Minor but Consistent z layer artifacts Help?

[Tyler1 0]

Hi, I've had my printer for about a 2 months now (Ender 3). Oh yes, I know this is an ultimaker form but I sadly can't afford one. I do use cura so I decided to post here. Anyway I've had issues with these odd z layer lines on my prints they always occur at the same place.

 

Image: https://imgur.com/a/EHHjSNB

 

Things I've done so far: 

1. I checked to see if my 8mm threaded z axis rod was bent. I sat it on a table and it was every so slightly bent, maybe .07 mm of bend. I find it hard to believe that that could actually cause my issue.

2. I've checked the alignment of my z stepper with the cuppler and rod. No issues there they rod slides in and out with ease when screws are loosened.

3. I checked the alignment of my frame on my machine. Everything is square within .1 of a mm. All screws are tight too.

4. I checked the belts on the x and y axis of the printer. Both are very tight and make a medium pitch sound when plucked like a guitar.

5. I checked my rollers and all rollers are tight but not too tight. I can still manually spin them with my hands.

6. I've checked the tension on the z 8mm threaded rod, the screws are snug but not all the way tightened down.

7. I've tried printing with heat off incase my of any bed heating issues, very minimul improvement.

 

Other info: My z 8mm threaded rod is free floating and does not have a bearing at the top. My only other mods I did was add a bltouch and a 5015 petsfang. I print on glass at 210 degrees for pla.

 

Going back to the z 8mm threaded rod as an ending note here. If I disconnect the z stepper cable and push the x carriage down really fast, I do notice that the top of the z rod wobbles just a little bit. 

 

I think I've tried everything here, that's why I'm posting. Could that .07 mm bend in my z rod actually cause the issue I'm seeing. Is that slight wobble actually my issue. If so where could I buy a rod that would be 100% straight unlike the one I have? 

 

If I forgot anything please let me know also sorry for any typos or errors. 

 

Thanks .

 

[gr5 2,173]

A bend in the z rod or wobbling will create a smoother, harder to see, wave like pattern.  Your issue is different. 

 

What happens in your case is that the bed isn't always moving a consistent amount - it gets stuck a bit and so it over extrudes a layer (not enough space for the plastic extruded) and then on a later layer (sometimes the next) the bed moves the full amount of all previous desired moves that were incomplete and you get an underextruded layer.

 

One thing to try is to add a brick or some heavy object so that when the Z screw rotates the bed is more likely to come all the way down and rest on the threads once again (or if it's your print head that goes up then a weight can help wilt that also).

 

Usually the fix is to clean the Z rod.  If you want to do an extra good job, then remove it completely (typically the stepper is attached which is fine) and then clean it with wd-40 and tooth brush and dry completely with rag or paper towels.

 

I'm not sure about lubrication.  Ultimaker recommends a particular grease (don't know the brand or anything) and they recommend oil for the straight rods (no oil on threaded rods).  I don't understand the logic of these choices at all.  If you have a fancier, more expensive Z nut (like $3 instead of $0.50) then it should have ball bearings inside and you probably don't want any grease or any oil (as this collects dust in with the ball bearings).

 

 

[Tyler1 0]

Thanks @gr5 for working with me on this issue! I took the z axis rod off and made sure to clean it well. I did notice some dirt on it. When I was done it was very clean. I sprayed it with silicon. I reassembled the machine and added a weight to the x gantry. The heaviest weight that I could find that I could put on the machine was a 100g weight. I also noticed that the x gantry was hard to move up. I noticed the rod tension screws were super lose so I tightened them not too much and the x gantry moved up much smoother.

 

The results didnt appear to be much better.

Was the 100g weight not enough?

 

Also, I failed to mention that anything I print out always comes out .2 to .3 mm shorter than it should. I really don't know why this happens. I suspected a very squished first few layers. But after setting my z offset higher (-2.4 down to -2.3) I still got the same results .2 to .3 mm too short.

 

Thanks!

 

[gr5 2,173]

Can you show what's on the Z axis?  is it a print bed or is it the print head?

 

I think the 0.2mm is normal for Z height error.  That probably just means you are squishing the bottom layer a lot.  That's good so that your parts don't come loose during printing.

 

100g of weight?  I was thinking more like 1 or 2kg.  Do you have exercise weights?  Hand weights?  Bricks?

 

[Tyler1 0]

Thanks @gr5 for the replay again! I attached a picture of the machine. The print head and extruder are attached to the bar and the bar raises and lowers with a single a axis rod.

 

I didn't have any 1 kg weights, so I made a temporary one. It's about 1.2kg. I made it out of change and zip tied it to the side of the x gantry.

 

When I added the weight I also noticed that the x gantry falls by its self and stops about 3mm short of hitting the bed.

 

I reprinted the same square and it was identical to before with a small improvement. However, I still notice a few lines that look really bad especially towards the top.

 

My extruder has been calibrated. It was set to 1 for this print as for all the others too. I thought that it might be over extruding but I printed out a cube with a single wall and the wall measured .47 to .49 mm. My line width was set for .48.

 

Thanks!

Edited October 15, 2019 by Tyler1