Vertical banding
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Hi
I'm no expert in this type of printer but do mechanical designs 2000h a year and will try to help.Since the pattern is so uniform the extruder can be excluded. It's not over under extrusion.
You have rails all around the machine so you know that the linear motion is without the pattern. You also know that the patterns are exactly straight in the Z direction –> the fault is in your XY plane. The carriage needs to wobble in the Y direction along the X linear rail. The pattern is very tight and I find it a bit strange because my guess would been that there is a pulley or two that are not concentric. But to get such a tight pattern means that the pulley is small or it has several high spots. I don't know exactly how an eccentric pulley would effect the print but I'm guessing exactly like your fault. The harder you tighten the wires the more motion is created by the elongation of the path.
It is very unlikely that it has to do with the card. It runs smooth as silk and even if it didn't the error is no were near enough to create such a pattern. It would require microsteps out of sync pulsating back and forth.
How have you made all the pulleys?
//P
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Hmmm…
It looks like the I get about 14 bands per 10mm.print a rectangular object aligned with bed so can identify axes, print at two different speeds. If same as my problem at 2x speed (faster) above will get 7 bands per 10mm.
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Hmmm…
It looks like the I get about 14 bands per 10mm.print a rectangular object aligned with bed so can identify axes, print at two different speeds. If same as my problem at 2x speed (faster) above will get 7 bands per 10mm.
I'm getting the same spacing at any speed, speed only seems to effect how visible the bands are, I suspect due to the mass of the extruder/gantry dampening out the vibration. The only change i can get in the spacing is by printing the test object at a 45 degree angle then its a constant 10 per 10mm with i suspect a linear transition to that point as the angle of the wall is changed from 0 to 45.
Hi
I'm no expert in this type of printer but do mechanical designs 2000h a year and will try to help.Since the pattern is so uniform the extruder can be excluded. It's not over under extrusion.
You have rails all around the machine so you know that the linear motion is without the pattern. You also know that the patterns are exactly straight in the Z direction –> the fault is in your XY plane. The carriage needs to wobble in the Y direction along the X linear rail. The pattern is very tight and I find it a bit strange because my guess would been that there is a pulley or two that are not concentric. But to get such a tight pattern means that the pulley is small or it has several high spots. I don't know exactly how an eccentric pulley would effect the print but I'm guessing exactly like your fault. The harder you tighten the wires the more motion is created by the elongation of the path.
It is very unlikely that it has to do with the card. It runs smooth as silk and even if it didn't the error is no were near enough to create such a pattern. It would require microsteps out of sync pulsating back and forth.
How have you made all the pulleys?
//P
Definitely, I agree its in the XY movement, not sure if its clear but this pattern is seen in both the wall in the X and the Y direction, so all sides of my little hollow test box have this pattern.
All XY 8 steel idler bearings (u groove) are of good quality and 11.33mm diameter where the line rides. The spectra line spool on the motors is 3d printed and 22mm diameter, while its not flawlessly round its not bad and any error caused i think seen over 10s of mm and not 14 in 10 mm segment.
While I love the Duet I am using the less common coreXY motion system and this issue can be hidden with slightly faster print speeds so I feels that its still on the table as a factor.
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I'm getting the same spacing at any speed, speed only seems to effect how visible the bands are, I suspect due to the mass of the extruder/gantry dampening out the vibration. The only change i can get in the spacing is by printing the test object at a 45 degree angle then its a constant 10 per 10mm with i suspect a linear transition to that point as the angle of the wall is changed from 0 to 45.
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All XY 8 steel idler bearings (u groove) are of good quality and 11.33mm diameter where the line rides. The spectra line spool on the motors is 3d printed and 22mm diameter, while its not flawlessly round its not bad and any error caused i think seen over 10s of mm and not 14 in 10 mm segment.Interesting, thank you for that. So next question is what do you have that is doing 14 repeats in however long 10mm segment takes? If the pattern is constant with linear travel of filament or carriage then it should all be geared together? Otherwise like on my issue you can calculate a per second frequency from the gcode.
Tooth marks from your extruder hob? As you note, pulley wheels and the like do not seem to cycle as quickly as this pattern.
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To see if it is an extruder issue, you can change the wall width, so the extruder will turn faster/slower per mm of wall, and so banding step should change.
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By running the machine faster you introduce more randomness to what the cords are doing and the speed makes jerks less impacting. I am still 90% convinced that there is some sort of concentrically issue. It is not easy to get artifacts as repeating as you have managed in other ways. The ball bearings should be good. And If mounted correctly, by fixating the centerpiece down to the base of the mount, there can't be any movement to them. If the bearings can't be bolted down add a shim above, middle and under.
Do you have the same bands on you pulleys? That can explain the problem. I think that if you spend the money on nice rails you should try to get the pulleys turned in a lathe or minimum put a metal sleeve above your printed part.
Can it be the patterns on the cords from how it is woven? I would say you have to many contact points with the cord to make it the most likely scenario.
You might also want to have some air in between the cords on the pulley. If the new cord clings to it's neighbor the effective diameter increases. but it would most likely not give this repeatability to your pattern.
The satisfaction once you solve this will be good
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@fma:
To see if it is an extruder issue, you can change the wall width, so the extruder will turn faster/slower per mm of wall, and so banding step should change.
But I doubt it is an extruder issue: bands would not be vertical, and angle should change depending on the perimeter length.
A friend had such issue; see entry #24:
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You have an unusually low steps/mm. My Scara printer also had low steps/mm and I could see on it that the arms were not moving smoothly even when doing raw motor moves that don't involve segmentation.
The cause was that not all microsteps are equal. Manufacturers of Nema 17 stepper motors make a greater or lesser extent to make them more equal, but this comes at the cost of reduced holding torque.
So if the spacing of the banding matches the full step interval, that's probably the cause. Solutions include:
1. Don't set the motor current too low. At low currents the detent torque causes the microsteps to be less even. Try 80% of the motor rated current.
2. Use 0.9deg motors. That's what I did.
3. Use smaller spools or possibly gearing to increase the steps/mm.
HTH David
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@fma:
To see if it is an extruder issue, you can change the wall width, so the extruder will turn faster/slower per mm of wall, and so banding step should change.
While I think the extruder is all but ruled out at this point as I cant see how any extruder defect would re align up perfectly each pass, this is a good suggestion for a easy test that I will try when i get home from work to make 100% sure.
By running the machine faster you introduce more randomness to what the cords are doing and the speed makes jerks less impacting. I am still 90% convinced that there is some sort of concentrically issue. It is not easy to get artifacts as repeating as you have managed in other ways. The ball bearings should be good. And If mounted correctly, by fixating the centerpiece down to the base of the mount, there can't be any movement to them. If the bearings can't be bolted down add a shim above, middle and under.
The metal idler bearings have a close tolerance to the 3D printer mount with 3 washers to prevent any friction. The clamping force is only light so the bearings could move slightly but as the angle of the spectra line on the bearings never changes i'm not sure how this would cause a issue as the bearing would be pulled to once side of the bolt and stay at that location. Feel free to correct me on that point.
Do you have the same bands on you pulleys? That can explain the problem. I think that if you spend the money on nice rails you should try to get the pulleys turned in a lathe or minimum put a metal sleeve above your printed part.
The pulleys don't have this banding nope. I totally might get the pulleys turned on a lathe if i can get the other mechanics sorted.
Can it be the patterns on the cords from how it is woven? I would say you have to many contact points with the cord to make it the most likely scenario.
Hmm i did not think of that one, here i was thinking i did not have to worry about any belt pitch or to turning over belts to run the belt flat side on the idlers. I will look in to this, this would be the worse case issue as it could scrap the entire design.
You might also want to have some air in between the cords on the pulley. If the new cord clings to it's neighbor the effective diameter increases. but it would most likely not give this repeatability to your pattern.
The satisfaction once you solve this will be good
I could space them a little father in the area im printing to check this perhaps. Yea, i really want to get this sorted, it could be ignored by finding the sweat spot on the print speed and such.
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You have an unusually low steps/mm.
HTH DavidYes, the spools are very big. But are motors that bad? It would have to be approx. a full 16th microstep out of sync. @David did it solve your issue?
Yes motors can be that bad, some are better than others. Even full steps can vary in size by up to 5%. Changing to 0.9deg motors helped me a lot, but didn't completely solve it.
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You have an unusually low steps/mm. My Scara printer also had low steps/mm and I could see on it that the arms were not moving smoothly even when doing raw motor moves that don't involve segmentation.
The cause was that not all microsteps are equal. Manufacturers of Nema 17 stepper motors make a greater or lesser extent to make them more equal, but this comes at the cost of reduced holding torque.
So if the spacing of the banding matches the full step interval, that's probably the cause. Solutions include:
1. Don't set the motor current too low. At low currents the detent torque causes the microsteps to be less even. Try 80% of the motor rated current.
2. Use 0.9deg motors. That's what I did.
3. Use smaller spools or possibly gearing to increase the steps/mm.
HTH David
I agree the steps are a bit low, while i can reduce the pulley size slightly I'm limited because it needs to spool the line from the diagonal bed distance ie bigger the bed the more line needs to be able to be spooled up. Also the smaller the pulley the more distance is covered by the line in the Z direction changing the line tension slightly.
1. For most of my testing the current is a bit low at 550mA, my motors are rated to 1.1 A. I did a test with 1.2A motor current with no reduction on the banding.
2. I did give 0.9 motors a go (see photos above) the band spaceing stayed the same and did not seem to reduce the issue any.
3. The spool size is limited by the bed size but with some changes and closer tolerances i might be able to reduce it a little but.
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You might like to try sticking a paper indicator on top of the spools, and see if the movement appears smooth or not.
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Yes motors can be that bad, some are better than others. Even full steps can vary in size by up to 5%. Changing to 0.9deg motors helped me a lot, but didn't completely solve it.
Good to know
I also have issues with how all drive pulleys are attached to the motors. This is a common fault on almost all machines. The front bearings of the motors are not designed to take up torque and that is how they are mounted now. To be 100% correct you should have bearings above and under the pulley and a somewhat flexible shaft to the motor. That can be simplified on almost all machines to the front bearing of the motor and a bearing above the pulley. Technical that constitutes an overrefined system but should be ok. On your machine I would go for a separate bearing above and under since the pulley is to high. Benefit is higher belt tension with less resistance.
An issue that might create ripples would be if your pulley is not fitting 100% to the shaft and rocks in the direction of the load. My guess is that it would be less repeating but it could still be the fault.
//P
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You might like to try sticking a paper indicator on top of the spools, and see if the movement appears smooth or not.
I will give that a try, also that gives me a idea, i could try removing the motor pulley entirely from the motor and see if i can still feel the vibration, that would rule everything out if it still can be felt. Unfortunately i don't think it would not confirm anything if it feels smooth because it may need that mass to produce the vibrations.
I also have issues with how all drive pulleys are attached to the motors. This is a common fault on almost all machines. The front bearings of the motors are not designed to take up torque and that is how they are mounted now. To be 100% correct you should have bearings above and under the pulley and a somewhat flexible shaft to the motor. That can be simplified on almost all machines to the front bearing of the motor and a bearing above the pulley. Technical that constitutes an overrefined system but should be ok. On your machine I would go fore a separate bearing above and under since the pulley is to high. Benefit is higher belt tension with less resistance.
An issue that might create ripples would be if your pulley is not fitting 100% to the shaft and rocks in the direction of the load. My guess is that it would be less repeating but it could still be the fault.
//P
I think we are well within any lateral load limits of the stepper bearings, don't forget the steppers have two bearings, one in the front and one in the back with a solid shaft so all loads are in the best direction for the bearing. Just don't get me started on Z axis lead screw loads, never liked that method
The pulley is vary snug, i have to use a screwdriver to pry them off after loosening all 4 bolts. Would be a cool trick to have the pulley vibrate over 100 times for a half rotation of the stepper hehe, not so sure that's the issue.
If i can create a little slip with the string on the pulley or the pulley to the stepper motor shaft that should unlink the stepper clogging from the banding position and perhaps i can get the banding to shift, that should rule out the mechanics and point directly to the motor or control.
Thanks for the input thus far guys, its nice to have feedback and someone to bounce ideas off of. I will do more testing when i get home.
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Tested the extruder to rule it out 100%. Here are 3 objects, lower one is 0.1, center one is 0.2 and top is 0.4mm layer heights. As you can see the the banding still line up, if the issue was anything do do the the extruder the spacing should go up or down as the plastic flow will double or half from the 0.2 baseline.
While it does look a little different the pattern remains constant spaceing.
Now for the smoking gun I think.
Here I loosened the bolt clamping the spectra line to the pulley and started a print, half way in i paused the print and commanded large X and Y moves. This lets the pulley wind and unwind nearly to the ends to encourage the line to slip slightly on the pulley. I then resumed the print, as you can see i got a slight shift mostly in the Y+ direction and for the first time managed to get the vertical banding to shift!The TLDR of that is i shifted the fullstep position of the motor to another location slightly in the print. In this case the slightly to the right in the photo.
So I feel that rules out most possible mechanical issues, that leaves me with my steps per mm are too low for the stepper drivers/duet or a strange fluke of the drivers/duet. Somehow it seems that the stepper motor is pausing/going slower at a full step location.
At this point i feel all i can do if give the 0.9 steppers another try and reduce my pulley size to the minimum diameter allowed by my bed size. If anyone has another take on things let me know.
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While I don't have any idea as to what's causing this, you can probably speed up your troubleshooting time by simply taping a sharpie marker to your hotend, and doing a test print drawing on a piece of paper instead of actually extruding anything: That should show the wobble I presume. If this was z-banding you'd need to actually print a tower. But since this is an XY wobble, you may give the sharpie method a go: I see people taping them to their CNC's to draw stuff… seems like it may apply here.
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Hehe, well I think i found my problem…. I was testing one thing at a time. It took the combined effort of boosted stepper current, 0.9 steppers and smaller pulleys. I went from a 22mm diameter pulley to 14mm the line barely all fits on the spool, this is the result.
I challenge you to find the vertical lines:)
Heated bed should be here this week some time, it will be nice to get rid of the blue tape, tiny bed and warped print corners. If i had to pick one I would stay the steps per mm was the main issue (as dc42 noted), it seems things act funny at such a low step per mm. For a reference I was using 45 step/mm for most of my testing, 90 step/mm with the 0.9 steppers (still banding) and 140 with both the 0.9 steppers and 14mm pulley.Thanks everyone for the suggestions and ideas, I hope this thread will be useful to someone in the future:)
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I'm glad you got it working.
It occurred to me that if the drivers have a problem with low current microstepping, this could also cause that banding. We don't normally see a problem with low current microstepping on the TMC2660 drivers in the Duet, whereas such problems are well-known with DRV8825 drivers. But if you were using a combination of low-inductance motors AND a low motor current, there could be a problem. In that case it would be necessary to adjust the chopper control register settings.
What is the specification of your motors, and what current do you have them set to in M906?
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This is what i changed to https://www.sparkfun.com/products/10846
0.9 degree
3.06V
1.7A (operating at around 1.2A i think)
1.8 OHM
2.8 mHThis is what i had before:
KH4234-b95101
1.8 degree
3.41v
1.1A (operating at 0.55 A)
3.1 OHM
4.4 mHAfter work I will drop the current down a little bit and see if the banding comes back at all. Is the "chopper control register settings" something i can change without recompiling the F/W? If so I would be happy to test any settings you like.
