Initial layers poor perimiter

The printer is doing some very nice work, but one aspect that I haven’t got to grips with is how to make the first few layers without the outside edge being rather ragged looking. I have tried printing with a fine layer height (0.1mm)and it produces a very fine surface finish once it has printed the first mm, but up to then even with a chamfer it still has that stringy squashed look.

What tips do you have for reducing this?

Cheers

Les

pics?

Hard to know exactly what you are describing without pictures. But “first few layers… ragged looking” and “stringy squashed look” both make me suspect you are either too close to the bed, and/or are over-extruding. Based on that, I would recommend:

  1. Measure your filament diameter accurately and enter it into your slicer before slicing the model.
  2. Calibrate your E-Steps. There is a guide in Lulzbot’s support section, and many discussions here on the forum with instructions on how to measure filament travel and adjust your machine’s stored E-Step value.
  3. If the problem persists after #1-#2, then add a little negative Z-offset – either in your slicer, or via the M851 command.

If none of those resolve it, post some closeups and a further description and people will be able to jump in with better analysis.

here’s an image guys

http://i1380.photobucket.com/albums/ah183/lesthegringolesthegringo/20170117_075452_zpsksd4qxc8.jpg

cheers

Les

Do you have any close-ups? I can see a texture change there, and I assume the top (in the photo) was the bottom of the part as printed. It would be helpful to see a close-up of the vertical edge, and of the bottom; close enough we can make out the individual extrusion layers on the edge and the extrusion pattern on the bottom layer.

I would normally say roughness on early layers is from starting too close to the bed or over-extruding the first layer. And that would still be my first corrective action – add perhaps 0.05 to 0.10mm positive Z-offset (i.e., reducing the magnitude of your negative z-offset) to start slightly further way from the bed.

But the abruptness of the change is puzzling (i.e., it appears to go from “rough” to “smooth” at one particular layer, rather than gradually). Do you have any fan or temperature changes that occur at a specific layer? What material, and what bed temperature?

I’m using Proto-Pasta ABS, 275 deg nozzle, 110 bed temp, and utilising standard Cura settings apart from layer thickness and initial layer height, which I have reduced thinking it may help with the initial layer issue; perhaps I have made it worse?

Les

What I would try…

  • I think the default Cura profiles have first layer as 0.425 thick. You can go less than that, but I would recommend at least 0.20mm, as it gives a little more tolerance for bed level compensation. (Really thin first layer requires PERFECT bed level compensation.)

  • Change the Cura “Initial layer line width” to 100%. (The default is 125%, which extrudes additional plastic. That, coupled with the negative Z-offset in firmware, is intended to provide great bed adhesion – but often means too much plastic on the first layer.)

  • Reduce bed temp to 100C. (Only raise it back up to 110C if you have trouble with adhesion.)

  • Try a print with the above changes. If the problem still exists, and you aren’t having adhesion issues, move away from the bed a little (reduce negative Z-offset, either by entering a small positive 0.05-0.10 offset in Cura , or reducing the negative Z-offset in firmware by 0.05-0.10mm using the M851 command).

The nozzle is too close to the bed as mentioned earlier. Is it happening on all four sides, or just one side?

If all four sides, try adjust thing Z-offset by .1 or .2 through the LCD controls. If this helps, clean the nozzle thoroughly to remove any residue.

If only its not uniform, then you’ll need to troubleshoot your auto-level process. Watch the auto-level process and check if the nozzle is pressing down the print bed at any of the touch points. If this is happening, the print plane is being improperly defined. Most likely some sort of residue on the leveling discs… try cleaning the disc with acetone to dissolve any ABS residue.

I’ll give those tips a go. One thing I don’t have is issues with bed adhesion, in fact quite the reverse, so I will lower the bed temperature and also put the initial layer thickness back up.

Will get back to you with the results

Cheers

Les

Printing ABS, more adhesion is a good thing to prevent warping.

As you gain experience, you’ll be able to judge optimal initial nozzle height by looking at the bottom surface. The smoothness/roughness of the surface is as also a telltale sign of adhesion.

I like a pretty smooth bottom, but watch out for widening of the first layer. I also like a multi perimeter skirt, which I usually have to scrape off the PEI bed.

Last tip, pick a filament brand and stick with it. Dial in the extrusion temps and bed temp to get the most consistent results. I like eSUN ABS primarily because of price and I can get a 5kg roll. Print quality is good for the prototyping and my typical projects. My settings are initial extrusion and bed temps of 245 and 110 with no cooling from the print fan. At layer 10 (~3mm), drop the temps to 240 - 243 and 90 - 100 (still good adhesion, but allows bottom of ABS to cool rigid) with little to no cooling. For taller prints keep extrusion temps high 243-245 with no cooling to help adhesion of layered and prevent “splitting” as the project layers cool.

Hope that helps. Happy printing.