So I’ve encountered a bit of a calibration conundrum. Originally I used to get a very nice first layer where each individual strand would overlap nicely with the adjacent one. But now I’ve noticed I don’t get that overlap anymore and the first layer has individual strands.
At first I thought this was just my M212 Z offset that needed recalibration. I tried that and it didn’t improve - and it didn’t seem safe to go any closer. Then, after closer inspection, it looked like it wasn’t just the first layer that was “stranded with no overlap” but it was subsequent layers as well. So I figured I was just under-extruding.
But now after setting my extrusion multiplier to 130%, I get artifacts in my full test prints - however my test prints of my first layer look perfect.
So here’s some pictures. In the square test print pictures, there are three prints:
- extrusion multiplier 110% - stranded result (strands can be separated by fingers)
- extrusion multiplier 120% - better, but still a little stranded
- extrusion multiplier 130% - perfect solid sheet for the first layer
And for the image of an actual model I printed, these are the results
- 130% extrusion - lots of over-extrusion artifacts
- 115% extrusion - still some artifacts
- 100% extrusion - looks just fine
So the problem is, it seems I need to extrude at 130% to get the first layer quality that I used to get (and additionally not always depend on using a raft), while meanwhile, my normal extrusion settings (100%) otherwise work well on a model and using 130% just isn’t acceptable.
Any ideas on what else I could do? Thanks!
EDIT: I’ve discovered another detail. It turns out that there is a pattern of “two bonded strands”, “gap”, “two bonded strands”, “gap” …
I have a close up image that shows this much better, but it appears I can’t add another image in an edit. Anyway, in the images here, what appears as a strand is actually two bonded strands! I don’t know what would cause that. This seems to be the underlying problem.
If you get two lines to a gap that’s you observing slop one of the horizontal axes. When you are under extruding it becomes more obvious.
Recently I had to tear down and rebuild my extruder because I had worn the hobbed bot down so badly. Recalibration then ensued.
Check for sloppy axes first or you’ll never be able to calibrate it out.
The problem is certainly first-layer setup related. Measure the thickness of a single layer and use that to compensate Z height.
I use a Mendel90 with Z endstop at the top. Setting the Z height involves doing this as a matter of routine. If the nozzle is set too high this is exactly the effect you see. Notice how the threads appear circular indicating the layer is not being constrained properly.
Subsequent layers are constrained in height by Z movement so they will print as expected but the first layer needs to be set right by you.
I hade the exact same problem with my core xy (the dubble strand/ gap problem). It turns out to be a bearing in a idler that had gone bad (the bearing was impossible to turn). This stretched the belt a bit when moving.
There’s three different things I’d consider here:
If this is the same material that you’d previously had used for good prints, has it gone “off”?
We had a roll that was about 12 months old that made it look like the printer was out. It was a little brittle and not feeding smoothly - mostly under feeding. New roll and everything was back to normal - checked and repeated the problem on a different printer.
If it’s a “new” roll, have you check the diameter, wouldn’t expect it to be varied enough to matter. On other hand, it could have been old stock - was it cheap / packaged without a descant pack?
Last one really relates to the fuse/no fuse - that sounds like back lash in one (or more) of the axis which could be the drive or loose fasteners.
Hope this helps.
Regards,
Colin
@Nathan_Walkner I can sort of see the point with uneven surfaces but not if it’s regular across the print - you’ll note the back lash on changes of direction and it’s going to be more consistent.
If it’s not level, you’ll see the problem more to one side than another.
Looking at the experience we had I’d say the fix appeared as @John_Hyland said “magic” with some fresh new material!
Yes, I don’t think it’s necessarily an uneven surface that is the problem since the issue is very uniform. And I have a feeling it’s not the filament that is the problem either - I keep it in a sealed container with desiccant. I’ve seen what happens with filament exposed to moisture, and I think this is not it.
I’m more inclined to think that the problem here is a slightly tilted axis/bed. Ooh, inclined 
I won’t have a ton of time during the week, but I’ll see what I can investigate soon. And in the meantime, I’ll carefully do some more tests with Z offset as well, but it seems slightly more strange that something like Z offset would go out of calibration. I feel like axes could skew more easily. But I’ll cover the bases.
Thanks for the feedback! I’ll update if I find anything.
I’ll still ask about age of filament @Perry_Parks some manufacturers state use within 6 months of opening… Alongside store in sealed air tight container with dessicant when not used.
Cool, non humid and UV also feature to varying degrees, also the care of storage can extend six months depending on use/storage conditions…
The filament we had trouble with was over 12 months old. As i noted, it seems like feed had gone out of adjustment but was instantly resolved with “fresh” filament… I wished we hadn’t wasted out time fighting with it 
@Colin_Durrans_minisu @Nathan_Walkner The filament is less than a year old - I’m not sure of the exact age. But yes, I’ve seen bubbling before, and this doesn’t ring of a filament problem to me from what I’ve seen before.
I’ve never seen bad filament and I never had a roll last longer than 3 weeks. What happens?
@Nathan_Walkner our filament was definitely more brittle but not to the point where it was obviously broken in the direct drive or bowden heads.
I don’t recall bubbling but it may not have been to saturated.
@Perry_Parks I’m expecting variation, that weather/moisture could lead to issues in less than 12 moths, even if you don’t see bubbling. Leveling will always helps, hope you’re sorted soon.
@Duncan_Gunn poor inconsistent prints.
@Nathan_Walkner @Colin_Durrans_minisu OK, I think it is not a warped platform, not a tilted z axis, etc. etc. Not due to old PLA.
It’s not a warped platform or anything like that because this happens on every layer - not just the first. If I look closely at subsequent layers on a 100% infill print, the pair, gap, pair, gap issue is there also.
After thinking though this, and doing a bit of research, I started to think that loose belt tension in one of the axes might explain this - it does appear to be just a problem in one axis perhaps (maybe Y).
Then I found this, which seems to agree:
http://support.3dverkstan.se/article/23-a-visual-ultimaker-troubleshooting-guide#circles
Note the orange picture of the paired strands. The description above it sounds exactly like my problem.
The downside of all of this is my Printrbot Metal Plus was assembled for me (they stopped selling kits) - so I don’t have the experience and knowledge of how to disassemble and inspect or tighten the belts. Very annoying, and exactly why I wanted a kit.
@Perry_Parks That was one of the suggestions I made
If I recall right, the printrbot z-axis is on a lead screw but it’s the x & y that’s on a belt. It’s the x & Y that appeared to be the problem in your picture.
Check screws are tight around the z lead screw mount - the mechanism has anti-back lash so unless it’s loose that should not be a problem.
Guides on the printrbot site should help you with setting tension in the X & Y axis belts - again I’m expecting you’ll find some thing that’s coming loose.
As for filament - it was printrbot where we first saw the trouble with old material. I’d expect to see miss-feeding around the “pressure roller” at the feed first.
I know there’s auto bed leveling on this printer, is it set correctly? There’s a commissioning check that might be helpful to repeat.
Good Luck!
