I'm not having any problems with the filament coming off the spool.  I actually modified my spool holder to keep the top of the spool above the printer, that way, there's no possible rubbing or binding against the frame itself.

As for leveling the bed, I just did that the other day, I had to make my own holder, as the one from Thingyverse didn't fit right, but I got the job done.

At the moment, I'm not having this problem.  What seems to have fixed it was to tighten the pressure plate screw.

Awesome to hear I hope that it keeps on printing for you, I know the frustration that comes out of not having things print when it comes to the filament not working the way it should.

5) (THIS IS A BIG ONE THAT IS OVER LOOKED A LOT) Your spool is not on a spindle of some sort to help it so it dose not have drag on it as it prints, this causes the filament to not be able to be pulled in with the hob bolt as it is fed into the printer. 

6)  ( This one kind of goes with 5 ) your filament is twisting as it is pulled into the printer and this causes tension on the filament in the spool causing it to not freely be pulled into the printer.

I'm not having any problems with the filament coming off the spool.  I actually modified my spool holder to keep the top of the spool above the printer, that way, there's no possible rubbing or binding against the frame itself.

As for leveling the bed, I just did that the other day, I had to make my own holder, as the one from Thingyverse didn't fit right, but I got the job done.

At the moment, I'm not having this problem.  What seems to have fixed it was to tighten the pressure plate screw.

The Good
#1 You can see gripping that is evenly spaced and even depth into the filament this is a " good " tension setting this is what you want to see when you pull it out  when changing colors.

The Bad
#2 This tends to happen for a number of reason I have found, its bad but fixable, this is mostly caused buy the spool catching and not pulling into the printer freely, and can be caused by the filament being twisted as it is pulled in. In some cases I have found that it is due to the pressure on the hob even
This can lead to the filament being so chewed in one spot that it becomes Ugly

The Ugly
#3 I call this the ugly because this is where you by the sounds of it where during your print, hit a print point where the hob chewed threw it and made a pile of little shavings/crumbs below yet wouldn't feed any farther beyond that point. tends t break if you look at it wrong when removing even because it is so thin, and if your tension is to much on the plate I have seen it at times eat all the way threw....( oh what fun that was to fix )

1) Not all ABS and PLA print at the same temps. I have found that some print at 220C while others print better at 230 and 215 for the ABS and some of the PLAs print at 175 perfect while others where better in the 180 range.

2) My print bed was not as level as it should have been causing the printer to back up in spots and not extrude as much plastic in that spot as in others. This caused a sort of clog as it printed because it was pushing to much "water" threw the opening for the space to allow.

3) My feed was faster then my print rate ( I was tinkering some with how things printed and forgot to set this part up at times )

4) To much tension on the filament seemed some times to be a bad thing BUT never caused the hob chew to an extreme unless it was way to tight.

5) (THIS IS A BIG ONE THAT IS OVER LOOKED A LOT) Your spool is not on a spindle of some sort to help it so it dose not have drag on it as it prints, this causes the filament to not be able to be pulled in with the hob bolt as it is fed into the printer. 

6)  ( This one kind of goes with 5 ) your filament is twisting as it is pulled into the printer and this causes tension on the filament in the spool causing it to not freely be pulled into the printer.

How To Fix And Prevent

1) Test print new filaments on a small print and see the ideal melting temp before you do large prints.

2) If you do not have one already get your self a drop dial/ dial gauge and print off a dial gauge holder for your X axis to level your print bed with. ( can be found on Thingiverse if one is in need and can print one)

3) Find a feed rate that works for that print speed ( takes time but some times is worth it )

4) Loosen/ Tighten the tension some and see if that helps

5 and 6) Make a spool holder that holds your spool so that is can pull in the filament freely with little effort. ( some times you can find them on Ebay for under $30 USD with shipping included, that are really cool that work wonders on most spool sizes and printer types.)

Hope this helps you or even some one else that is going threw this situation, I hated when my hob decided it was hungry and chewed up my filament in the middle of a print, caused me to lose a lot of filament that was unusable  after.

( I will try to post so pictures soon with this of good and bad )

Maybe, make sure the plug for the extruder motor is firmly plugged into the electronics board. I've actually seen my motor vibrate but not quite turn, even when the plug looks like its in. Pushing it in firmly has solved this problem.

The fan is not the problem, it's working fine.  I tightened up the pressure plate screw and it seems to work a lot better now.

My extruder heat-sink fan has been flakey from day 1 and usually needs a little nudge to get started.  If I forget to do this, heat eventually works its way to the parts that grip and move the filament.  This softens the plastic enough that it starts slipping.  If I cancel that print and get the extruder fan going again, the slipping stops.  Might not be your problem but worth checking.  Cheers.

PS A good indication of this would be that it grips the filament well at the beginning and starts to slip more and more as it heats up.  If you have slipping when you first start the printer it's likely not caused by this.

I don't know, I haven't really looked at it.  I know that in the beginning I noticed that the extruder back fan was nearly always on, but haven't paid attention to it lately.  I'll take a look tonight when I go back to see if it turns on automatically and stays on during the job.

Is the toothed gear in alignment with the peek opening?  Are you using the MK4 or jigsaw or something different?

It looks aligned when I look down thorugh the feed hole on top of the extruder, but I don't know if there is any side to side play inside (along the shaft holding the gear).  I doubt it though as I think the gear is secured on the motor shaft with a set screw, it's not on a splined shaft.

As for the MK4 or Jigsaw, I don't know what those are.

Could this problem be due to size/diameter inconsitency in the filament ?  As in it gets to a spot where the diameter is smaller than usual, doesn't get a proper grip and it starts to slip and eventually errode the spot ?

PS A good indication of this would be that it grips the filament well at the beginning and starts to slip more and more as it heats up.  If you have slipping when you first start the printer it's likely not caused by this.

What happened is that the filament got chewed up in one spot by the feed gear and then failed to feed any further.  This is perhaps the 3rd time tis happened.  I tried adjusting the tension using the pressure plate screw on the side of the extruder, but I'm not sure if this is the problem or not.

It doesn't do it consistently enough to point to anything in particular.  Originally I thought this might have been caused by the filament binding on the spool, but I don't think that's it.  I have previously modified the spool holder so that's actually sitting above the printer and makes it easier for the head to pull the filament.  After this morning's failure, I checked to see if the filament was bound up, but it's not.

So what cause this, or is this something unusual?  AM I adjusting the pressure improperly (too much, too little)?