@sethipus said in Blobbing/zitting that wipe/retract won't fix?:

I think what you're seeing there is related to the fact that retraction isn't instant. If it's retracting there, and if you're not doing retraction during a wipe, the nozzle will have to stop there momentarily to do the retraction, and that non-zero time spent with not-yet fully retracted filament is simply causing that extra little bit that blobs slightly at the start and end points, making that seam. If you're not retracting there, and it's going from one side of that seam into interior lines, then some combination of PA and acceleration and jerk in X or Y might reduce that, but you'll almost certainly never get rid of it completely.

What would be an interesting test, if you want to insert g-code in at various levels of the print to see the effect, would be to start with low jerk, acceleration, and max speed of your extruder, and up those values at certain intervals, and see if the seam changes in appearance. I'll bet it does. Up to a point, anyway; beyond a certain speed, depending on the extruder, you simply might be unable to retract it any faster without stripping and slipping.

Cube on left is without wipe, cube on right is with wipe. Doesn't appear to make a difference. I think the issue is that PA is appearing to do nothing. Even if marginal, my printer is not doing anything different at different PA values.

@dc42 said in Blobbing/zitting that wipe/retract won't fix?:

@shensmobile said in Blobbing/zitting that wipe/retract won't fix?:

The command I'm supposed to be issuing at the start of the file to trigger PA is M572 D0 S0.05 right? And inserting that command (with a new S value) at various points in my GCode should change PA from that point onwards, right? If so, I wonder if there could be another configuration setting that's preventing PA from being effective.

Yes, assuming the tool you print with uses extruder drive 0 (D0 in the corresponding M563 command).

What retraction speed do you use?

60mm/s. I wonder if it's because my extruder accel/jerk are too high. They're at 4000/4000, perhaps when PA is doing its thing, my extruder can't keep up with those values and slips? If that sounds reasonable, which do you think would be most effective to drop? Accel or Jerk?

I printed with higher quality filament and the seam/sitting is definitely still there. I did the calibration cube again with the following settings:

2mm retract
60mm/s retract speed
No wipe/coast
180c print temp
Aligned seam at the rear of the cube

Here's the seam along the back:

The rest of the print is fantastic (no voids, straight walls, great looking X and Y cutout) but this damn seam is still there. What's crazy is that I upped PA from S0.05 to S0.09 gradually throughout the print. The seam doesn't seem to be improving at all, and neither do the corners or the look of the top infill. I almost feel like maybe PA isn't taking?

The command I'm supposed to be issuing at the start of the file to trigger PA is M572 D0 S0.05 right? And inserting that command (with a new S value) at various points in my GCode should change PA from that point onwards, right? If so, I wonder if there could be another configuration setting that's preventing PA from being effective.

@dc42 100% agreed, I hate that I'm using coast. That's why I don't want to use it, although in PrusaSlicer's case, it's a tiny coast just to account for the thickness of the line that gets extruded, so I can see why they included it by default.

I have 1mm of retraction right now, and e3d recommends less than 1.5mm for retraction (I believe). Any more than 2mm and I get jams/clogging. I just went through that brutal experience before my vacation. It's a direct drive, so no bowden tube here. I should be able to get away with small retraction.

I'm going to try with no wipe and see if PA can do its job more effectively. That's the only variable I haven't eliminated.

Update:

Disabled wipe, upped retraction to 1.5mm. Ignoring the stringing and the gaps (this filament pops/fizzes a bunch, I think it has a ton of moisture in it, it's almost 6 years old), I think this is the best looking blobbing so far. Now what do I try from here?

@phaedrux Sorry it's taken so long for me to get back to you. I went on vacation shortly after your last message.

I've been tinkering all morning, even designed a new "calibration" print to figure out what's the optimal PA value to use, and... yeah still nothing. The biggest improvement is still going from Simplify3d to PrusaSlicer, and it's because PrusaSlicer has "coast" sort of built in. That is, on the outer perimeter, it stops before it completes the loop to account for the extrusion width at the start and end of the perimeter.

I simulated this in Simplify3d by adding 0.5mm coast and it helps a lot there too.

Here's the best print I've gotten so far today, using PrusaSlicer:

I know there's quite a bit of ringing, I have to turn down the jerk on XY and that'll fix that right up (I copied your settings you posted blindly, whoops). The zits/seams on the corners are much better, but they're still there.

And here's the .3mf for this print job: https://www.dropbox.com/s/aw8wqs696kqcvnt/xyzCalibration_cube.3mf?dl=0

I've gone through what it could possibly be, logically, and I'm stumped. I'm starting to wonder if my tension isn't high enough on my idler and PA isn't able to jerk the filament up fast enough, or if it's just this filament. I am using the most garbage PLA I have right now to run these tests, I wonder how much of an impact it has. I'm printing at a pretty low temp (180c) so retraction/PA should have more of an impact on blobs/zits, but it doesn't seem to change much if I print hotter. I'm going a little nutty-bananas now

PA at 0.15 with extruder jerk/accel/retraction speed increased to @Phaedrux settings: https://imgur.com/a/qopefEY

Honestly doesn't look any different than my other prints. Watching this print though, I think that my original hypothesis was either incorrect or has been fixed with the new settings. The start of the inner perimeter no longer has a large blub at the beginning; however, when it finishes the inner perimeter and moves to the outer perimeter, it almost feels like it's oozing a bit during the tiny, fraction of a mm travel and it creates a large "extrusion" between the two layers that the extruder runs into at the end of the outer perimeter.

I'm running a PrusaSlicer generated file now with my old retraction/PA settings, except I noticed that PrusaSlicer is doing the external perimeters slower than I'm telling it to. Watching it print slowly, I see that it's producing the tiniest little "extra extrusion" when it goes from inner perimeter to outer perimeter, probably because it doesn't have as much pressure built up in the nozzle.

@deckingman Just put new bearings in and the Titan Aero has the metal cover, so I don't think so to either of those. I think the clicking was because with a PA of 0.4 on such a small object, during infill, it would basically be retracting and unretracting constantly at every zig zag.

@nophead Ah that makes a lot of sense. Calculus was a clever way of explaining that concept. I'm gonna try increasing my jerk/accel again and increase the retract speeds

@Phaedrux thank you so much for your settings. I'm gonna try those next. Is everyone using firmware retraction? I presume that firmware retraction means that you aren't able to do retraction during wipes? Also, sorry for the dumb question, but what's the advantage of firmware retraction? In another post, dc42 seemed to confirm that firmware retraction is basically the same as issuing a G1 E# F# command, which is what slicing software already builds in. Does the duet do some other calculations with firmware retraction to improve print quality?

Will report back after trying all of these suggestions. I may stick to a PA of 0.05 for now and see if the increased jerk/accel for extruder, as well as increased retract speeds, will help.

@nophead I definitely need to look into firmware retract. It makes sense that the printer should adjust retract based on speed and flow rate. I am curious about why un-retracting is what prevents blobs. When you're un-retracting, aren't you adding material into the extruder, increasing pressure? In that case, I would think that unretracting too early/quickly is what causes blobs. I'm trying to wrap my head around the fundamental principals here at play.

And yes, my slicer is definitely doing the same amount of retract/unretract no matter what is actually being done. Pressure Advance is supposed to account for this, by adjusting flow rate based on extruder changes, but it actually increases pressure at the start of lines.

@deckingman I'll try higher PA for sure today then. I accidentally went to 0.4 (thinking it was 0.04) and the Titan just made clicking noises all print, so that's probably too much, but I'll definitely try some larger values than 0.1 and see if it improves these zits.

Thanks for your help everyone

@burtoogle

Yup! Turned off wipe, turned off retraction, tried MASSIVE wipes and MASSIVE retractions, it doesn't change much. Turning PA up had the most effect so far but it seems crazy to have a direct drive at S0.1 when the recommended is S0.05 or lower. Even then, these zits are still there.

Is it possible that this is just a limitation of FDM? I've seen from a couple of posts on Reddit and even here that Z-seams are just a fact of life with FDM and that turning a setting on might fix it now but will cause problems later (coast in this case?).

I think that phenomenon comes from the previous few lines of GCode. It's doing the retraction during the wipe movement. See here:

G1 X8.144 Y-9.063 E9.81967
G1 F14400
G1 X8.282 Y-8.690 E9.77246
G1 X8.346 Y-8.253 E9.72004
G1 X8.322 Y-7.816 E9.66810
G1 X8.274 Y-7.598 E9.64155
G1 X8.198 Y-7.379 E9.61408
G1 X8.088 Y-7.161 E9.58504
G1 X7.940 Y-6.943 E9.55371
G1 X7.754 Y-6.724 E9.51969
G1 X7.125 Y-6.069 E9.41183
G1 X6.958 Y-5.851 E9.37915
G1 X6.826 Y-5.632 E9.34890
G1 X6.729 Y-5.414 E9.32049
G1 X6.660 Y-5.195 E9.29331
G1 X6.596 Y-4.759 E9.24089
G1 X6.620 Y-4.322 E9.18894
G1 X6.668 Y-4.104 E9.16240
G1 X6.744 Y-3.885 E9.13493
G1 X6.854 Y-3.667 E9.10589
G1 X7.002 Y-3.448 E9.07456
G1 X7.188 Y-3.230 E9.04054
G1 X7.817 Y-2.575 E8.93268
G1 X7.984 Y-2.356 E8.90000
G1 X8.116 Y-2.138 E8.86974
G1 X8.116 Y-2.137 E8.86967
G1 E8.81967 F1800.00000

Extrusion goes from 9.81967 to 8.81967.

From the G-Code itself, I don't see anything that would cause the zit.

Edit: For the record, I think I'm going through the exact same thing as this fellow: https://forum.duet3d.com/topic/849/tweaking-for-perfect-jerk-accel-pressure-advance-blob-removal

0_1563485089097_xyzCalibration_cube_prusa.gcode

Line 567 is where it finishes the infill before it starts the perimeter that has the lowest zit in my picture. I think this is one of the files where I took it back to basics with 1mm retraction, no extra length on restart, and PrusaSlicer controls the wipe distance (it's exactly how long it takes to retract filament). I did have PA turned up to 0.1 though.

0_1563486219982_xyzCalibration_cube.gcode

This file does it as well. Slightly different settings, and from Simplify3d, but starting from line 645 is where it begins the perimeter that will lead to a zit at the same location as the other file.