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ivanchaos

Wavy pattern appears along Z axis of print

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Hi Everyone:

 

I've encountered a rather strange problem: My print results appears to have wavy pattern along their z axis. I know it sounds like a z rod problem but I've checked more than ten times and ruled it out.

 

Another thing about this phenomenon is that somehow it's related to print speed:

test print

 

 

It bothering me since the wavy pattern is visually noticable and to be honest very obvious...like this one:

naked women bust (with wavy pattern along z axis)

Any ideas about this guys? Any help would be much appreciated!

 

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Another idea is to check your filament tension. Maybe wavy pattern corresponds to the oscilating movement of the filament spool while unrolling. With too much tension this could affect the flow rate.

 

Hi Nicolinux, I checked the filament spool, the tension needed for unrolling it is very subtle, pretty much sure it's not the reason...

 

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Looking at your picture again, I am pretty sure it is somehow related to the fluctuations in the flow rate. There are wider slices followed by thinner ones. So the nozzle pushes out variable amounts of filament every few layers. And although variable the changes are still recurring.

Maybe the connection between the z-stage and the acrylic bed is a bit loose. Maybe one of the springs got stuck and it allows the bed to move slightly.

 

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This is very bizarre. This experiment where you printed slower and faster blows out all my theories (filament gets wider and skinnier, Z screw issues, slicer issues). Maybe you should repeat that experiment in reverse in case the problem had nothing to do with the speed and it was a coincidence.

Anyway, assuming it really changes with speed the only thing I can think of is temperature. The time it takes to go from 210 to 190 is much too fast to make any difference in the pattern.

The problem is most likely related to flow of plastic. It's extruding less in the skinny sections and more in the fat. Temperature cycles explain this perfectly. Print using the cura window instead of the Ulticontroller and look at the graph of the temp. Time the bumps/waves in the temperature graph and also time how much time it takes to print from one "bulge" on your part to the next. See if they roughly agree.

Also to eliminate fan issues you might want to turn it off as an experiment.

I would recalibrate the PID values. Actually I would get pronterface and figure out what the current values are. Pronterface is free. When it first connects to your UM it prints out lots of values including the PID values. You can see my values in this screen shot:

Pronterface Screenshot

 

Oscillation is very common in PID controllers. Larger values of P or I increase oscillations. D decreases. I wouldn't touch D though but it is quite safe to cut P or I (or both) in half. The only downside is it may take a little longer to heat up but probably not. Or you can issue the M303 to recalculate the values:

M303 S210

 

210 is the temp to calcluate the values at. Default is 150C and 210C will give you slightly better results (not much different though).

 

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I've had this and I'm pretty sure it is caused by a combination of temperature and perhaps particular fibre type. I've been printing at 220 degrees with some Faberdashery fibre and getting good results, although my layers were sometimes a bit uneven.

Today I put in some ColorFabb fibre and used the same gcode with very uneven results. At 220 the ColorFabb PLA seemed to be a lot more runny and this made it harder for the printer to control how the layers were laid down.

I dialled the temperature down to 200 and printed again with much nicer results. I started using higher temperatures in the first place to improve adhesion to the base, but 200 sticks fine and I'm getting much smoother layers.

I'd advise you to drop the temperature as low as you can, I reckon that will solve your problem.

 

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This is very bizarre. This experiment where you printed slower and faster blows out all my theories (filament gets wider and skinnier, Z screw issues, slicer issues). Maybe you should repeat that experiment in reverse in case the problem had nothing to do with the speed and it was a coincidence.

Anyway, assuming it really changes with speed the only thing I can think of is temperature. The time it takes to go from 210 to 190 is much too fast to make any difference in the pattern.

The problem is most likely related to flow of plastic. It's extruding less in the skinny sections and more in the fat. Temperature cycles explain this perfectly. Print using the cura window instead of the Ulticontroller and look at the graph of the temp. Time the bumps/waves in the temperature graph and also time how much time it takes to print from one "bulge" on your part to the next. See if they roughly agree.

Also to eliminate fan issues you might want to turn it off as an experiment.

I would recalibrate the PID values. Actually I would get pronterface and figure out what the current values are. Pronterface is free. When it first connects to your UM it prints out lots of values including the PID values. You can see my values in this screen shot:

 

 

Oscillation is very common in PID controllers. Larger values of P or I increase oscillations. D decreases. I wouldn't touch D though but it is quite safe to cut P or I (or both) in half. The only downside is it may take a little longer to heat up but probably not. Or you can issue the M303 to recalculate the values:

M303 S210

 

210 is the temp to calcluate the values at. Default is 150C and 210C will give you slightly better results (not much different though).

 

Hi gr5:

I've ran a test using Pronterface, the chart is exactly the same as yours, so I guess it's not the problematic spot?

 

I've had this and I'm pretty sure it is caused by a combination of temperature and perhaps particular fibre type. I've been printing at 220 degrees with some Faberdashery fibre and getting good results, although my layers were sometimes a bit uneven.

Today I put in some ColorFabb fibre and used the same gcode with very uneven results. At 220 the ColorFabb PLA seemed to be a lot more runny and this made it harder for the printer to control how the layers were laid down.

I dialled the temperature down to 200 and printed again with much nicer results. I started using higher temperatures in the first place to improve adhesion to the base, but 200 sticks fine and I'm getting much smoother layers.

I'd advise you to drop the temperature as low as you can, I reckon that will solve your problem.

 

Hi Robmiles:

I tried the lower temp trick til the machine underextrude and the print fail...but no luck.

 

Looking at your picture again, I am pretty sure it is somehow related to the fluctuations in the flow rate. There are wider slices followed by thinner ones. So the nozzle pushes out variable amounts of filament every few layers. And although variable the changes are still recurring.

Maybe the connection between the z-stage and the acrylic bed is a bit loose. Maybe one of the springs got stuck and it allows the bed to move slightly.

 

Hi Nicolinux:

I've checked and re-assembled the z-stage with z-rod connection a dozen times, they are tight and secure. Besides if the problem do relate to z-system, my re-assembling should make the rest results vary, but sadly every individual test are identical.

 

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What speed and layer height are you printing at? Given that everything else has been ruled out, my guess would be that it's related to head pressure; the pressure builds up, so the filament starts to slip causing under-extrusion; the pressure evens out, the filament grips again, pressure builds back up and the cycle repeats.

 

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so the filament starts to slip causing under-extrusion;

 

That would make sense but he has the problem even at 10mm/sec! And it's not any better at 10 then at 20. No -- I think it's temperature related.

Please please - use Cura - set the temp to 180C and let it sit for 20 minutes. Come back and look at the graph. This was what I wanted you to do the first time. This is what Robert suggested. This was the VERY FIRST SUGGESTION and it's the only one that makes sense to me at this point.

I spent a lot of time thinking about your issue. Did you spend much time reading all the responses and thinking about them?

 

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Ah yes, I forgot that he was using very low speeds. I wonder if that's the problem somehow... the nozzle is dwelling on the print, reheating it, causing it to soften and sag away from the nozzle a bit, reducing the heating... you can see on the sides of the print that it is bowing out.

Printing faster might alleviate the reheat, but then you get into too little layer cooling issues. I'd suggest trying printing several test pieces at once, at the same speeds, and see if that improves the quality.

 

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A static test like that could be good for keeping variables out but I don't know if letting it just sit there is going to make the temperature sway much. Stagnant air and no cold material makes it pretty easy to keep a constant temperature, add in fans and cold material and it might start to struggle more and produce dips.

edit: This was in response to gr5, illuminarti snuck in between. I really need to stop doing more than one thing at once...

 

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