3 years of ownership ; I have not been able to cleanly remove a filament once.  

RE: 3 years of ownership ; I have not been able to cleanly remove a filament once.

RE: 3 years of ownership ; I have not been able to cleanly remove a filament once.

This has caused you enough aggravation over the years to invest in a new E3D V6 hot end.

Get the one without the Prusa MMU recess.

This does not address why you have heat creep in the first place (causes blob to form), but it should fix your unload problem.

RE: 3 years of ownership ; I have not been able to cleanly remove a filament once.

Posted by: @halle-s

I have not been able to cleanly remove a filament once. The filament always gets stuck below the bondtech gears because of a nozzle shaped blob at the end.

Just to be clear: You're unloading filament using the printer menu option with the filament heated up to printing temperatures when this happens, correct? A few thoughts:

• Since you're already heating the filament up to unload it, try extruding a bit before the unload action. Many people find this reduces the formation of the blob.
• If you're not at full print temp when unloading, or if it does get stuck, loosen the extruder tension screw(s) and see if it'll pop out the top. I do this when doing cold pulls. That should keep any blob from being trapped by the Bondtech gears.

I always get a small (~2.0-2.1mm) blob at the end of the unloaded filament that corresponds to the hotend meltzone dimensions. I've had this with my original (early 2018) and replacement E3D V6 Titanium heatbreaks. I'd be curious to see the dimension of your blobs. The "Prusa-fied" stepped heatbreak has a 2.2mm zone at the top, transitioning to 2.0mm lower down. I'd be surprised if a 0.2mm increase made such a difference, but it's worth checking into.

RE: 3 years of ownership ; I have not been able to cleanly remove a filament once.

@bobstro

Whether I do a pull at full temperature or do a cold pull by heating up to temperature and letting the extruder cool to 170°C, I cannot pull the filament out even when the idler door is opened all the way. The blob isn't terribly big, it's small enough that it doesn't get stuck in the PTFE tube, but it just won't get past the one bondtech idler without being cut.

I'm thinking it has to do with the filament path issue described here https://github.com/prusa3d/Original-Prusa-i3/issues/51 but then if that was the case, everyone would be having that issue.

RE: 3 years of ownership ; I have not been able to cleanly remove a filament once.

Posted by: @halle-s

[...] I'm thinking it has to do with the filament path issue described here https://github.com/prusa3d/Original-Prusa-i3/issues/51 but then if that was the case, everyone would be having that issue.

I'd also expect that to be an issue above the Bondtech gears, and I'm understanding that your blob is stuck below them.

Have you worked with your extruder tension screw(s) to ensure you're not over-tightening? I wouldn't expect it to matter with even semi-hot filament as you'd get during an unload, but it sounds like the space between your gears is really tight.

Is yours a Mk3 or Mk3s?

RE: 3 years of ownership ; I have not been able to cleanly remove a filament once.

@bobstro

It's an MK3. Which tension screws are you talking about? The only ones I know of are the ones on the idler door and they are irrelevant when the door is fully open.

The bondtech gear on the motor is what's blocking it.

RE: 3 years of ownership ; I have not been able to cleanly remove a filament once.

Can you snap and post a pic of the blob in place? If the open Bondtech is blocking it, that's something I've not encountered before. Typically it might require a bit of extra pull, but the filament is flexible enough that a blob will pop past the open gears. 

Have you tried extruding some filament before unloading?

RE: 3 years of ownership ; I have not been able to cleanly remove a filament once.

Posted by: @bobstro

 

Have you tried extruding some filament before unloading?

I want to thank you for this tip! That did the trick! Wow. I wish I had known about that 3 years ago!

RE: 3 years of ownership ; I have not been able to cleanly remove a filament once.

extruding some filament before unloading

This is why my firmware includes automatically extruding the filament a bit before removal. Makes for consistently clean filament ends.

RE: 3 years of ownership ; I have not been able to cleanly remove a filament once.

Posted by: @guy-k2

[...] This is why my firmware includes automatically extruding the filament a bit before removal. Makes for consistently clean filament ends.

Looks like there's a pull request to incorporate this into upcoming firmware. @guy-k2 is that yours?