I'm starting to become painfully aware of how different various PLA filaments can be, even from the same seller.
And no, it's not just the temperature, as most posts would lead you to believe.
I've been using Faberdashery's electric blue PLA (
http://www.faberdashery.co.uk/products- ... tric-blue/) yesterday and couldn't, for the life of me, get it to print nicely. The layers are horribly uneven. Okay, maybe not horribly, but very very noticeably, especially at oblique lighting angles. Faberdashery's black, on the other hand, prints awesome and very even, especially if you lower the temps a bit (counter intuitively - most tips i've heard suggest increasing the temperature to get more even flow).
Now, at first, i thought it's a simple matter of lighting and texture. But putting a few test prints side by side, it gets obvious that the more noticeable unevenness is not an artifact of lighting (sorry, don't have a photo right now). Then i thought, maybe it's temperature, and played around a bit. And nope - same deal, regardless of temperature (tried everything from 180C all the way up to 210C).
And then i've noticed something... Faberdashery's black, as well as Ultimachine silver and some other filaments that i've found print really nice and even, all have one common characteristic - they don't break easily. As in, if you make a free air extrusion and bend it, you can bend it nearly 180 degrees 5-6 times before it breaks. In fact, some, like Ultimachine silver, i have to cut with scissors when there's a strand of extrusion left hanging cold from the nozzle. I can bend them and twist them to no end and they simply don't snap or break.
Faberdashery electric blue, on the other hand, as well as Ultimachine white and black, break easily, with a loud SNAP sound. And all of these tend to print unevenly.
I've been thinking what the cause of that correlation might be and so far, my working theory is that the brittle filaments get mangled much more by the hobbed bolt, as they're less elastic (and less plastic). Instead of the teeth digging into the filament and deforming it, chunks of filament break off, clogging the bolt teeth and slipping of the filament during retraction and post-retract extrusion. Sure enough, after using the electric blue for a few hours, i've removed the idler block and the bolt really was pretty clogged up with it.