I could really use a hand getting rid of these black marks that appear randomly in my prints but are also common in areas of overhang. I am running out of time to print this birthday present.
Prusa i3, 0.4 jhead, abs at 220c
Where did you get the j-head? Looks to me like the filament is melting too high in the head and leaking out.
@Evan_Gillespie , it came with the i3 kit from makerfarm. I did recently disassemble the head and clean it out with a torch. The PEEK was a little darkened but didn’t look terrible.
If it is a cooling issue, any idea why overhangs would be more susceptible?
Could be there is a bit of plastic on the outside of the extrusion head. I had that problem it melted burned and dropped on my print.
@Matt_Harrington Nope. No other ideas.
Likely that this is some burnt filament on the outside of your nozzle is being left behind when it passes areas that have curled up to some degree. Try using Z lift on print moves and clean the outside of your nozzle. You may be able to reduce the curling by enabling supports. Also, it looks like you are over extruding to some degree, try dialing back your flow rate by 5%
Could not agree with Tim more. I run an i3, mine… not makerfarm. But, you are running heavy, not on parameters but top for sure. The print looks good, clean that nozzle exterior, reduce flow or increase speed on your solid fill. Whomever receives the gift will be happy I hope.
Looks like from your top solid fill pattern the nozzle is not perfectly vertical. My guess is you are pushing filament around with the nozzle as a result. That ends up on the nozzle and then gets deposited when you have part of the print curling up that rub the side of the nozzle. I have experienced this. It can also happed with buildup on the nozzle due to over extrusion.
You’re extruding way too much plastic. The flat/level areas should be level - the fact that there’s tons of plastic being pushed up above the level is a problem that’ll affect everything.
In addition to pushing out too much plastic, the molten plastic is probably backing up into the extruder, because only so much plastic can be pushed out the nozzle so the rest will just build up pressure in the extruder, which will cause it to sit in the hot end too long, which can cause burnt plastic, jamming, etc.
An easy way to fix this is to configure the ‘filament diameter’ to be larger, so the printer thinks that each step of the motor is pushing in more filament, so it pushes less in. It can be caused either by the filament being larger than the slicer thinks it is, or by the “steps per mm” for the extruder gear being wrong. But usually the “steps per mm” number is right, since it should be calibrated by the manufacturer based on the known gear radius, so I’d suspect that the filament diameter isn’t right.
Once you calibrate your printer properly, the print should look a lot better. If there’s any more burnt plastic after that, I’d suggest cleaning the nozzle. An easy way to do that is to get the nozzle hot, then press a chunk of scrap plastic onto the nozzle (e.g. a previous, failed print). Let the nozzle melt into the plastic a bit, then pull the plastic off. That should pull off any “junk” on the outsize of the nozzle. Repeat a few times if necessary.
If there’s anything after that, you’ll have to file it off. 
Re black marks … treat plastic and paint it …quick fix
I have cleaned the nozzle exterior with some acetone and alcohol. A set of comparison prints are running now with different extrusion multipliers. Dropping to 0.95 from 1 resulted in gaps between the lines. 0.975 looks similar to 1 at this point but it is hard to tell while it is still printing. This is a touchy setting. Is there another parameter I should be looking at?
slic3r 1.0.1, marlin 1.0.0
I think this is Greg’s Wade extruder
Photo of 0.95 (left) and 0.975 (right) extrusion multipliers: https://plus.google.com/photos/104268957202871548605/albums/6008704844565489393/6008705790851477794?pid=6008705790851477794&oid=104268957202871548605
If you notice there is a fat edge always to one side of the lines. I still recommend checking if the hotend is level.
I am having a hard time finding documentation on leveling the hotend. Should I do it based on the layer pattern or is there a more convenient measure I can use? I don’t think I could tell purely visually.
I have checked with feeler gauges against the glass, or a small square or square object along the hot end barrel (like a 3-2-1 block).
I just had a revelation: there may be a dark residue coming from the kapton tape. I noticed it when wiping down the nozzle with acetone and alcohol. Earlier while cleaning the nozzle with a torch, I also had to deal with some residue that appeared to come from the kapton.
Perhaps the kapton is leaving some gunk that migrates down the nozzle. This could explain some other things as well. Do people change their tape regularly? Maybe this is a bad roll?
There are no identifying marks, but it came with the makerfarm kit so I assume it is reputable. This appears to be it: http://www.makerfarm.com/index.php/6mm-kapton-tape-33-meters-long.html