Weird "ribbing" on my prints

I can’t figure out what is causing this ribbing effect on my print. Config is attached. This is Lulzbot PLA printing at 185C, bed at 60C. I have two fans running, one is ducted and blowing on the print, the other is aimed at the extruder heatsink.

Any thoughts?
config.ini (2.92 KB)

How tight does the X axis belt feel? It should be kind of taut and yet still allow the bed to move smoothly. Looking at your Slic3r config, I noticed something: Your nozzle diameter is 0.35mm, but your layer height is set to 0.3mm. You typically want to set your layer height to less than 80% of the nozzle diameter, so less than 0.28mm. I would start at 0.25mm layer height. Your speeds look ok.

X-axis belt seems to be fine. It might be the layer height being set wrong, but I’m having a hard time believing that it would cause ribbing like this. Any other thoughts as to what might be causing this?

Yes, I’ve had this problem from the start and no amount of adjustment has made it go away. I think it’s interesting that, back in June, you mentioned the amount of play in your X linear bearings (under the Inconsistent Z leveling post). I’ve found that the plastic linear bearings can have a lot of slop in them. There was the comment that gravity should keep them in place, however the reality is that extruding plastic and bumpieness in the printed part can cause offsets in X and Y between layers if there’s play in the bearings.

I come at this with a background in conventional CNC machine tools where it is common knowledge that, the smaller and the more precise the part, the more mass and rigidity you require in your machine. In additive processes, mass is not quite as essential as you don’t need to resist lateral cutting forces. However, rigidity and dampening of resonances are still critical issues that must be dealt with.

I think 1013 ordered some conventional linear recirculating ball bearings to replace the plastic bearings. I’m not sure how that turned out but that is one of the directions I’m headed in now.

Yeah, I think I’m going to have to rip the machine apart and upgrade the bearings. I don’t suppose you know which ones should be used?

I’ve ordered some from ebay (shipping from China) Look at item 111015105791 or just search on LM10UU
I don’t know how freely they’ll function but I’ll report back when I get them. Coming from China, I anticipate that the preload lubrication will be too viscous so I’m prepared to solvent wash them and relube with a teflon based lubricant.
Also, I think it’s interesting that Makerbot just uses oil-impregnated bronze bushings. These travel as slick as anything but they won’t fit directly in the TAZ bearing mounts.

I had to replace my hot-end this past week (long story there, but not important)… while I had that apart I was just tired of the probably 1/16" of vertical and forward play that I had in the X axis… it was all from those IGUS (I think better termed I_SUCK) bearings.

The major problem with the ones that Lulz uses is that they are the ones that are suppose to be used in a “compression” not free floating. They - IGUS actually makes one that can be used in free floating applications. I didn’t try that, but may at some point.

Anyway, I had ordered some of the 10mm linear bearings from china and Ebay and so while I had most of the X AXIS apart I replaced the IGUS bearings with the linear ones.

WOW, why did I wait so long!!! I was able to get just about all the noise out of the system with a little playing with how and in what order I tightened the screws putting it back together… It look was was easily 10 thousandths or more probably closer to 20 out of the bearings and made it zero (or close to it).

After I got it back together, I dial calibrate checked the level of the X axis to the Y Axis smooth rods and tweaks just a smidge of difference out of that. Then I releveled the bed.

Now I need to make 1013’s other mods, but it was amazing the difference. Where I was wiping the nozzle before and you could just feel everything move forward and up, it doesn’t do that any more.

If they want to stay with the plastic bearings at least move to the ones that aren’t made for compression fit.

I’ve got enough linears to do all the other axis’s as well which I’ll do at some point in time…


Alan, I was looking back over your posts from June and caught your link to the IGUS data sheet. Incorrect part choice is definitely the root of the problem; these bearings would probably work great if they were pressed (like with an arbor press) into a non-deforming (like steel or aluminum) pillow block with the properly sized bore. There is no way they will be compressed to spec in an ABS housing of any type. Lulzbot might as well save a few bucks and just use some lengths of UHMW polyethylene tubing for their linear bearings - they would slide just as well and wouldn’t have as much slop!