Problems when printing vertical holes

[Julian2801 1]

Hey there,

 

I think I might have a mechanical issue with my UM3. 

 

As you can see in the picture the quality of the outer wall decreases at the height of the hole.

 

I already noticed that I had a bit of play on axles but I fixed it. But still, the problem remains. 

 

Does anyone have an idea about what is going on?

 

 

Edited September 21, 2018 by Julian2801

[gr5 2,173]

If you look at this area in cura layer view you can learn a lot.  Cura slices your part and each layer has "islands".  That hole adds an extra island.  Above and below the hole it's probably printing say left to right but just left of the hole it's reversing directions (or the other way around but either way it is probably going the other direction to the left of the hole - you can check in layer view and use the horizontal scroll to see for sure).

 

So that bulge to the left of the hole is probably related to changing directions and that implies to me you have a loose belt in the Y direction (assuming Y direction is through that hole).  How you could possibly get a loose belt on a UM3 is a mystery to me because normally all the belts have hidden tensioners inside the blocks.  But I'd check the Y belts.  If you put the head in a corner (important) and pluck them and check the pitch with a guitar tuner they should be 80Hz to 130Hz.

 

Anyway - check it out in layer view and see if I was right about the reverse direction.  Maybe I'm wrong and that's unrelated.

 

Oh - high friction can also cause this.  Put one drop (no more) of light oil (any light mineral oil such as 3 in 1 or sewing machine oil but not WD40 which is not an oil) on all 6 rods up in the gantry and push the head around to spread this.

[Julian2801 1]

28 minutes ago, gr5 said:

If you look at this area in cura layer view you can learn a lot.  Cura slices your part and each layer has "islands".  That hole adds an extra island.  Above and below the hole it's probably printing say left to right but just left of the hole it's reversing directions (or the other way around but either way it is probably going the other direction to the left of the hole - you can check in layer view and use the horizontal scroll to see for sure).

 

So that bulge to the left of the hole is probably related to changing directions and that implies to me you have a loose belt in the Y direction (assuming Y direction is through that hole).  How you could possibly get a loose belt on a UM3 is a mystery to me because normally all the belts have hidden tensioners inside the blocks.  But I'd check the Y belts.  If you put the head in a corner (important) and pluck them and check the pitch with a guitar tuner they should be 80Hz to 130Hz.

 

Anyway - check it out in layer view and see if I was right about the reverse direction.  Maybe I'm wrong and that's unrelated.

 

Oh - high friction can also cause this.  Put one drop (no more) of light oil (any light mineral oil such as 3 in 1 or sewing machine oil but not WD40 which is not an oil) on all 6 rods up in the gantry and push the head around to spread this.

1

Thank you very much for your quick reply. I've applied some oil (the unilube oil that was included with the UM3). The weird thing is, that I don't have any loose belts. I've tightened the short belts and checked the long belts.

 

I'm trying another print now and see how it goes.

[gr5 2,173]

1) Did you look at this portion of the print in layer view to see if it switches between clockwise and counterclockwise?

 

2) Check for play.  Push on the nozzle (gently) towards left, right, front, back.  It should not move.  Push and twist the head until it starts moving.  It should not move before the steppers start to move.  If it does - this is called "backlash" or "play".  There I gave you two things to do - please report back.

 

3) Maybe more photos of the issue above would help as well.  It looks like what you care about is only on the left side of the hole - is this true?  Can you photograph from a few more angles and look at the photos to see if the photos are showing the issue well?

 

[neotko 1,417]

On 9/21/2018 at 6:31 PM, Julian2801 said:

Thank you very much for your quick reply. I've applied some oil (the unilube oil that was included with the UM3). The weird thing is, that I don't have any loose belts. I've tightened the short belts and checked the long belts.

 

I'm trying another print now and see how it goes.

 

In my experience that effect always shows specially when the X/Y are out of square 

 

https://ultimaker.com/en/resources/19953-aligning-the-axles

 

 

[Julian2801 1]

10 hours ago, gr5 said:

1) Did you look at this portion of the print in layer view to see if it switches between clockwise and counterclockwise?

 

2) Check for play.  Push on the nozzle (gently) towards left, right, front, back.  It should not move.  Push and twist the head until it starts moving.  It should not move before the steppers start to move.  If it does - this is called "backlash" or "play".  There I gave you two things to do - please report back.

 

3) Maybe more photos of the issue above would help as well.  It looks like what you care about is only on the left side of the hole - is this true?  Can you photograph from a few more angles and look at the photos to see if the photos are showing the issue well?

 

1) Yeah, you are right about the changing direction. I think the hole was in the x direction. That also fits with my observation that when I pluck the front x belt the frequency is about 310 Hertz ( I'm assuming that this means it is too tight?)

 

2) When I gently push the nozzle of the printhead in any direction it isn't moving. When I'm moving the whole printhead it is in sync with the stepper movement.

 

3) So after I eliminated the play on the axles it got a lot better. But still, there is a small imperfection. The imperfections are only on the layers where the hole starts and ends. I will wait if you can say that the front x belt is too tight and then try again. If the issue still is the same I can send you more pictures if you want.

 

 

[Julian2801 1]

5 hours ago, neotko said:

 

In my experience that effect always shows specially when the X/Y are out of square 

 

https://ultimaker.com/en/resources/19953-aligning-the-axles

 

 

1

 

I also thought of that. But I checked it and everything is in a square.

[gr5 2,173]

310Hz when the head is in the corner?  I... don't think so.  Try making a 5 second video please - I want to hear it.  Put the speaker so close the belt almost touches the speaker.  I'm talking about the long belts - not the 2 short belts.  Those should also be tight - 310Hz for the short belts may be fine actually.

 

If you can show better pictures of the part in the area of the problem.  Is it sticking out more?  In more?  

[Julian2801 1]

 It is making 120Hz on the long belt when the head is in the back left corner. I tried it another time now. Maybe my app wasn't really accurate

Edited September 24, 2018 by Julian2801
Tried plucking a second time

[Julian2801 1]

The pictures now are from a different model but they are showing the exact same problem. As you can see when the hole occurs the outer layer goes into the model. As you can also see the outer layer quality isn‘t really good.

[Julian2801 1]

I think that the problem also occurs when the printer is doing the 100% infill for the 10 layers on top

[gr5 2,173]

2 hours ago, Julian2801 said:

 It is making 120Hz on the long belt when the head is in the back left corner. I tried it another time now. Maybe my app wasn't really accurate

Okay good - that's normal.  Did you try both sides of all 4 belts?  (8 tests)?  I suspect the belts are fine anyway.

 

when you pluck a belt it's best to pluck in the center as that limits the over tones.  If the primary frequency is 120Hz then there will be also frequencies at 2X 3X 4X 5X 6X 7X etc but those are fainter.  So 240HZ or 360Hz would be what are called "overtones".  The tuner app is supposed to ignore those but it has trouble hearing tones below 200Hz I think (possibly the microphone sensitivity falls off).  Or maybe the rubber belt just isn't an efficient way of transmitting lower frequencies to air.

 

[gr5 2,173]

So in the very last photo the right edge looks worse than all the other 3 corners visible.

 

I'm thinking that is probably the "z seam" which is a bad name - basically where the layer's outer shell starts and ends - for those layers where that edge sticks out more.  Could you confirm that in cura layer view?

 

So make sure coasting is off and I'd turn off "outer wall wipe distance" to see if that helps.

 

The other thing to try - I may have already mentioned this - is to cut speed in half and lower temperature by 10C just to see if that helps.  Even if it's not a good final solution it may lead you to new ideas.

 

[gr5 2,173]

Also maybe set all the printing speeds to the same speed and set them all to 35mm/sec just to see what happens.

 

If inner shell is higher speed than outer shell then you can get a bit of overextrusion when it switches to the lower speed because it takes a while for the pressure to equalize in the print head.

[Julian2801 1]

I can confirm that this is the section where the z seam occurs. My infill speed is 50mm/sec  and outer and inner wall speed is set to 20mm/sec. Im printing at 0.1mm layer height at 205 degrees Celsius. I'm starting another print now and see if that helped. 

Edited September 24, 2018 by Julian2801

[Julian2801 1]

As you can see the lowered print speed helped quite a bit. The holes nearly dont have a visual effect on the outer layer anymore.

 

But apart from the hole problem there are still tiny imperfections as you can see. May this be caused due to the fact that my spool is nearly at the end?