Why am I having to run with an extrusion multiplier of 60%?
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OK folks. Here is the latest. I changed the steps per mm from 424 to 405 as indicated by the ratio of filament used compared to filament expected. Re-printed the 1cm^3 cube and measured the filament used. This time I got 410 actual vs 417 expected - not too bad and it shows that changing the steps per mm has the expected effect. However, the finish on the cube itself was pretty dire. One corner showed distinct bulging and the surface finish on the top was very "ribbed", although the sides look good. Then I printed another cube with an extrusion factor of 80%. So I was expecting to see 410mm (the previous value) x 0.8 = 328 mm. The result was…...........330mm. Spot on. So that proves to me that everything is working "extruder wise" as it should.
What is freaking me out though, is that the finish on this last cube is PERFECT. It's silky smooth all round, including the top. No lumps or bumps, no bulging corners. When I measure it, it is a little small. Height wise it is 9.87 mm and width wise (both X and Y are the same) it's 9.71. So around 1.3% in height and 2.9% in X and Y.
How can this be with genuinely 20% less plastic extruded?
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I seriously think that assuming its a corexy issue is a red herring - I'd be interested if you prove me wrong but corexy is just a kinematic scheme I can't see how it requires any different extrusion settings. The two titans I have to "under extrude" with if you follow that logic are both installed on deltas.
I will when my current print finishes closely inspect and measure the drive gears on each titan.
Yes, it could well be Red Herring - I admit I'm clutching at straws.
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Hi Ian.
I think you have proved the issue lies at the slicer end because you did a print and there was only ~4% variation in the gcode commanded extrusion and what actually happened. Modifying your steps/mm so that error is reduced to a minimum will confirm this.
I recommend trying another slicer like Cura (I use an older version as AFAIK the newer versions don't support as many printer types).
Hi Tony,
I don't see how it's the slicer. The numbers it came up were perfect for a 1cm^3 cube. I've modified the steps per mm and re-printed the cube and it used the correct (theoretical) amount of filament. So slic3r does all it's little calculations then at the end, adds them up (at least I'm assuming that's how it works) and comes up with the exact amount of filament and print volume.
….........But I'll try Cura at some point.
Ian
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Hi Ian
I have never tried to check a slicer's volumetric output , vs what you should expect.
My point is simply that if the entire printer system (ie the mechanics, firmware, electronics) is doing precisely what it was commanded to do by gcode (ie extrude exactly N amount of filament) then the issue must logically be what it it being told to do by the slicer is not correct. I know that is not particularly helpful in saying what is wrong, which is why I suggested another slicer.
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Hi Tony,
I hear you and a different slicer has to be worth a try - if only eliminate the possibility that Slic3r is at fault.
What I'm trying to get my head around is that I have proven that the entire print system is doing what it's supposed to do and extruding exactly the right amount of filament, as dictated by both manually extruding a fixed amount and by dynamically extruding an amount dictated by the gcode generated from a slicer. Also, it's not specific to any particular object. It's the same for a tiny 10mm cube and a giant 320mm tall x 220mm diameter "crinkly shaped" vase. Yet there is something wrong with my machine which means that, in order to get a good quality print, I have to extrude at least 20% less filament than is optimal.
My current line of thought is that 1mm^3 of extruded filament wants to take up more space than 1mm^3. Or alternatively, 20% less extruded filament is required to fill a given volume. Hence the poor surface finish bulging at the corners, and the tendency for the print head to drag on the recently extruded filament when using an extrusion factor of 1.00.
So why could this be? I'm aware that filament expands as it comes out of the nozzle - die expansion or some such I believe it's called. But it should shrink again as it cools. If it didn't shrink as expected for some reason, then that would account for it, but of course that begs the question "why doesn't it shrink back after expanding". Alternatively, if there were gaps between the lines of filament, then a smaller extruded amount would be needed to fill a given volume. That would also account for it, but there are no visible gaps that I can detect with the naked eye - certainly not 20% worth of gaps.
What if the nozzle diameter is (say) 0.6mm ( I won't know until I measure it) and I've told slic3r it's 0.5. In theory, it shouldn't affect the volume extruded but I'd expect the slicer to adjust the width between each line accordingly. If it comes out of the nozzle 0.6mm wide but slic3r spaces the lines 0.5mm apart, would it have the effect of squashing the lines together, making them bulge upwards? If it did, it would like a severe case of over extrusion as subsequent layers would compound the problem.
There's a thought….........
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The only times I've ever had over extrusion caused by the slicer, was when I accidentally used settings for 1.75mm filament for a 3mm filament printer and when I had the wrong nozzle size, set it for .5mm and it really was .4mm.
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My understanding is that die-swell occurs most in free air and is approximately 20% for the materials/temperatures we use routinely in 3d printing. However it does not occur in the same way when you lay filament down onto a build plate or a previous layer, then it is less as the filament is constrained as it is extruded. ABS shrinks by around 0.7% on cooling but this is an order of magnitude less than the "effect" you're measuring.
Try printing some cubes with different nozzle sizes selected in slic3r. I can print with a 0.4 nozzle using slic3r set for a 0.3 nozzle and it works, sometimes the prints even look a little sharper, but the top solid infill isn't always as good, though often slic3r doesn't do such a good job of top solid infill anyway. I think all that happens is the default extrusion width reduces, and the minimum feature size reduces too, but with the larger nozzle tiny features are likely to be fuzzy.
To take your example in the last paragraph, I'm not sure that would happen. Firstly the spacing between the lines isn't usually your nozzle diameter because of the die swell. So Slic3r prints 0.48mm extrusion width (spacing between the lines) for a 0.4mm nozzle as a default, you can change it under the advanced tab. If you're laying down filament with a 0.6mm nozzle but slicer is setup for a 0.5mm nozzle, then the lines are by default 0.6mm apart, however they aren't going to bulge out (might do on first layers but that isnt unusual is it) as it is extruding the volume correct for a 0.5mm nozzle. This is the same as me printing with a 0.4 but using settings for 0.3mm - it works although some details are going to be poor. I suspect for a simple cube you wouldn't even notice the difference. It might explain your issue, but it doesn't explain why I see the same effect as I am using a verified 0.4mm nozzle and settings for 0.4mm and getting great prints but sending around 75% of the steps/mm to the extruder than I (supposedly) should.
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@DJ. I'm not using default values. Slic3r is set in my advance settings to 0.5mm thick so this will override the default width. So if my nozzle is actually 0.6 dia, but slic3r is extruding setting the lines to be 0.5mm apart (as set in the advanced tab) then surely that will have an adverse effect.
I'm not saying that is the cause but just maybe….....
I appreciate everyone's help but it just seems to me that whatever theory I come up with to try and explain what's happening, it just gets dismissed as not being feasible. I could do with some positive suggestions or ideas.
Sorry, it's been a long day. I've been playing around with this since 8.00 am. It's now 10:15 pm and I'm no further forward.
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Have you tried a different roll of filament? Maybe that one expands more than usual.
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Have you tried a different roll of filament? Maybe that one expands more than usual.
Yes, - about 5 rolls and in all 3 extruders too.
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The tracks don't lay down like bricks - in practice, there's a tiny bit of air that gets trapped. It takes less than 1 cm^3 of filament to make a 1cm^3 "solid" cube.
Any chance your filament diameter exceeds what you've set in the slicer?
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I am having similar issues with my corexy machine as well with titan. using the e3d recommended steps per mm i have to reduce the extrusion multiplier to 84% for 200micron layer height to not over extrude like crazy. When I was using just a regular bowden extruder the steps per mm was spot on and i had no issue with leaving extrusion multiplier at 100%. This is all with simplify3d as slicer.
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The tracks don't lay down like bricks - in practice, there's a tiny bit of air that gets trapped. It takes less than 1 cm^3 of filament to make a 1cm^3 "solid" cube.
Any chance your filament diameter exceeds what you've set in the slicer?
Understood and I can accept a few percent but 20% worth or air? I think that would be visually noticeable. Filament diameter is spot on, if anything slightly under. All rolls tested come out at 1.74 to 1.75 depending on where they were measured and slicr3r is set to 1.75. Thanks for the thought though.
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I am having similar issues with my corexy machine as well with titan. using the e3d recommended steps per mm i have to reduce the extrusion multiplier to 84% for 200micron layer height to not over extrude like crazy. When I was using just a regular bowden extruder the steps per mm was spot on and i had no issue with leaving extrusion multiplier at 100%. This is all with simplify3d as slicer.
Interesting. However, from all the testing I've done so far, I'm now convinced that the Titan is doing what it should. i.e. you ask it to deliver x amount of filament and that's exactly what it does. In a way, I'm pleased that I'm not the only one but it's frustrating to not know the cause.
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Quick update. I set the nozzle width to 0.6 in slc3r and tried a test print with extrusion factor set to 1.00. Severe signs of under extrusion - gaps between the lines, poor layer adhesion. Bang goes another theory but there something very weird going on which I'll photograph later when the bed cools down.
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This is the weird thing I was talking about. Sorry, I don't know how to get pictures in posts but here is a shareable link to my google drive folder.
https://drive.google.com/drive/folders/0B_MwtHtQR_ZvZDMxb3FIWnE5RGs?usp=sharing
It's 2 cubes created in OpenScad as a single object. They are 80mm square. This single file was then rendered and saved as an stl. It was then opened in slic3r, the layer width was changed from the 0.5 that I had been using to 0.6 then the gcode files exported. Then it was printed but the print aborted after the first layer. It is under extruded and that is due to the change in layer width. But why the weird pattern on the left hand cube compared to the right? The infill direction was 45 degrees. This means that for BOTH cubes, only one of the XY motors was running to give the same 45 degree movement, from near left of the build plate to far right.
The build plat is flat and level - trust me. It's a 10mm thick machined aluminium tooling plate on top of which is 6mm flat glass. Probing the bed at the 3 points where the screws are, shows all 3 point to be within 0.05 mm and that's on a 400mm square. The object was centred on the bed.
All explanations and theories gratefully received.
Ian
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Hi Ian,
Apologies if I have been negative that's not my intention, its just the extrusion issue whilst annoying is not going to, and hasn't stopped you from printing well it just means changing a setting that makes no sense i.e. set steps/mm to 300 instead of 400. But then if it works why be so concerned about it?
As for the images there is clearly a big difference between one motor turning (the 45 deg rotated object), compared to when two motors are turning. They are both underextruded, as that is a first layer you would expect filament to pile up due to first layer squash-down (unless you are deliberately setting your nozzle to bed gap higher, "laying" down the filament rather than squashing it down). Because you're underextruding the filament is being pulled thinner than it should be. In the non-rotated object Its almost like the extruder is pulsing, like a direct drive mk8 or similar with low steps/mm but with titan being 3:1 geared pulsing isnt normally noticeable. Also I cannot explain why the pattern appears when two motors are turning rather than just one.
Simon.
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This is the weird thing I was talking about. Sorry, I don't know how to get pictures in posts but here is a shareable link to my google drive folder.
https://drive.google.com/drive/folders/0B_MwtHtQR_ZvZDMxb3FIWnE5RGs?usp=sharing
It's 2 cubes created in OpenScad as a single object. They are 80mm square. This single file was then rendered and saved as an stl. It was then opened in slic3r, the layer width was changed from the 0.5 that I had been using to 0.6 then the gcode files exported. Then it was printed but the print aborted after the first layer. It is under extruded and that is due to the change in layer width. But why the weird pattern on the left hand cube compared to the right? The infill direction was 45 degrees. This means that for BOTH cubes, only one of the XY motors was running to give the same 45 degree movement, from near left of the build plate to far right.
The build plat is flat and level - trust me. It's a 10mm thick machined aluminium tooling plate on top of which is 6mm flat glass. Probing the bed at the 3 points where the screws are, shows all 3 point to be within 0.05 mm and that's on a 400mm square. The object was centred on the bed.
All explanations and theories gratefully received.
Ian
That's a very interesting pattern. Send me the gcode file and I'll try it on my Ormerod in CoreXY simulation mode.
What happens if you change the infill direction to 0 degrees?
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Hi Ian,
Apologies if I have been negative that's not my intention, its just the extrusion issue whilst annoying is not going to, and hasn't stopped you from printing well it just means changing a setting that makes no sense i.e. set steps/mm to 300 instead of 400. But then if it works why be so concerned about it?
As for the images there is clearly a big difference between one motor turning (the 45 deg rotated object), compared to when two motors are turning. They are both underextruded, as that is a first layer you would expect filament to pile up due to first layer squash-down (unless you are deliberately setting your nozzle to bed gap higher, "laying" down the filament rather than squashing it down). Because you're underextruding the filament is being pulled thinner than it should be. In the non-rotated object Its almost like the extruder is pulsing, like a direct drive mk8 or similar with low steps/mm but with titan being 3:1 geared pulsing isnt normally noticeable. Also I cannot explain why the pattern appears when two motors are turning rather than just one.
Simon.
Hi Simon.
No probs. It's just that I don't like mysteries. There has to be a logical explanation and it's bugging me that I can't find it.
The under extrusion is due to me changing the setting in slic3r from 0.5 to 0.6. When I run 0.5, I get over extrusion (or some effect that looks exactly like over extrusion). It's looking like the sweet spot will be somewhere between the 0.5 and 0.6 but I need to do more tests to be sure. In any case, it seems that, for whatever reason, my machine is very sensitive to how the nozzle width is set in slic3r.
As for the patterns, the only time 2 motors turn is when it lays down the perimeter. For infill, it was near left to far right of the build plate for BOTH of the "cubes". That is to say, the left hand motor tuned but the right hand motor was stationary when doing infill in BOTH cases. It seems that when you set infill direction in slic3r it is the direction on the build plate, regardless of how the object perimeters are orientated. Don't forget that as far as slic3r is concerned, this was single object created from a single stl file.
So the mechanics/dynamics of the machine were identical (apart from the fact that one cube is physically offset to the right of the other). That's really freaking me out.
Ian
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That's a very interesting pattern. Send me the gcode file and I'll try it on my Ormerod in CoreXY simulation mode.
What happens if you change the infill direction to 0 degrees?
Hi David,
Thanks for the offer. How do I get the gcode file to you? Can't see how to attach a file by contacting you via this forum or by your web site contact form.
Cheers
Ian
