Defect in top layer in same spot every single time
Check these photos out. I'm printing a pair of pretty simple discs with tabs as pictured. I have printed dozens of these, and on every single set, on just one of my printers, I get this little blemish (right disc, in the upper right quadrant). I can't for the life of me figure out what is going on. It is always in the exact same spot. Anyone have any ideas? Printer is a MK3S+, This is PETG, .20mm layers, printed at 200% speed with the first layer set at 10mm/s (which translates to 20mm/sec at 200%).
RE: Defect in top layer in same spot every single time
That's varnish/dropping off of the nozzle IMO. How deep is the blemish - this happens from blobbing and burnt filament drops into the print. If it is happening every time, I am guessing you are using ironing instead of post processing (sanding) to get a smooth finish. Hard to believe that the burnt spot happens in the exact same place with the exact same shape every time ... but if you are getting a burnt spot there, you can try re-arranging the circles on the plate, and I'd suggest you get/make a good nozzle cleaner and do a thorough nozzle cleaning between prints.
RE: Defect in top layer in same spot every single time
Reseating the nozzle might help, it seems to be allowing a little seepage that you might not notice on some prints ... or switch to a dark filament which will not show the discoloration.
Cheerio,
RE: Defect in top layer in same spot every single time
I agree it's very odd that this same defect happens in the same spot every time, but it does.
It's kind of a lump there, which I'm guessing the nozzle then drags through and makes a little mess. No leaks anywhere. Nozzle and heatbreak/heatblock are clean, other than what accumulates on the nozzle tip during the actual print. I have a habit of using a brass wire brush on the heated nozzle before every few prints to clean the nozzle, and I definitely check it visually before every print.
So..... it's looking like an overextrusion issue. I set the flow from the default 95 down to 90 about half way through the print, and the top surface is clean now. I'll have to check my flow and extrusion calibration on this printer again.
RE: Defect in top layer in same spot every single time
@twoballscrewball
Try changing the orientation of the model, and of course clean the nozzle with a brass brush before each run.
Good Luck
Swiss_Cheese
The Filament Whisperer
RE: Defect in top layer in same spot every single time
OK another update here, I hate when folks don't update a thread with a fix so here's what I have so far.
Added an "M221 S90" in the gcode right after the first full top layer after infill. Results were better, but I still got some defects here and there.
When doing this, I noticed in the gcode that the top layer was .05mm. The second to top was 7.5mm. I remembered that I set this model to variable layer height in slicer, as I frequently do since it both saves print time while producing better results most of the time.
I sliced it again, again used VLH, but I manually increased the variable layer height on the top layers back to right around .20mm.
This has resulted in a few perfect prints in a row now. I think the .05mm layer height with a .40mm nozzle was just making a mess.
So far so good now. I print a ton of these parts so if I notice any more defects I will update, but for now I think the super low layer height on the top layers was the issue.
Thanks to all that responded!!!!!!!!!!