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Posted · Bondtech extrusion issue?

I am struggling with one of my printer the last days. It keeps printing in bad quality with periodic underextrusion.

After switching nozzles, taking the print head apart and cleaning it and switching between different filaments I can rule out head / hotend and filament.

 

So I turned to the extruder today, it’s a Bondtech QR (https://www.bondtech.se/en/product/qr/) I am quite happy with for two years.

I disassembled it and cleaned it, though there was not much dirt. Also I could not see any mechanical defect or wear.

Remounted it and still there is this periodic underextrusion.

 

Observing the print I can a clear correlation with one rotation of the Bondtech gripper wheel and when then underextrusion happens:

You can see the set screw of the wheel pass by and the underextrusion happens in the same cycle. So the underextrusion cycle is identical with one full turn of the extruder gripper wheel which equals one turn of the stepper motor.

 

Attached a picture while the printer is working on the second layer, you see the stripes of the thicker and thinner extrusion.

 

So if it’s not nozzle, hotend, tube, extruder gripper wheel, what else could be the reason? Could the stepper motor have a defect in one area and loose steps just in like one fourth of it’s full turn?

Or is the gripper wheel worn but I just can’t see it? How long is a gripper wheel lasting typically? I think in these two years it could have been 1.000-1.500 hours of using it. No abrasive materials, 85% PLA.

 

I have both my printers modded as Mark 2 dual, so as a next step I could borrow parts of the 2nd extruder to check out if it’s motor or gripper wheel.

7DEAC11C-2ABA-4D14-AE23-B4E07812EEC7.jpeg

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Posted · Bondtech extrusion issue?
25 minutes ago, conny_g said:

Observing the print I can a clear correlation with one rotation of the Bondtech gripper wheel and when then underextrusion happens:

You can see the set screw of the wheel pass by and the underextrusion happens in the same cycle. So the underextrusion cycle is identical with one full turn of the extruder gripper wheel which equals one turn of the stepper motor.

 

According to the data sheet the QR is a geared feeder with a gearing ratio of 5.18:1

So the drive wheels and the stepper motor are not turning at the same ratio.

If  gripper wheel == drive wheel, you can probably rule out the motor.

 

Have you seen this thread, it looks pretty similar. Trying a different slicer can at least rule out a software issue (and is cheap...)

 

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Posted (edited) · Bondtech extrusion issue?

Um. Thinking out loudly. I am currently printing the same file with the same setting and the same filament on two printers of the same hardware, so I am quite sure that it’s not a software issue. Or I would see it on the other printer, too.

 

But the hint with the geared motor is a good one.

It leaves the gripper wheel or it’s drive wheel as last point of failure.

So I should swap the grippers between the two extruders and see what happens.

 

Edited by conny_g
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Posted (edited) · Bondtech extrusion issue?

I have now moved the gripper wheels of the right / second extruder to the left / first.

And I got a surprising result: I get the same inconsistent extrusion pattern!

See cam screenshot.

 

So it’s not the drive gears, it’s the motor gear or the motor.

If I seem to have observed that it’s in sync with one turn of the drive gear then it could not be the motor, given the motor turns 5 times as fast. The pattern would need to be much more dense if it related to one turn of the motor.

 

But to verify I could try a quick calculation how much material one turn of the drive wheel would extrude...

The drive wheel has a diameter of about 12mm, so it’s circumference is 12 x 3.14159 = 37,7mm.

That‘s the length of filament extruded by one turn of the drive wheel.

The volume of material is then 37,7mm x 6,4mm^2 = 240 mm^3.

If the layer height is 0.2mm that would cover a area of 240 / 0,2 = 1.202 mm^2.

If this was the first corner of my large rectangle that would form a right angled triangle with 2 identical sides of sqrt(2x1202)= 49mm.

 If the issue in the corner had a width of 50mm it would actually stretch across one quarter of the width of my object. Yeah, that’s about it.

 

So it’s an issue of the outer wheel of the planetary gear.

I need a new Bondtech geared stepper motor.

 

To verify I will swap the motors tomorrow and see if the issue is gone with the motor of the 2nd extruder.

 

 

 

 

38CBE2DE-1491-4B98-A39B-D6149F47824B.jpeg

Edited by conny_g

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Posted · Bondtech extrusion issue?

What about variations in nozzle-temperature? And thus variations in viscosity and flowrate? Where it would be just a coincidence that they happen at about the same time as a rotation of the gripper wheel?

 

Or for example, if the bed heats up (eating a lot of current) that this would shift the ground-level of the other signals, and thus influencing the measurement of the nozzle-temp? So it would adjust temperature not based on the real temp, but on an error due to shift in ground-level? Or something else along this line of thought?

 

If you swap motors and the problem swaps printers too, then it is related to the motor, of course. But if the problem would stay with the printer, maybe this or something similar could be an issue?

 

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Posted · Bondtech extrusion issue?

Bondtech responds upon describing the issue to them:
 

Quote

The center sun-gear is a part of the rotor in the motor, then there is 3 small gears around this that contacts with the gear on the shaft and the outside gear section.

I would ask you to dissasemble the motor, it is fairly easy for anyone with your skills to see if something has happened.

Also check so that the setscrew holding the primary gear onto the motorshaft is tight and is against the flat plane on the shaft, if it sticks out too far it will hit the secondary gear every rotation and this will force the secondary gear away loosening grip and this would show up as an underextrusion each rotation.

 

I'll take the motor apart tonight and have a look.
 

1 hour ago, geert_2 said:

What about variations in nozzle-temperature? And thus variations in viscosity and flowrate? Where it would be just a coincidence that they happen at about the same time as a rotation of the gripper wheel?

 

I'll swap motors and retest tonight and check the possibly defect motor.
I don't think it's nozzle temp. 1) it's too regular "in sync" with the rotation of the drive wheel 2) Why would that problem start now and I have never seen this before. Only if something changed or if a compontent on the mainboard went defect. Well... possible, but for me rather unlikely. But never say never. Let me do the test with the motors first, then let's see.
 

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Posted · Bondtech extrusion issue?

It seems I was on a wrong track and it’s not the motor!

 

Looks like it’s simply grinding / slipping of the filament due to too much pressure on the first layer!

After swapping the motor I noticed signs of the stripes again on the start of the first layer and took down the build plate a fraction of a turn of the adjustment screw and it got much better.

The pattern is still visible now, but only a little and I am convinced that’s just dirt in the drive wheel.

 

Thinking about how I got there I find that there’s probably two reasons for that.

 

First I had issues with clogged nozzles from certain filaments recently (it’s always tricky to switch from high temperature filaments back to PLA, now using separate nozzles) and I started to get used to overtightening the tension screw on the extruder. Which increases the grinding of the filament if it cannot move as it should.

 

And second I am printing 0.2mm layers in the moment where usually I prefer to print 0.1 and do that 90% of my prints. So I seem to have adjusted the build plate for 0.1 - I often do fine-tuning on that visually while the skirt prints.

That led to too much pressure on the filament during the first layer, to some decent grinding and just enough dirt in the drive wheels that the filament slips slightly each turn to release some pressure.

 

I did not find a lot of dirt in the drive wheel the last days or I would have thought of grinding directly. It seems it doesn’t need very much dirt for this effect. Once there’s enough dirt to reduce the grip in one position it’s enough to release pressure and no further grinding is needed.

 

Attached a cam still of the current print. The stripes pattern is much less, but still there. Next I will clean the drive gears another time, adjust the build plate properly, tighten the extruder pressure screw less and retry.

 

Another reminder that the build plate adjustment is key to 3D printing... 😉

 

 

EE35C3D9-A39D-41DB-8486-9158DB2E2B88.jpeg

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Posted · Bondtech extrusion issue?

After doing all this - cleaning drive gears, adjusting tension carefully, recalibrating the bed and increasing the print temperature slightly (for 0.2mm +10C seems reasonable, could also pay into this) - it's much better, actually totally acceptable.

The stripes still can be seen a little. 
But now looking at the other printer - where I haven't noticed that issue yet - I find that these minimal stripes are visible too.
So possible some form of this inconsistent extrusion on a large areas does possibly always exist, but is not relevant in most situations...
I need to check the bottom of the good prints I made with the other printer if they also have signs of stripes. And I would expect that they have.

 

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Posted (edited) · Bondtech extrusion issue?

In another iteration I find - or better:  I am reminded - that temperature is a key issue influencing the extrusion quality. In hindsight not surprising really, I should know. But it seems I forgot by developing bad "standard procedure" habits.


After dialling the temperature up another 15 C the striping disappeared completely and the dimensional accuracy is now perfect. While in the last round the stripes were much better and the dimensions of my lego struts 0.2mm too small.

 

I went up from 190 C to 215 C now. I wasn't aware that the ideal temperature differs that much between 0.1 and 0.2mm layer height. It seems that so far I haven't had a use case where quality with 0.2mm mattered that much so that I didn't notice the "few percent" of underextrusion of 200 C on 0.2 layers.


So bottom line, if you do these things right you will not get an underextrusion and/or grinding issue with 0.2mm layers:

- proper bed calibration so that the resulting distance is in fact 0.2mm and not less

- appropriate extrusion temperature

 

Edited by conny_g

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