WTF is wrong with my extruder??  

RE: WTF is wrong with my extruder??

Reading some other posts about extruder issues, some seem to lean toward extruder motor problems, but during the most recent extruder/hot-end tear-down/cleaning/adjusting (there have been several), turning the extruder motor by hand seemed absolutely normal, no binding, step backforce normal and consistent. If the motor was skipping steps, I would expect to see a gradient on the extrusion, but the hard edge on the stripes and consistent dimensions seem to mitigate against random step skips. A loose wire would likewise not explain such a consistency as far as my mechanical analysis takes me. Not at the machine as I write this so will have to post the F/W version later, but issues with that too seems to me to be a long shot.

RE: WTF is wrong with my extruder??

Possible important detail: with elevated Z axis, heated nozzle, moving E axis with control knob yields VERY inconsistent results. Descending "stream" is not consistent in width or speed and stops altogether after about 10 seconds, no matter how many "steps" I dial in. This is through a wide range of idler spring tensions from very light to very heavy.

RE: WTF is wrong with my extruder??

Possible important detail: with elevated Z axis, heated nozzle, moving E axis with control knob yields VERY inconsistent results. Descending "stream" is not consistent in width or speed and stops altogether after about 10 seconds, no matter how many "steps" I dial in. This is through a wide range of idler spring tensions from very light to very heavy.

RE: WTF is wrong with my extruder??

Starting to think upgrading to MK4S might be easier that trying to fix this. Thoughts?

RE: WTF is wrong with my extruder??

Lest there be any confusion, I am NOT attempting to print a "bar" pattern. The model is a 260mm x 30mm x 0.3mm continuous sheet.

Have you checked the extruder idler bearings?

Cheerio,

RE: WTF is wrong with my extruder??

Not sure if these "bearings" are the ones you are referencing, but if they are, there is absolutely no binding and no "slop" in the fit. The problem appeared basically overnight, it was fine one day and broken the next.

RE: WTF is wrong with my extruder??

There is also no slop or binding between the idler frame and its pivot screw.

RE: WTF is wrong with my extruder??

On the MK3S, you have the window on the right side, extruder idler housing, which you can seee the hob gear, you also have the exposed shift on the front of the extruder motor visible. Have you watched each of these to see what is happening or no happending when it stops extruding after 10 seconds?

RE: WTF is wrong with my extruder??

exposed shaft on the front, can't edit to fix or my other typos, as Prusa continues to let this forum die after, numerous empty promises. 

Yes, the bearings inside the Bondtech gear -

Second picture on: https://help.prusa3d.com/guide/5-e-axis-assembly_169235#169636

 - do they turn freely?

And your Bondtech gear teeth appear somewhat chewed ... if the teeth on the drive side are as bad it may be time for replacements.

Cheerio,

RE: WTF is wrong with my extruder??

Good question, I'll check and report back. (Agree with your short edit window comment.)

RE: WTF is wrong with my extruder??

Ok, so I did another cold pull (nominal) and disassembled the extruder for cleaning. When I reassembled it, I had a Eureka moment! What if I was over-tightening the pivot screw for the idler door? This would pull the extruder frame inward, constraining the door and not allowing it to pivot freely. So, put very little torque on the screw and tested for free movement. Nominal. Cleaned the bed (again, thoroughly), heated the nozzle to 220° C (for PLA) and started manual movement of the extruder (E axis). Got a MUCH more consistent stream out of the nozzle (diameter-wise), but it would come out at differing angles and directions. At random intervals, it would slow down, forming small blobs before speeding up again. (Photo.) This seemed, at least, some progress. So I decided to do a First Layer cal. Except for a small under extrusion at the start (upper-left, photo), everything looked nominal, UNTIL it got to the final square at the lower-left, whereupon, like a switch being thrown,the bottom half of the square is almost entirely missing. Now what?

RE: WTF is wrong with my extruder??

Other photo

RE: WTF is wrong with my extruder??

Not your main issue but your first layer offset calibration may be a fraction low ...

also see:      https://help.prusa3d.com/article/bed-level-correction_2267

Did you follow @ruebarb's suggestion to watch the gears when extrusion is failing?  What did you see?

Got a MUCH more consistent stream out of the nozzle (diameter-wise), but it would come out at differing angles and directions.

This is often a symptom of a worn nozzle.

Cheerio,

RE: WTF is wrong with my extruder??

Watching the bondtech gears through the idler door "window", I am now getting a continuous (does not stop after 10 seconds) although spacially erratic stream, i.e., the diameter is consistent but the "spaghetti ball" is very diffused with random "blobs", as in the picture. I attribute this "improvement" to the lessened torque on the idler door pivot screw. But the stream ( 0.4mm nozzle) does not form a nice uniform spiral like it does with my Mini. As far as the nozzle being worn, it IS the original nozzle, but I  am not near the machine at the moment so I  can't  give you the total running time. Will report on this later. Pretty sure  it has less than two hours running anything CF'd. Also, this seems a low probability to me since it was fine one day and misbehaving the next.

I usually expect to change brass nozzles around 6 - 9 months of printing at 40% duty cycle with average filaments - luckily nozzles are one of the cheaper spares.

Nozzle damage, eg chipping, can happen overnight.  White and pastel filaments wear nozzles about twice as fast as black or clear...

Waiting for the gear report.

Cheerio,

RE: WTF is wrong with my extruder??

FYI, the total filament thruput has been 14.5K meters with no more than 200 meters (if that) of anything abrasive. 

Still wondering how a worn nozzle explains the maddening "hard edged", regular transitions from extruding to not-extruding shown in the first pic I posted?

I did post above my observations regarding the gears operating. What other detail or clarification do you need?

The variation still looks like an issue with the Bondtech gears - either drive or idler, perhaps both - as if the contact/grip pressure is varying. That's why I suggested you check the bearings, if one has collapsed the gear will be eccentric and pressure will vary periodically with the rotation.

If the bearings are sound then you might be best to contact Prusa Support via chat as I'm out  of ideas.

thruput has been 14.5K meters with no more than 200 meters (if that) of anything abrasive.

All filament is abrasive to some degree, some far more than others.

Cheerio,