Z-Ribbing, Noise on Ultimaker 2+

[ReallyBadDancer 0]

Hey all, 

 

I am experiencing some Z-ribbing after having corrected a layer-offset problem earlier this week on my Ultimaker 2+. The set screws on the belt pulleys had come slightly loose, resulting in prints that look like this. 

 

After tightening the set screws on all of the pulleys, this problem largely went away, although the printer now has a z-axis ribbing issue that wasn't there before. Now the surface of my prints has slight (<1mm), yet undesirable, horizontal ribs in both axes.

 

So prior to any of these issues (for the past 2 months or so), I noticed that the printer makes a slight squeaking noise that is a bit more pronounced in the y-axis. When I physically move the print head around, there is uneven resistance in the y-axis that increases near the center of the travel between the two extremes. Here is a video of the noise: 

 

https://photos.app.goo.gl/QYNZBZaztJ3jcARY6

 

Anyway, the noise seems to be coming from the back of the printer-- maybe the stepper motors? It's hard to pinpoint. It looks like they are impossible to get to without disassembling the printer. It looks like disassembly will also cause all of the axes to come loose from the guides. It looks a bit of a challenge to put back together, so I'd like to avoid doing that if it isn't the issue, but maybe there is a guide to doing this somewhere?

[IRobertI 516]

A picture of the "ribbing" would be helpful. Could be as simple as the z-screw needing to get a bit of a clean and re-grease.

 

As for the noise, more than likely it's the belts that are getting old and dry and need to be replaced.

 

Getting to the steppers is very easy, just remove the white metal covers, they're held in place by two screws, on from the back and one from the side.

[ReallyBadDancer 0]

Thanks @IRobertI, here is a picture of the same print from before the layer offset issue on the left (you can see the beginnings of it manifesting) and then on the right, after with z-ribbing.

 

The poor overhang quality on both prints seemed to be due to bed adhesion problems that I managed to solve from reading some forum posts here, and some temperature tuning. The Ultimaker is such an easy to use printer that I really didn't need to read much online before now.

[ReallyBadDancer 0]

Belt replacement: I guess both these

https://fbrc8.com/collections/ultimaker-2-spare-parts/products/sliding-block-half-um2-x8

and these? https://fbrc8.com/collections/ultimaker-2-spare-parts/products/timing-belt-200-x2

 

I have never greased the Z lead screw before (I lost the magnalube stuff, but I ordered more). Can you clean off the old magnalube with WD-40, iso alcohol and a bristle brush? 

[IRobertI 516]

It could also be that the z-bearings aren't sliding well on the z-rods so wipe those down with a cloth and maybe add a tiny drop of oil.

 

I would change the short belts as well while you're at it:

https://fbrc8.com/collections/ultimaker-2-spare-parts/products/timing-belt-200-x2

 

I've never really used any sort of solvent when cleaning the screw. I usually just move the bed up, wrap some cloth around the screw and then push the bed down. Rinse and repeat a few times. Then apply a bit of fresh grease and move the bed up and down a couple more times to spread it out.

 

See what the prints look like after that, hopefully that takes care of it.

 

It's also possible that it's inconsistent extrusion causing the lines to appear. It's one of those things where there can be several things at play.

[nighthowlers 2]

6 hours ago, ReallyBadDancer said:

Thanks @IRobertI, here is a picture of the same print from before the layer offset issue on the left (you can see the beginnings of it manifesting) and then on the right, after with z-ribbing.

 

The poor overhang quality on both prints seemed to be due to bed adhesion problems that I managed to solve from reading some forum posts here, and some temperature tuning. The Ultimaker is such an easy to use printer that I really didn't need to read much online before now.

 

This is super interesting. The image on the right looks very close to the issue I just resolved, however I would not suggest that is the cause because you had the printer working fine before you identified mechanical issues. My cause for prints like that was electrical and it would not just solve itself. It had to be there all along -- unless, power supply is degrading or is now being operated in much warmer ambient temperatures (causing wattage derating). 

 

Just for the heck of science.. can you reprint the same but with NO bed heat? Use Blue Tape to have the part stick.

 

 

Edited May 16, 2020 by nighthowlers

[ReallyBadDancer 0]

Ok, so I got the magnalube today, then cleaned and applied it to the lead screw. The z-ribbing is mostly gone, but the z-offset issue is back again. (sigh) I don't think it makes sense to further tighten the set screws on the pulleys, so maybe it's something else?

 

 

Also, there is some pretty gnarly warping happening. I noticed that in spite of having set the print material to PLA on the printer AND in Cura, the print temperature is sometimes going to 230 instead of 210 °C. No idea why that might be and didn't check this time, but it might be the cause of the warping.

 

Also added a drop of machine oil to the z-guides as well. 

[Torgeir 228]

Hi ReallyBadDancer,

 

You have several different problems for sure. So lets start with the first one you've mentioned, the bed warping and bad overhang. Your object have smaller footprint than the top part, this is the overhang in this issue, right?

 

The problem here is the fact that the overhang start directly from the heat bed. Heat from the close by bed plus nozzle is to much so plastic do not cool down and tend to creep down, this normally happen in this situation.

 

So cure for this is; either to print with blue tape (not using heat bed) or use a skirt that have a little distance from your object (say (1-1.5)mm) that is wide enough to shield the heat away from the overhang. Make sure that this skirt is wide enough say 20 lines or so.. Sometimes this is just not enough, so then to the blue tape.

 

Now to your other problem that's started with some loose pulleys.

The important thing to notice is the way you object is orientated on the bed, where is the front of you object pointing?

When we are looking into our printer, the "face" we see of you object is the front.

 

By knowing this, it is easy to see what your problem is. I can say it is not a Z or height issue as this only open up between layers without an offset in the X/Y plane. But only a X/Y offset can create such an error as shown here.

I think about a climbing belt on a pulley, this can create such an offset and make strange noise when printing. This can make noise just one way, or both ways.

 

When adjusting/tightening a pulley, it is very important to make sure that the pulley do not slide out of the position along the shaft!  Most often it is the short belts pulleys that's come loose, this due to the fact those four (4) pulleys are the ones carrying the highest torque when printing.

 

The important thing here is to make sure that the belts are strait, and that there is no offset differences between the two pulleys

going from each stepper motor up to the 8 mm long shafts.

First make sure that both X and Y stepper belt have no offset, good light and mirror is tools for this inspection.

 

When such thing have been on for some time, you might see remains from the belts in any of the corner that's tells something.

The long belts have to stay absolutely parallel (right above or below the shafts) with each axis (4 by 8mm). If one of the pulleys is offset center of axis, the belt will bend to one of the sides of the pulley when the (6mm) slider approach it.

 

This is the tips I'll hope work for you.

However, information about the orientation of the print object when printed will tell a lot about you problem.

 

Thanks

 

Torgeir

 

 

[IRobertI 516]

18 hours ago, Torgeir said:

use a skirt that have a little distance from your object (say (1-1.5)mm) that is wide enough to shield the heat away from the overhang.

Hmm... I'm not quite sure how this would work? A single layer of plastic directly on the platform will still be at the same temperature as the glass. I don't think I've ever heard this suggested before so I'm a bit hesitant to accept it straight off the bat.

 

 

Since you're seeing temperatures of up to 230C for PLA,  I would make sure the temperatures in the profile are actually correct.  A higher than normal print temperature and possibly bed temperature can cause both bad overhangs and warping. Or maybe you've chosen the wrong nozzle diameter in Cura? If you've chosen 0.6mm or more, then the 230C temperature is expected.

 

When it comes to the shifting, in my experience, 99% of the time this is due to loose pulleys on the motor shafts (or possibly that they are too far out on the shafts and rubbing up against the walls of the printer). While it's important that the axes are held in place and the belts run straight, I've seen printers produce normal prints with axes that are bouncing 1cm back and forth during the print, barely staying in the frame. So I don't think this is the cause in this case.

[ReallyBadDancer 0]

Thanks all, 

 

I got a decent small print out of the printer yesterday printing at 30mm / sec and with jerk / acceleration and temperature turned way down. Looking at the belts on the motors, they are definitely slightly worn. I got new replacement belts yesterday, so this weekend I am going to replace all of the belts and post photos of the old belts. I suspect that somehow at some point during the print the one of the y-belts is slipping, but I'll just replace them all.

 

I deleted all of my old profiles in Cura and rebuilt them, and the temperature issue seems to have gone away. There probably was some kind of an issue with the profiles I was using, although I couldn't detect any nozzle / temperature discrepancies.

[Torgeir 228]

Hi Robert,

 

On 5/20/2020 at 8:45 PM, Torgeir said:

use a skirt that have a little distance from your object (say (1-1.5)mm) that is wide enough to shield the heat away from the overhang.

Hmm... I'm not quite sure how this would work? A single layer of plastic directly on the platform will still be at the same temperature as the glass. I don't think I've ever heard this suggested before so I'm a bit hesitant to accept it straight off the bat

 

-----------------------

 

We know that the heat radiation from the bed can be quite directed to our print object and can degrade surfaces of our print.

But, by using a layer of filament at the bed surface around our print object, we can reduce the direct heat radiation. So by using this method the heat radiation will be spread over a wider angle and hence reduce the heat spot effect. Using this method may help, but will depend of the kind of the color chosen and thickness of this layer.

All this is from the "thermodynamics" that's been part of my job.

 

Thanks

 

Torgeir

 

[ReallyBadDancer 0]

The idea of the brim blocking the bed heat makes sense to me, although I do dislike removing it at the end- I hadn't tried printing it with a large offset from the print before though. I'll see if that makes a difference.

 

I did re-print a couple of the components from before with a large brim this time, and noticed that the warping had completely gone away. I also printed at 195C at 20 mm/s. This application is really warp-sensitive, so I don't mind the slow print speed.  Here is the resultant print from the slow print speeds, low temperature, new profile. I still saw a slight artifact in the y-axis though, so still replacing the belts this weekend.