Extruder Heater block (changing nozzles)
Just received my unit a couple weeks ago and I ran into an issue with the extruder thermistor open. Prusa is sending a replacement. While I had the extruder off the printer, I decided to remove the nozzle and replace it with a hardened steel nozzle which I just ordered from Prusa. The nozzle came off with difficulty (the assembly instructions said it was pre-tightened and I thought that was why it was so difficult) and upon removal found that the aluminum heater block had galled the threads on the nozzle and in the removal process the threads in the heater block are nearly completely stripped. Realizing that I also need a new heater block I attempted to unscrew the steel finned feeder tube assembly from the heater block. It too had the threads near the end galled and completer filled with aluminum and as a result the threads on the top side of the heater block are also mostly stripped. My question is what should I do to prevent this in the future. I do not relish replacing the heater block each time I wish to change the nozzle.
I did remove the nozzle when the unit was cold as the open thermistor prevented preheating the extruder. Does removing the nozzle when the extruder is hot eliminate the problem? Has anyone else has this problem with galling. The internet seems to imply that galling is common when mixing metals, especially aluminum. Replacing the nozzle with a new one is not a real issue, but digging the aluminum out of the steel assembly threads is a real pain. The aluminum has to be removed or the steel part replaced as the aluminum in the threads will prevent it from being used as is. I plan to head to the hardware store to find a steel nut that will displace the aluminum or cut it out by removing the starting threads on the nut.
A Google search suggest using a moly grease when assembling the part to prevent galling. Would MolyKote 41 from Dow Corning be a good choice to apply to the parts before assembly. It is good to 288C. Would teflon tape that is used in the plumbing industry ba a viable alternative if care was taken to assure no teflon in the filament feed path?
Peter, do you have any ideas on how I can prevent this issue in the future? I hate to have to nearly purchase a whole extruder assembly everytime I wish to change a nozzle.
Jim
Re: Extruder Heater block (changing nozzles)
Did a lot of reading on line tonight and found that the galling occurred during the assembly process for a number of reasons.
1. Threads not clean.
2. Units assembled too fast (use of power tools
3. Lubricant not used during assembly.
Since I experienced both the nozzle and feed tubed galled, I have to assume that the heater block was faulty in that the threads were not clean. There was nothing I could do in the removal that caused the galling. I happened during the assembly. I will contact customer support to see about a different extruder rather than just keep replacing it piece by piece.
Jim
Re: Extruder Heater block (changing nozzles)
Hi James
That's a new term for me "Galling". I presume that it means "Stripped"?
You should only ever release and tighten the hot end parts when hot. The expansion/contraction of the heater block will lock everything together when cold.
You also mention a steel tube. This part is only fitted to the V6 extruder (the Lite6 is all aluminium). The V6 has thermal paste between the steel heat break (barrel) and the aluminium cooling fins. Once heated (as this has been to insert the nozzle) the thermal paste will become more like a glue and again make disassembly very difficult, especially when cold.
The only time I have experienced the threads being stripped is with my Chinese clone, when I disassembled the extruder cold the threads in the heater block stripped. Occasionally I have forgotten to tighten the nozzle when hot and had to re-cut the threads (using proper tap/die set - well worth having).
I bought a spare extruder (V6) direct for E3D along with some extra spares (PTFE Tube, fan, thermistor wire insulation etc) as I am well aware that I will do something stupid at some point in the future to destroy the parts, because that's just what I do...
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Extruder Heater block (changing nozzles)
Peter,
Thanks for the reply. If you google the word "galling", you will see many references of problems when screws are inserted with power tools or the treads are not cleaned after the tapping process. It occurs most often when one of the metals is aluminum but can occur with other metals also. It is a form of "cold welding" that occurs between aluminum and the screw. The metals actually fuse together and in many cases the screw will twist off instead of stripping the threads. The fusing of the metals occurs as the screw is inserted in the aluminum, not as a result of heat applied later. Welding temperatures are orders of magnitude higher that what we are using in the extruder.
I was trying to get ahead of the game when my extruder was off the printer in pieces because of the thermistor failure. The system would not heat up and gave me an error message about "min heat" or something like that when I was going to preheat before a print. So I found the the thermistor open and after talking to Prusa, they are sending me a new thermistor and also a couple of nozzles that I ordered when talking with them via email. Since I plan to print some carbon filled material for building some drones I ordered the hardened steel nozzle. I though that I would remove the old nozzle while waiting so when the thermistor arrived I could replace the thermistor and nozzle at the same time.
The finned section on my extruder that screws into the top of the heat block is definitely stainless steel and not aluminum. The end two turns of the thread were completely filled with aluminum that was effectively welded to the screw. Nothing heat would have release. I heated the threads with a heat gun and attempted to pick it out of the threads but gave up and went to the hardware store and bought a tap and die set and ran the part through the die and re-cut the threads, thus removing the aluminum.
I noted that the nozzle should be tightened first all the way against the heater block. If the finned section is tightened first, the nozzle will hit the screw portion of the finned part before being completely tight to the heat block. I assume that the long threads on the nozzle are designed so that there is no gap in the heat block between the two pieces
Jim
Re: Extruder Heater block (changing nozzles)
Hi James
Thank you for your excellent definition. And indeed the fins are SS; I hadn't bothered checking previously, just assumed.
The nozzle should be fully screwed into the heater block and then released by half a turn. Then screw the fins onto the heater block, hand tight so that it seats against the nozzle. Finally heat the extruder and tighten the nozzle with spanners on the nozzle and heater block. If you don't do the last part, filament will find a way out! There will be a very small gap between the nozzle and the heater block.
It's not possible to use power tools to do any of this operation, so I don't understand how your extruder could get into such a mess.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Extruder Heater block (changing nozzles)
I had the same problem with galling threads. I emailed the company over two weeks ago asking about buying replacement parts but no one responded. Ended up buying the parts on Amazon.
I used a high temp anti-seize lubricant on the replacement brass nozzle. I swapped it out for a steel one today without any galling thread problems.