Z-Motor stops moving

[kabanda 2]

Hi all,

I have barely used my UM2 (less than a week) and have what appears to be a serious problem.

I am printing something about 30 X 50 X 20 cm (W,L,H) . It is not complicated at all... a simple mechanical 2 dimensional block (as opposed to organic) there are only 90 degree angles.

When it reaches a height of about 8mm, it seems the z-motor stops advancing downwards and eventually the head starts grinding against the model.

I am very disappointing since I changed to this rather expensive printer from a kit one in order to not have to contend with such basic problems and concentrate on printing rather than repair. I also noted the emphasis on 'reliability' in the adverts.

Should I return the printer or does somebody know of a quick and 'lasting' fix?

 

[IRobertI 516]

I would start by turning the power off and then moving the bed up and down and check if there's an area with strong friction around that height. With the power off you can either lift the bed up by grabbing it as close to the back of the machine as possible and pull, or you can simply twist the z-screw (it's greasy though so be aware of that. At least it SHOULD be greasy, another thing to check).

Did you notice if it sounded like it tried to move the bed down at all?

If everything is moving smoothly then maybe there's something wonky going on with the end stop that makes it think it can't lower the bed anymore? Dunno, just thinking out loud.

 

[kabanda 2]

Thanks for the response.

Sorry in my post I meant dimensions 30 X 50 X 20 mm (W,L,H)

To my perception it did sound as if it is trying to move the bed down in the form of a momentary stepper motor buzz after finishing a layer.

I turned the machine off and lifted the bed passed the error point then let it free fall, it stopped at the error point but extremely little force was needed to allow it to continue. There is a bit of a click at the error point, but there are other similar clicks as it continues it's free fall downwards, it does not stop again for the rest of the fall.

For testing I made another model 20 X 20 X 20 and it seemed to go passed the point (Z direction) where three attempts of the model I am trying to print failed. This might at the very least remove possibility of end stop fault.

 

[gr5 2,069]

Could you photograph the part or what the model looks like in Cura? I'm thinking the Z screw is fine but there are other reasons to have the print head grind against the part.

 

[kabanda 2]

The image is at

www.myinfohome.com/height problem.jpg

See notes below

The images are more or less in chronological order starting from the back and moving towards the front.

 

• Furthest to the back are two identical Images of the failing print both having the error at exactly the same height.
  
• Next row forward a block of the same X and Y dimensions but without hole in the large horizontal plane (this reached about twice the height of the failing models before showing the same grinding).
  
• To the right of this is a small cube which went well passed the height of the failing models.
  
• The bracelet and pig were printed afterwards to see if there are any problems with orthogonal angles (they were both printed ok).
  
• More prints of the failing model were subsequently attempted using different combinations of resolution and speed but problem did not go away, and the failing height was identical.
  

 

[gr5 2,069]

You are showing us a problem I'm not sure that anyone has seen before.

1) What country do you live in? (This is an important question - but I don't want to explain why - please update your profile location to indicate your country).

2) So can you explain the symptoms again? Does the head knock the part off the bed? You say it's grinding into the part. Do you abort the print at that point? Or does the head just keep moving and moving with Z never moving and no more filament coming out? Or is it printing in the air? With the head above the part by a little gap but the filament isn't coming out?

3) If you hold the z screw while it's printing the "failing" area you could feel if the shaft is spinning a small amount between layers.

Depending what country you are in, you might want to return it but then you might just get another one that has worse problems. The shipping service is very violent to these printers. Usually you are better off fixing it yourself.

You might want to lower infill to maybe 5% or 0% just to speed things up so you can get to the failure point sooner.

4) I see you are printing with brim. Is that working? Or is the part lifting off the bed on the corners?

5) What is your: print speed, layer height, nozzle temperature? (these 3 numbers combine to let me know if you are printing at reasonable flow rates - knowing only 2 of the 3 numbers doesn't help much).

 

[kabanda 2]

1) What country do you live in? (This is an important question - but I don't want to explain why - please update your profile location to indicate your country).

Austria

2) So can you explain the symptoms again? Does the head knock the part off the bed?

No, maybe it would have done if I let it go on.

.

You say it's grinding into the part. Do you abort the print at that point? Or does the head just keep moving and moving with Z never moving and no more filament coming out? Or is it printing in the air? With the head above the part by a little gap but the filament isn't coming out?

Yes I abort as soon as I see the problem, it appears that at that point no more filament is coming out.

3) If you hold the z screw while it's printing the "failing" area you could feel if the shaft is spinning a small amount between layers.

I visually note a reference on the z-spindle, check it for change, I do not see it change.

4) I see you are printing with brim. Is that working? Or is the part lifting off the bed on the corners?

The brim is working ok and is not lifting at the corners.

5) What is your: print speed, layer height, nozzle temperature? (these 3 numbers combine to let me know if you are printing at reasonable flow rates - knowing only 2 of the 3 numbers doesn't help much).

I changed the speed from 50 to 150, layer height .1 to .25, temperature from Cura default (around 220?) to 240.

Notes.

1) While NOT printing this model I have successfully printed other organic models with all these combinations with predictable results i.e speed effected quality etc. Including extreme values on the same model for study.

2) Now the head is blocked and so I am truly stuck! The last time this happened I unloaded/loaded filament which fixed the problem but this time it is not working even after setting temperature to 260

 

[gr5 2,069]

260C will just make things worse as PLA at 250C and higher can slowly be baked into a difficult to remove gunk. I think it is caramelization.

180C is a safe temperature to leave the head for many minutes and warm enough that PLA is soft enough to remove and work with.

It's common for the head to hit the part due to shrinkage on the top warping the edges inward and lifting the corners especially. I'm just really surprised that the z screw would move part way and then not the rest. And only on some models. I'm not surprised at all that the head hits the part and not surprised at all that it stops printing. So I would be damn sure Z really stops and I would experiment with it using pronterface and set the Z to various values and watch the bed go up and down and see if it has trouble at some point. pronterface is very easy to use:

http://koti.kapsi.fi/~kliment/printrun/

 

Back to clogged head. There's lots of solutions.

The easiest is the "atomic" method described in extremely long detail here (but is very easy to do):

http://umforum.ultimaker.com/index.php?/topic/4118-blocked-nozzle/?p=33691

 

Altermatively combine that method with something that can fit inside the nozzle tip such as either hypodermic syringe or acupuncture needle.

Or the most reliable method and the most work - take the head completely apart and put the nozzle into some gas flame and burn all the PLA and teflon (from black feeder) out of the head (but not so hot as to melt the brass). Then soak in acetone for an hour, then put it back together and perform the atomic method until it comes out clean. I've only had to do this once.

 

[gr5 2,069]

By the way, printing at 150mm/sec .25mm layers with .4mm nozzle is (multiple the 3 numbers together) 15mm^3/sec which is way above what my UM2 can do and very few people have a UM2 that can achieve that throughput of plastic even at 250C. It is however possible with the right filament and a brand new nozzle, and brand new teflon isolator. You can see the results of printing at different speeds here and you can test your machine (after you unclog the nozzle) with the original test (that only goes up to 10^3mm - download it in the very first post):

http://umforum.ultimaker.com/index.php?/topic/4586-can-your-um2-printer-achieve-10mm3s-test-it-here/

Or the tougher test that goes higher here (again - first posting):

http://umforum.ultimaker.com/index.php?/topic/5436-a-tougher-extrusion-test-o/

 

[kabanda 2]

I managed to unblock the nozzle with an acupuncture needle one end and a small allen key the filament end.

since I seem to be able to print just about everything non-orthogonal of any height I was just wondering If someone has sufficient curiosity about this problem and a few centimeters of filament to spare who would be willing to print a 75mm X 58mm block and see if they can go past about 20mm height. I would be interested to know the results. :cool: