Extremely Stringy Top and Bottom Layers!

[chuckdest]

Extremely Stringy Top and Bottom Layers!
After first getting the Makergear m2 a few weeks ago I leveled the bed with a dial indicator and performed various calibrations to achieve a nice cube shown here. I was off and printing various items. One night, I had a particularly large print that misprinted in the middle of the night. When I awoke I stopped the print. After this moment, I have not been able to get a decent print from the machine again. I have tried recalibrating, but something always goes wrong. The largest issue now seems to be that the top and bottom layers are printing extremely stringy. Infill and perimeter layers are printing perfectly. However, The top and bottom layers print much faster than the infill and perimeter. I'm getting pretty frustrated.
I am attaching an image of an identical calibration cube before and after the crash.

BadCube.JPG

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GoodCube.JPG

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[jimc]

ok by the looks of the skirt/brim around the print it looks like your bed gap is too tight. that looks really thin and transparent. if that first layer isnt right it will transfer up and could take 10-15 layers to correct. as for that top layer, that is a sign of running too high a temp but that also looks like the first layer over some fairly sparse infill. this can take 4 top layers to smooth out. drop your temp 10 deg, make that bed gap a touch bigger then run a test print and see if it gets better.

[Bratag]

It looks like there might be a leveling issue there as well. If you look at the brim it appears that one side is has all the lines merging where as the other has gaps.

[ednisley]

The top and bottom layers print much faster than the infill and perimeter.

It'd be worthwhile to check the slicer's speed settings for the top and bottom external surfaces, as they may have mysteriously changed while you weren't watching. Sometimes, at least around here, an errant mouse click or some blind typing will change a setting; there's no need to suspect foul play.

The bottom layer, in particular, should print very slowly to improve platform adhesion. That might be the root cause of a number of the other problems you're seeing.

When you get that sorted out, a thinwall calibration cube will help you get the Extrusion Multiplier reset to normal.

For PETG , I'm running 15 mm/s on the bottom and 25 mm/s on the top, with 75 mm/s for infill. Those speeds are glacial by the standards some of the hotshots around here use, but I'm in no hurry. You're probably running PLA, so those won't be directly applicable; the general idea, however, is to make it work correctly before you make it work faster.

[chuckdest]

Last night I cleaned out the hot end really well. Turned the temp down to 240 (abs), slowed the print speed to 1800 mm/min, increased the infill overlap to 40% Made sure everything was level and that the first layer was correct, and printed a zero infill cube to dial in a extrusion multiplier around .92. The bottom layer is beautiful again, and the top layer is acceptable based on the infill rate. Thanks for the help.

However when I try to print particularly large rafts, something goes wrong and the printer starts doing random movements. Extruding blobs in one place, backing the filament out of the extruder, and printing strange lines and skipping other lines.
As long as I don't use a raft, all is well.

Thanks,
Chuck

[jimc]

I have never used a raft in my life so i dont have much input. Do these movements show in the print preview?

[chuckdest]

No, They don't show in the print preview. Infact, lines that should be correct appear in the preview

[jimc]

only thing i can think of to test at the moment is to check to see if it does the same thing printing from sd card as it does usb. also when you installed s3d did you start with the default, correct makergear m2 process? this will configure the firmware settings. if those arent right or got changed somehow things can get wonky. might not hurt to reset all settings under help then reconfigure with the right makergear m2 profile. use the makergear profile in the drop down and remake your processes so everything is fresh. once remade toss your old ones.

[ednisley]

As long as I don't use a raft, all is well.

Well, as the saying goes: If it hurts when you do that thing, don't do that thing. [grin]

the printer starts doing random movements

Rafts slap down lots of plastic in a hurry to soak up platform misalignment, so it may be that the raft settings aren't correct (again, for whatever reason). Commands that call for extremely fast extrusion and very fast XY motion can require more torque than the steppers can produce, which usually causes what's called "missed steps", bad extrusion, and offset layers.

However, an overloaded stepper can stall, then begin turning backwards. That motion can continue through many G-Code commands, until a command eventually calls for a motion that lets the rotor snap into alignment again. Subsequent commands will work perfectly, as long as they don't call for more torque than the motor can produce, but (obviously) the object won't come out right.

Take a look at all the raft speed-and-feed settings to see if any look entirely unreasonable. I'd start with the values for ordinary (non-raft / non-support) printing, see if that improves the raft situation, then tweak from there.

[Rara]

As far as the stringing, is 40% overlap quite a lot? I run 10-15%, which I think is default in S3D; I wonder if the hot end is picking up material when it runs that far in to the outline.

I'd try reinstalling the software though..that is weird for a raft, I've never had any issues. Maybe a 1 or 0 is out of place somewhere..worth a shot.