Sloppy top layer starting out of nowhere after good batches of same prints.

[ironliver316 0]

So I'm printing a ton of tank treads for a robot prop. I'm on a super tight budget and time frame. So I bought the cheapest grey PLA I could find on Amazon. Kingroon PLA at $14 for a kg roll. Needless to say, I wasn't expecting the best at that price, but the treads aren't really the focus, so as long as I could get them looking decent and functional, it's ok. So I can fit 5 treads on the plate at a time. I designed and sliced them to use as little material as possible and to lower the print time as much as I could with my very basic 3D printing knowledge.  I printed 6 batches, and they came out fine.

 

Then batch 7&8 came out like this.

 

So I thought maybe the nozzle was dirty from build up and snagging the PLA, so I cleaned it a bit and scraped of some gunk and batch 9 came out a little better, but still not the same.

 

I tried some trouble shooting online and seen it might be the temp, so I printed a temp tower, and all the bridging is equally sloppy.

 

Then I read about adjusting flow rate, so I set a tower to change flow rate from 80% to 120% and still crap.

 

I was watching one of the bad treads print, and I noticed even the infill wasn't printing evenly. Thick and thin spots like it was having trouble keeping a constant flow. But the first layer and brim are flawless. Perfectly even, no hiccups. If it was printing like this from the beginning, I'd just chalk it up to cheap filament. But to have it start after 6 good batches has me stumped.

[GregValiant 1,351]

I think the first thing I'd try would be to dry the PLA out.  45°C (115°F) for 4 or 5 hours.  If you don't have a low temp oven (one with a dehydrator is best cuz it'll have a fan) then you can just turn up the build plate to 45 and leave the roll on it overnight.  It will develop some brittleness but it may also print a lot better.