Z-axis artifacts (wobbling, irregularities, waves, ribbing)

[mmark]

Hi there!

I’ve got my printrbot quite sometime now - a Jr v2
As a good printer behooves - I’ve modified my far share on my printer.

my setup

Only, one thing I don’t seem able to fix; a wave pattern in my prints due to an irregularly in the z-axis which has become worse with time.

from flat to irregularitiesSince I got my printer I’ve noticed that the y-axis was not entirely leveled. I fixed this as good as possible but never seem to get rid of it. It wasn’t that much of a problem since I compromised it with the bed leveling.

_x-axis not level by 2mm_I’m not entirely sure if that something has to do with it. It could though - as you can see on the image below. The Jr moves it’s extruder on a cantilevered platform connected to the z-axis. On the first image you can clearly see the wobbling pattern. To print this side of the object the y-axis has to be extended more than the other side; the image blow that. Here you can clearly see a decrease in the wobbling pattern. When the y-axis is extended, the weight of the extruder could become more of an issue because it amplifies any minor irregularities of the z-axis or minor movements. (Right?)

a lot of irregularities

almost flat

That is my theory at least, but after some research I found this interesting article with many more causes. [www.evernote.com/shard/s211/sh/701c36c4-ddd5-4669-a482-953d8924c71d/1ef992988295487c98c268dcdd2d687e]

In short:

- ‘misalignment of layers in a repeating pattern with a period equal to the Z thread pitch’. English is not my mother tongue so I have some troubles understanding the technically. heheh Does that mean that the rod isn’t aligned exactly with the stepper motor axis?

I’m doubting if this is my case since I’ve two smooth rods guiding the x axis. However, that didn’t prevent the x-axis to be not level…

- Z ribbing, ‘“rounding error in the number of steps per layer causing some layers to be shorter or taller than others”. It has to do with the stepps of the motor and the type of threaded rod. - not my case I think. But to be fair, does anyone exactly know what kind of threaded rod (the pitch) with the Jr v2 is used? I know it isn’t your normal M8
- Constraining by wires etc, they create a resistance by with the axis can more probably. - No.
- Spool pulling against the extruder, which will tend to lift it. My spool can move freely, but it can’t hurt to make a better one.

Extra tip: run the filament through a low-friction tube - this can make quite some difference according the article. So I’m going to get one anyway.
- filament diameter is not uniform round causing thin and wide layers. - mine is okay
- A tip I found here on the forums: wobbly table (not the issue in my case). - mine is okay

The main strange thing about mine particular issues is that one side of je object is fine, almost flat - the other side has a strong wave pattern. However, the pattern is regular…

from flat to irregularitiesI guess it’s kind of an experiment to fix this, so I was wondering if you had any experience, ideas or thoughts on this

Every tip is welcome!

Thanks, Mark

[mmark]

Forgot to say: When the z-axis moves, I can see that it has a little ‘swing’ at the top. However, since my the z-axis has to smooth rods to guide them, I don’t expect that that is the reason?

[Antonio_Bencini]

in the past i have a problem like yours

i have solved simply verifing the amount of material extruded, i know seems impossible but i solved with a correct extruder amount of material

[Mike_Kowalczyk]

Also have seen this issue on some printrbots, just not as pronounced. Anyone have a solution?

[mmark]

Thanks for you reply,

I’ve checked my cura settings and the filament diameter - everything seems correct.

[Antonio_Bencini]

try to extrude 100mm manually and measure the real amount of filament extruded

[INVENTion]

I’ve had the same problem and I’ve reduced it, originally, using Simplify3D software. However, it is still there.

I’ve read somewhere it has to do with the threaded rod. Mine is pretty wobbly so first thing is to try to make the z screw the most straight it can be.

[Bigsean1225]

What layer height are you printing at?

[jesseslone]

I’ve had this problem before, and I think the reason Antonio_Bencini is mentioning it is because it becomes more pronounced with over-extrusion, which it looks like you have a little of. I find that I run an extrusion multiplier around .898 and I get much less of it. The last time it was bad on one side for me, it was because my Y belt was loose, so that would be my next step, to double check the x and y belts, as well as the stepper mounts. I have wobble in my Z-screw as well, but those things usually take care of it. The next step would be to adjust the layer height to something directly calculated from the steps and pitch of the acme screw. I know for my Simple Metal it works out to something like .1975 or something like that. I think you’ll see the most improvement by fixing the over-extrusion though.

[ianadan]

Hi Mark

You say this is getting more pronounced over time, so I guess we’re looking at a little Wear and Tear here as well as a few other things. I also have a Jr v2 (amongst others) and it’s a good printer when on form.

You may want to print something to keep the Z rods from moving as the Z goes higher. The 8mm rods are fine but they can flex as there is more torque on them.

Tighten all the screws. If you find one a bit loose in the wood, treat the threads with wood glue, screw them as far as they will go and then, when it dries, turn it a bit more - it should help the grip again. If you think the wood maybe too worn, and you have access to a laser cutter, the complete DXF are available on youmagine.com, as are lots of PB original wood plans.

The Z screw is a 3/8" ACME screw. I’m sure there are some tables that will tell you the optimal layer height.

As mentioned before, check all the belts. Tight but not overtight as the motors will suffer, especially on the Y and X when they bend round the bearings.

Ian

[mmark]

Don’t you check the stepper calibration if you measure your prints?

[mmark]

I’ve noticed the same with mine actually… I think its time to replace the wooden thing witch Printrbt supplied me with - any good alternatives?

[mmark]

between 0.1 and 0.25

[mmark]

Or do you mean like this?
http://help.printrbot.com/Guide/How+to+Calibrate+your+Printer/81

[mmark]

like so?
http://help.printrbot.com/Guide/How+to+Calibrate+your+Printer/81

[mmark]

Hi, thanks!
The wooden coupler witch needs to hold the 3/8" ACME screw attached to the motor is not the most sturdy one. It allows the 3/8" ACME screw to slide sideways easily.
Also, I’ve noticed that the white nylon (?) thing (the one witch is threaded) can be moved (~0.5 - 1mm) back and forward.

Is there for both a good alternative?

Cheers!

[jesseslone]

What happens if you go up to a 0.3 layer height, is it more or less visible?

[Antonio_Bencini]

here is easier

[jesseslone]

Edit: This is not in response to the Video:

That is one way, but with different filaments you always have slightly different diameters. I was referring mainly to slicer settings, where the extrusion multiplier is. In cura, it’s called the “Flow Multiplier”. I would recommend printing something like a 10mm cube and reduce the multiplier by .02 over a few prints and see if that helps. If you are over extruding, and you calibrate the printer steps for x and y with a test print, the values will be inaccurate. I run test prints with the filament until I start to see evidence of under-extrusion, then back off a little.

[mmark]

looking at the Octo’s in that video my problem should be underextruding… Wil try non the less!