Can you post the photos?
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Cf
From left to right :
0
0.2
0.4
0.4 with jerk doubled (10 -> 20mm.s⁻²)The in/out angle is the top right.
