Wave-like or deviated layers in print

[Horia 0]

Hello guys/girls, this is my first question and I hope I am posting in the propper forum.

I am running tests on my PowerWASP EVO (custom Marlin firmware from WASP project) and using CURA 15.04.4 as slicer.

My problem is this:

I see a pattern of misaligned layers (wave shapes) on the shell (outer perimeters) layers. Tried a lot of different settings, didn't go away.

Picture:

I used the same filament (PLA Creator series filament) on Creator Pro (used Simplify3D slicer), done the same tests and the prints were ok.

Is this a hardware problem or more likely something to do with the slicer?

Also I printed test from the WASP team model library. I can't see the waveform but I don't know if it could appear in this model (cause of the round curves).

Edited February 2, 2016 by Guest

[gr5 2,270]

Measure the distance between waves as accurately as possible (measure many waves and divide by number of waves). Then measure the screw thread pitch as accurately as possible (how far does the Z axis move up or down with one full turn). Are they the exact same distance? probably. Maybe your Z screw is warped/tilted or bowed.

What happens is the Z distance is moved farther than average for part of rotation and then less than average for the rest. This means some layers are slightly closer together and they get slightly too much plastic and it squirts out thicker so you get thicker walls. Then the Z axis moves faster than normal and you get thinner walls. It's very subtle on the Z screw but it shows up visible on layer thickness.

[Horia 0]

Measure the distance between waves as accurately as possible (measure many waves and divide by number of waves).  Then measure the screw thread pitch as accurately as possible (how far does the Z axis move up or down with one full turn).  Are they the exact same distance?  probably.  Maybe your Z screw is warped/tilted or bowed.

What happens is the Z distance is moved farther than average for part of rotation and then less than average for the rest.  This means some layers are slightly closer together and they get slightly too much plastic and it squirts out thicker so you get thicker walls.  Then the Z axis moves faster than normal and you get thinner walls.  It's very subtle on the Z screw but it shows up visible on layer thickness.

 

I will try first thing tomorrow to measure the layers and compare them to the thread pitch.

As I was reading your reply I remembered that I saw the left Z screw have a little wobble while I was printing.

Sure hope it's not a mechanical problem.

[Horia 0]

I verified if the machine rises 1mm when I move Z axis from software.  It does (roughly measured) but I can't accurately verify that without disassembling it. I won't do that because I will lose my warranty. If it is a mechanical problem I will address the manufacturer but first I want to rule out the other possibilities (software/ firmware).

I have here some videos of the Z rods moving:

Left Rod (some wobble here):

https://drive.google.com/file/d/0B_jwSVrnQA08TS1jcFo0RE1abjA/view?usp=sharing

Right Rod (can't see wobble):

https://drive.google.com/file/d/0B_jwSVrnQA08YmZfU3lDU2JCMGM/view?usp=sharing

Is wobble the culprit?

Edited February 3, 2016 by Guest

[gr5 2,270]

The errors are too small to measure the error that way - if you move it 1.000mm it will probably move pretty close to that - maybe 1.010mm - that's enough error to see your wave problem but too small to measure. If you move 10mm, the problem is invisible because the error goes back to zero on a regular repeating pattern.

Did you measure the distance between threads on the z screws? Is that the same distance between waves?

Try this - print a small hollow cube near the left z screw and another one near the right z screw. If the left rod is bad but the right rod is good then you will see the wave pattern on the left cube but not the right cube.

[Horia 0]

The errors are too small to measure the error that way - if you move it 1.000mm it will probably move pretty close to that - maybe 1.010mm - that's enough error to see your wave problem but too small to measure.  If you move 10mm, the problem is invisible because the error goes back to zero on a regular repeating pattern.

Did you measure the distance between threads on the z screws?  Is that the same distance between waves?

Try this - print a small hollow cube near the left z screw and another one near the right z screw.  If the left rod is bad but the right rod is good then you will see the wave pattern on the left cube but not the right cube.

 

So, here are my results:

1. I measured the distance between the threads of the Z screw and my caliper indicated 1.42 It is very hard to measure without disassembling it.

2. I measured the distance between the most outer layer and the next most outer layer and it had a distance of 1.2 mm at 0.1 layer hight.

There are 4 layers outwards and 4 inwards.

3. I printed the hollow cube on each side of the bed (10% distance from from the edges):

0.1 layer

02. layer

At the 0.2 layer thickness hollow cube you can see the 4 layers going outwards been squished and the other 4 facing inward being progressively squished.

The left one is printed on the left side and the right one on the right side.

It seems that the left waves are a little more sharp.

Thank you for the help.

Edited February 4, 2016 by Guest

[gr5 2,270]

You didn't measure with the caliper the best way. The best way is to measure as many waves or threads as possible and then divide by the number of waves or threads. This gives you a more accurate result. That's what I tried to explain earlier.

With your less accurate measurement I would say that 1.2= 1.4 to the accuracy of your technique and this is indeed a bad Z screw. It sounds like the left Z screw is worse but they might *all* be bad. I don't know any good way to test a Z screw other than to print a hollow cube and look for the waves.

[Horia 0]

You didn't measure with the caliper the best way.  The best way is to measure as many waves or threads as possible and then divide by the number of waves or threads.  This gives you a more accurate result.  That's what I tried to explain earlier.

With your less accurate measurement I would say that 1.2= 1.4 to the accuracy of your technique and this is indeed a bad Z screw.  It sounds like the left Z screw is worse but they might *all* be bad.  I don't know any good way to test a Z screw other than to print a hollow cube and look for the waves.

 

Sorry, up until your last reply I didn't understand exactly the method you were talking about.

I measured 10 threads and the caliper indicated 14.09 mm.

I am convinced now the left Z screw is the culprit and probably the right one (but much less).

Thank you for the help, I will update the thread when the manufacturer responds.

[Horia 0]

The rods were somehow bent in transport. The printer is now in service.

Thank you gr5 for the support offered.