I’ve had my A8 for a couple of months now, and it’s been working great. I was really happy with it and the quality of prints it produces.
Until 2 weeks ago that is. I bought some PETG to try out, and the print went spectacularly wrong. It seems that after a few layers the filament stopped adhering and just spewed out everywhere. During this the heating element came out the head and got utterly covered in burnt filament (I guess it got ramped all the way up because there was no way to register the temperature), along with the hot end. Somehow the nozzle also ended up *below* the bed height, so the bed tape got scorched and the bed heater plug has a few melt marks on it.
I have since purchased a new heater, and cleaned up the hot end. But I have yet to produce a decent print again, even with PLA which had been working wonders before. What usually happens is that it prints a few layers, then filament stops extruding. But it’s also randomly moving either the X or Y to an extreme (not always in the direction of the limiter, so hits the end and slips), and so I’m getting layers offset by a few mm. All in all, I’ve gone from about 80%+ print success, to under 10% (I did print one 20mm calibration cube OK).
Any idea what’s happened? I’m wondering if I’ve fried the board with it trying to heat the nozzle but the thermistor saying it’s cold. No mosfet fitted yet (on order), so quite probably I reckon.
Extra info:
I use Cura 2.5 for my slicer. I control the A8 using OctoPi. Successful prints were in PLA @ 210c head, 60c bed. Not now though.
Offset layers are usually a sign that the belts are slipping. Or the toothed gear isn’t tightened.
The belts are properly tensioned, and the gears are secure. Like I said the printer randomly just goes to the limit of X or Y for no reason. If it goes in the direction that doesn’t have the end stop switch then it just jumps the belt a couple teeth until it decides to go back to the nearly right place. The offset layers is a symptom of that odd behaviour not a loose fitting.
Recheck your slicer settings and make sure you have your printer dimensions accurately dialed in, too. Something might have changed when you switched to PETG and redid those settings.
As best I can tell my settings are appropriate. The bed size is correct, temperature, filament size, speed are all as I have been using. I’ve been printing small items, under 50mm x 50mm in the bed centre, so there is no earthly reason why the printer would need to move to an extreme end of it’s travel. I’ve even run the GCode through gcode.ws and it doesn’t show any attempt to move to the ends of the axis.
But this also doesn’t answer the big problem, why it extrudes just fine for the first few layers, then just stop completely.
What sort of gap should I have between the top threaded tube and the bottom of the filament feed wheel? Also, which way up should the tube go? Should the end that the plastic insert enters be at the top or bottom? I bought these to replace the original https://www.amazon.co.uk/gp/product/B06W5C9CGS/ref=oh\_aui\_detailpage\_o02\_s00?ie=UTF8&psc=1 and I didn’t note which way round the original went.
The PTFE insert should be visible at the bottom of the threaded tube so it makes a seal with the nozzle.
Are the first few layers really tight on the bed? Do you here a clicking sound as the filament slips through the extruder gear as it struggles to extrude?
What temperature were you printing at too? I’ve seen a head clog up before, but only because it couldn’t get the filament out and it kinda burnt inside the nozzle.
OK, so I have the threaded tube the right way round, that’s good.
I generally set the bed so that a piece of paper is well pinched between the bed and nozzle. I’ve also tried making it a bit looser such that a piece of paper has a slight bit of drag. The first few layers go down fine either way. I don’t think there is any clicking from the filament slipping, but it does seem to develop a slight kink and stop feeding. What should the gap between the top of the threaded tube and bottom of the feed gear be?
I had been printing this PLA at a fairly high 210c with great results. I’ve tried lowering it down to about 195c but still fails.
OK, that’s good.
I’m scratching my head on this one, but have a few more things to think about.
Is the extruder still going when the printing stops?
Does the temperature of the hotend drop at all during a print? If it drops too low, extruding will stop.
Have you still got the random movement of the X and Y axis?
Well, at least I’m not the only one scratching my head. 
Because of the stupid design of the cooling fan I’m unsure if it’s still trying to extrude or not. According to the readout in Octoprint the temperature of the hot end stays within a few degrees of the set temperature, so it should be fine.
I haven’t tried a print in a few days as there doesn’t seem much point until I have changed something. I might try another small print this evening without the fan attached so I can watch the feed system.
I’m still wondering if something on the mainboard got damaged when the print failed. I’m wondering if maybe reflashing the firmware might help. I’ve been wanting to change over to Skynet so I can try out auto-levelling. Maybe this is as good a time as any to do that.
Thanks for your help so far all.
One thing I would ask. Have you tried printing using the SD card? But, I think you are probably right in suspecting the board being damaged.
Yes, I’ve tried directly from the SD.
Weirdest thing, without making any real ‘fixes’ it’s been printing all day pretty much perfectly. I’m just having to redo one print, but that was my mistake not the printers.
