Nozzle torque: 1.5Nm, 2Nm, 3Nm?
Short version: When replacing the nozzle, how tight should it be? On the Prusa site, I can find a both written and video instructions. One says 1.5Nm but the other says 2.0Nm. And the E3D V6 instructions for the kit version of the hotend say 3.0Nm.
Long version:
After many happy years of printing with my pre-assembled MKS3+, I started having problems with PETG clinging to the nozzle and creating blobs. I cleaned up the heater block and the nozzle. Cold pulls would come out perfectly shaped yet the problem would recur with 100% certainty with PETG. I switched back to PLA, which would usually succeed, but the PLA prints were marked by occasional drops of the previous PETG color that, at the time, I was unable to explain.
Somebody suggested that even though my nozzle is clean, the opening may be worn from use and that could cause the extruded plastic to come out at an angle, increasing the chances of it sticking to the surface of the nozzle. Nozzles are relatively inexpensive, so it seemed worth swapping it just to see if that would resolve the problem. So I embarked on my first-ever nozzle replacement.
I removed the old nozzle and discovered that its threads were entirely coated with PETG. Interesting.
Per the Prusa instructions, the new nozzle is supposed to be screwed in (1) until it cinches up against the head break inside the heater block, (2) is about 0.5 away from hitting the heater block, and (3) be tightened to either 1.5Nm or 2Nm of torque. There was simply no way to meet all of those requirements. I tried fitting the old nozzle back in, and concluded that it had only seemed tight because of the PETG coating its threads.
Somebody suggested that the heater block wasn't screwed far enough up onto the heat break. (Since day 1 on an factory assembled printer?!) It would explain the problem I was having trying to fit the new nozzle into place and why the old nozzle's threads were coated in plastic.
I removed the hotend in order to try to screw the heater block up. I'm unable to screw or unscrew the heater block from the heat break. I cannot unscrew the heat sink either. In the gap between them, there's a column of PETG hold the three parts together. It appears that, not only was there a leak inside the heater block, but also inside the heat sink.
So I ordered a new E3D V6 hotend from Printed Solid (the Prusa-authorized re-seller in the U.S.). I got the kit version, so I searched for assembly instructions. E3D has an excellent video explaining the process, but it says the nozzle torque should be 3Nm.
While I'm waiting for my PTFE order (because I mangled the original piece removing it from the old hotend), I thought I'd ask about the torque.
Best Answer by Diem:
Somebody suggested that even though my nozzle is clean, the opening may be worn from use
It's not the opening that usually wears, it's the tip - like a pencil slowly becomes blunter so does a nozzle - that's why your first layer 'Z' offset calibration drifts with use and must be recalibrated from time to time. Compare the two under a magnifying glass. With a typical heavy-hobbyist duty cycle of abut 40% you can expect 6 - 9 months life from a brass nozzle before the flat area outside the opening grows too wide.
Be aware that there are nozzles available from China that are a fraction short in the thread and will not fit, sometimes these are sold as E3D parts by unscrupulous traders; genuine E3D nozzles from Prusa or E3D themselves, will.
I'm unable to screw or unscrew the heater block from the heat break. I cannot unscrew the heat sink either. In the gap between them, there's a column of PETG hold the three parts together. It appears that, not only was there a leak inside the heater block, but also inside the heat sink.
This does read like a wrongly inserted nozzle but if this was from the factory you would have been complaining about severe blobbing years ago...?
The failure to unscrew is odd - you are working with a heated part as per Prusa's instructions?
As I understand it Prusa's suggested torque is fine on a new part with clean threads but E3D's is better for replacing worn/dirty parts. It's not too critical, shoot somewhere in between.
Cheerio,
Somebody suggested that even though my nozzle is clean, the opening may be worn from use
It's not the opening that usually wears, it's the tip - like a pencil slowly becomes blunter so does a nozzle - that's why your first layer 'Z' offset calibration drifts with use and must be recalibrated from time to time. Compare the two under a magnifying glass. With a typical heavy-hobbyist duty cycle of abut 40% you can expect 6 - 9 months life from a brass nozzle before the flat area outside the opening grows too wide.
Be aware that there are nozzles available from China that are a fraction short in the thread and will not fit, sometimes these are sold as E3D parts by unscrupulous traders; genuine E3D nozzles from Prusa or E3D themselves, will.
I'm unable to screw or unscrew the heater block from the heat break. I cannot unscrew the heat sink either. In the gap between them, there's a column of PETG hold the three parts together. It appears that, not only was there a leak inside the heater block, but also inside the heat sink.
This does read like a wrongly inserted nozzle but if this was from the factory you would have been complaining about severe blobbing years ago...?
The failure to unscrew is odd - you are working with a heated part as per Prusa's instructions?
As I understand it Prusa's suggested torque is fine on a new part with clean threads but E3D's is better for replacing worn/dirty parts. It's not too critical, shoot somewhere in between.
Cheerio,
RE: Nozzle torque: 1.5Nm, 2Nm, 3Nm?
It's not the opening that usually wears, it's the tip - like a pencil slowly becomes blunter so does a nozzle - that's why your first layer 'Z' offset calibration drifts with use and must be recalibrated from time to time. Compare the two under a magnifying glass.
Yes, under magnification, I can see the old nozzle has a wide flat area. I did periodically recalibrate Z when doing routine maintenance, but the offset I ended up with for any particular build plate never changed by much.
This does read like a wrongly inserted nozzle but if this was from the factory you would have been complaining about severe blobbing years ago...?
You would think. I suppose I did very occasionally have a dot of a previous color end up in a print, but blobbing only recently became a problem. My guess is the leak was very, very slow, especially once enough plastic accumulated inside.
Be aware that there are nozzles available from China that are a fraction short in the thread and will not fit
Thanks for the warning. I am aware and have checked them all carefully.
The failure to unscrew [the heater block and heatsink from the heat break] is odd - you are working with a heated part as per Prusa's instructions?
Getting a firm grip on the round and slippery heat sink while the extruder is only partially disassembled proved challenging. I could have tried a heavier wrench, but I feared damaging the fins (or slipping and damaging the thermistor and heater wires).
Once I'd committed to replacing the entire hotend, I removed it from the printer. To my surprise, the outer insulation on the heater cartridge wires is badly damaged in several places where it had been wrapped in the textile sleeve (not at any of the points that were clamped or zip-tied), so I was uncomfortable using the cartridge to heat it again. So I clamped the heat sink into a heavy vise, heated the assembly with a heat gun and took a wrench to the heater block. It took some effort and it did some damage to the heat sink, but I got the heater block unscrewed. When I then tried to unscrew the heat break from the heat sink, and the heat sink sheared off as soon as I applied any pressure.
As I understand it Prusa's suggested torque is fine on a new part with clean threads but E3D's is better for replacing worn/dirty parts. It's not too critical, shoot somewhere in between.
Thanks, that's what I needed to know.
RE: Nozzle torque: 1.5Nm, 2Nm, 3Nm?
I’d say that 3 Nm is a very high torque for a brass nozzle and aluminum heater block. The chances of snapping off the bottom from the threaded part aren’t negligible, specially with cheapo clonic models. Even with original E3D nozzles, I wouldm’t go higher than 1.5 Nm.
Hardened steel units are tougher of course, but then you risk damaging the heater block or the heatbreak if you “overtorque” the nozzle