Poor surface finish
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I am struggling with a number of issues with print quality with a Jubilee printer. I am printing PLA at 200 mm/sec at 230C with a Dragon hot end and a BMG clone extruder.
The picture shows horizontal (rotate picture 90 degrees) lines of a print that is basically a box. The closeup shows holes in the print. Also attached to the edge of the holes are little bobs of filament that look like zitz in the print. They are pretty much random all over the place even though my Z seam is set for 'sharpest corner'. These holes show up in the middle (well anywhere really) of straight horizontal filament runs.
My initial guess was moist filament with gas bubbles forming and interrupting a layer line.
I attempted to dry the filament (9 hrs at 50C in a dehydrator) but I see no improvement.
I am also concerned that the hole in the middle of the picture spans three layer lines which I don't think makes sense with my wet filament hypothesis.I would appreciate some feedback about possible causes for what I am seeing.
Oh, I have tried two different tool heads with the same end result. Faster printing shows more of these 'dropouts' compared to slower prints but they are still there.
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I don't know anything about your printer, hotend, filament or model, but I print at 65mm/second and that seems fast to me.
Could it be that your extruder can't keep up at 200mm/second?
Try printing at 50mm/second and let us know how the surface finish is. If it's good, I think you have your answer.
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@alankilian, thanks for your input. The Dragon HF version , high flow) has been tested at 24 mm3/sec so it can definitely handle that. This print is 0.4 mm wide and 0.2 mm tall so at 200 mm/sec that is 16 mm3/sec. Lots of head room.
If I print slower I see fewer 'holes' but they are still there. I had to look under a microscope to see what exactly was going on - the surface has tiny little zits on it that you can feel. The actual holes are not really visible without a microscope. In the picture above, you can see how immediately before the hole, the filament stops getting laid down smoothly and it actually tends to form a bit of a bump.
Thinking a bit more about it, could this be a case of too much heat? As mentioned, I run at 230C. If I print at 100 mm/sec I would drop the temperature down to 210. The higher temperature is used to increase the flow capacity of the hot end. The thing that I don't understand here is that everything prints fine with a nice bead being laid down and then all of a sudden there is a big nothingness ... but the holes do look like they were almost melted into the layers (by the way the hole edges look like).<shrug>
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@jens55 Don’t trust in tests and what they say. For high quality at high speed, you must well balance your system.
The higher the throughput of filament, the more heat you must apply - that’s possible, but at the cost of precision. Start with something like 40-60 mm/sec. and narrow down on the proper temperature in steps of +/- 5 degrees - depending on the specific PLA filament, a range of 180 - 220 °C has to be tested.
Another thing to consider is filament quality: I have seen incredible variances in diameter and some really bad chemistry, resulting in the effects you describe - and worse: clogging the nozzle in regular intervals. Try different brands and/or another color. That can make a huge difference.
When you get good results at low speed, with the optimal temperature for a filament that works flawlessly, you can begin to speed things up.
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@arnold_r_clark , well it didn't make any difference to go to 210. The only reason I went to 230 is because of the high extrusion rate.
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@arnold_r_clark . go hotter ???
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@arnold_r_clark no, I am trying to figure out what you meant. I said 230, you said too hot, I said I tried 210 with no difference, you said 'if its not working one way go the other....'
I took that to mean if going colder isn't working, try hotter .... which sounded weird so I wanted to confirm what you were trying to say. -
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@arnold_r_clark fair enough....
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Are you running a print cooling fan? How large is the print? What is the acceleration setting? How big is the nozzle and what is the printing line width?
If you're trying to print a small object super fast you need to have a LOT of cooling capability. Otherwise the extruder keeps dumping hot plastic on top of hot plastic and that can cause all sorts of problems.
If you're trying to print a line width smaller than the nozzle diameter all bets are off. It is going to come out bad at any speed.
Try printing two or three of the prints at the same time to allow some time for the plastic to cool before the extruder comes around again for the next layer.
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@mrehorstdmd, no cooling fan, print is roughly 100*150 mm and 130 mm tall, I tried many different acceleration settings with the latest one being 5000 (IIRC), 0.4 mm nozzle, 0.4 line width, 0.2 mm line height, layer time is in the one minute area depending on speed of course. The entire print takes around 9 hrs more or less depending on speed.
I have an excess of printed models now so I have designed something much faster to print. I was also getting extremely frustrated with this issue. There are other issues but this one seemed the easiest to solve (famous last words). First attempt is a round hollow tube, 75 mm diameter, 75 mm tall, 1.2 mm wall thickness printed spiralized for the first attempt, 200 mm/sec with 5000 acceleration, 0.4 nozzle, 0.4 wide line, 0.2 mm line height, cooling at 30%, estimated print time 20 minutes. This is a sort of baseline print for me and I will tweak the speed to begin with - lower if I have the pockmarks, faster if it comes out as a clean print. Next will be to switch to normal, non spiralized mode.
My thought here is that printing a round object avoids sudden acceleration changes in spiralized mode and limited opportunity to screw up in the regular mode with three layer width for the wall. After that I will probably try a square model and various speeds/accel/jerk/etc settings.
I have to get this sorted somehow .... a friend prints with an almost bog straight CR10 and gets a perfect finish while my friggin' expensive Jubilee can't print even basic stuff correctly. Yes the CR10 prints a lot slower and I get a good finish if I print at CR10 speeds but the CR10 is a bed slinger with lots of mass while I am only moving a small light tool. I should in theory be able to print at 300 mm/sec with 600 mm/sec travel moves with a 0.2 mm thickness line, 400 mm/sec print speed if I go down to a 0.15 mm line height. These speeds should max out the capability of the hot end but be doable without weird artifacts in the print. -
So it turns out that I obviously have no clue of what I am doing ..... I printed my spiralized tube with specifying 200 mm/sec for speed in Cura. DWC shows a speed factor of 100% yet the 'requested speed' in DWC is only 81 mm/sec. For the life of me, I can not figure out why when the slicer is set for 200 mm/sec, the printer is only been asked to print at 81 mm/sec. Acceleration is at 5000 so IMHO, the acceleration shouldn't limit the print speed.
So yeah, testing isn't going to show anything until I figure out the very basics of printing
BTW, I did increase the speed factor and although print quality went to crap from under extrusion, I was able to run the printhead around at 200 mm/sec .... which seems to suggest that there isn't some hidden limit that I somehow manage to hit.
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Somewhat aside, this article is interesting: Investigating the effect of fabrication temperature on mechanical properties of fused deposition modeling parts using X-ray computed tomography. It is about experiments printing with PLA between 180C and 260C, and shows that PLA can benefit from being printed at temperatures as high as 260, leading to higher density, lower internal porosity and improved interlayer adhesion, making for stronger parts.
Of course you need a hotend that can do this and probably appropriate cooling setup (or print parts slow enough that they can cool down by themselves). But it certainly is not only possible but art times a good idea to print PLA at elevated temperatures.
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@oliof interesting ......
I am packing it in for now. The more I try to figure out why the speed that is being called for is 81 mm/sec when the slicer is set to 200 mm/sec, the more I am screwing things up.
The first print was perfect (other than slow), now about 3/4 of the tube is perfect and 1/4 has terrible layer alignment. That and some early moves that are not related to the layer issue now make really weird noises. -
Well crap ..... minimum layer time was set at 3 seconds and I guess that the layers tried to print faster than that ..... dropped it down to 1 second and it is running nicely at the set speed of 100 mm/sec.
Odd though that increasing the speed factor allowed the speed to go higher .... I guess because the minium layer time is enforced in the slicer and the speed factor setting is strictly on the printer.
It appeared though that adjusting the speed factor did not seem to change the extruder speed as increasing the speed resulted in under extrusion. Very odd .... -
Apparently as of RRF 31. speed factor does not affect extrusion speed. I am not sure why this was changed from the earlier versions of RRF where speed factor modified all speed settings including extruder speed.
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@jens55 a low jerk setting could be limiting speed on a circular print.
