Heat Creep Blues

[GregValiant 1,358]

Ender 3 Pro.  Stock hot end, Orion BB hot end fan.  1.1.5 silent main board.  Aluminum extruder assembly.  In March the nozzle threads stripped out of the heat block.  Repaired with a heli-coil.  Filament is from Matter Hackers.

I've had it since December.  After the initial growing pains the machine has been printing perfect.  Now it has a new trick.

After printing for 35 - 60 minutes it stops extruding (with PLA at 210.  Using PETG at 245 it happens faster).  Doing a filament pull results in what you see in the image.  What you can't see is that from the extruder to the hot end, the filament looks like an accordion.  It is difficult to remove from the Bowden tube until it comes free with a slight pop.  There is a lot of friction from the accordion shape.  After pausing to clear the blockage and resuming the print, it happens again within 5 minutes.  Practically speaking -  the machine no longer prints.  This started 5 days ago.

Since the issue started I have:

Put heat sink grease on the inside tube of the hot end.

Added a thin aluminum plate to the backside of the heat sink.

The fan is clean and sounds like it is reaching operating rpm.

The hot end is assembled correctly.  There is no leakage.

The nozzles are clean.

The PTFE Bowden tube is new.

The tube fittings are new.

The extruder stepper motor runs cool.

Retractions do not slide the Bowden tube around.

Print speed has been varied from 60 down to 20mm/sec.  Retraction has been varied from 6mm down to 2mm.  Temperature for the PLA has been varied from 215 to 195.  Calibration has been double checked.  None of that has made a difference.

The extruder starts to skip steps on "prime" moves, and within 1 minute starts skipping constantly.  Spring tension appears good as witnessed by the accordion shape.  The filament appears to be getting shoved hard into the tube, but there is a blockage formed at the hot end of the bowden tube.

I have ordered a stock replacement hot end.  I do not have high hopes that it will cure the problem so I am looking for thoughts and ideas.

 

June 30 and the new hot end is in and it's better, but still not right with either PLA or PETG.

 

 

 

Edited July 1, 2020 by GregValiant
More Info

[GregValiant 1,358]

Well, there have been no suggestions so I ordered a replacement hot end fan.  My current theory (theory #41a) is that some strings have wound around the shaft of the fan rotor and it isn't putting out what it should.  I arrived at this theory because everything besides the fan has already been replaced.  I ordered a Delta 4015 and will put a 1/8" spacer behind the metal cover to move it outboard 3.2mm.  That should allow the 12cfm fan to fit inside.  Theory #41b states that Creality put all the cheapest stuff they could get away with in the machine along with cutting the physical requirements as close as they could.  I figure you can't over-cool the hot end.  If 80% more air doesn't cure the problem I'm gonna design a dry ice system.

[GregValiant 1,358]

Fixed.

It was me all along.  I would leave a bit of Bowden tube sticking out of the inner heat sink tube so that when I installed the nozzle it would assure a seal.  Turns out a little is a lot and the bottom of the tube was distorting and getting too narrow.  So I threw out my not-so-great idea and all is good.  I think I'll go sit in a corner now with the pointy dunce hat on.

I do have the coolest hot end in town though.