[Solved] Nozzle changing issue  

RE: Nozzle changing issue

And what nozzle do you use? Long or an extension and a short nozzle, because it is not clear from your question, because E3d produces both types. They really differ in assembly: Screw the extension into the thermal block from above until it stops and then screw the short nozzle to it while it is hot so that the mentioned gap remains between the block and the hexagon, otherwise the filament will flow out around the thread. Long nozzles are screwed into the thermal block until it stops and tightened a little. And I would personally switch to long nozzles, because there are no such worries with them and they are easily replaced when cold.

RE: Nozzle changing issue

I am using a long hf replacement nozzle: https://www.prusa3d.com/product/e3d-prusa-nozzle-high-flow-obxidian-0-4-mm/

Thanks for the clarification: "Long nozzles are screwed into the thermal block until it stops and tightened a little. "

RE:

while the general hotend instructions say to keep 0.5 mm between the tip and the heat block

Where did you get that from? All the core one nozzles (or Mk4) get screwed in completely. The only exception would be if you used the nozzle adaptor to attach a traditional E3D V6 nozzle (which Miroslav referred to as "extension and short nozzle"). But you didn't mention any of that.

Maybe show us a picture of the nozzles you're working with or links to where you ordered them from. Also, when you switched to HF, did you also switch the printer profiles to HF? If not, that would explain your problems.

RE: Nozzle changing issue

https://help.prusa3d.com/article/extruder-noises_2013

when you scroll down to "hotend assembly". in the meantime i realized that this info is only valid for the "extension and short nozzle" like both of you mentioned.

I set the printhead in the hardware menu to hardened, but I did not change the printer profiles in the prusa slicer yet, as I cannot laod the filament in the first place.

RE: Nozzle changing issue

I eventually solved it. I released the thumb screws a lot more then in the previous attempts before inserting the new nozzle and also looked at the instructions for the nozzle replacement tool once more, paying specific attention to this step: "1. The gap on the front of the tool is intended to go into the front horizontal bar of the printer, to give the tool more stability." I also shaped the filament tip very very sharply before loading it again. 

RE: Nozzle changing issue

I had the exact same issue when installing the ObXidian HF nozzle in my Core One.

Turns out, E3D nozzles (like ObXidian HF) have different proportions compared to the Prusa nozzle shipped with the printer.

I made a new nozzle replacement tool which takes this into account. In the description I also explained the reasons and differences compared to the stock nozzle in detail:

https://www.printables.com/model/1260118-core-one-nozzle-replacement-tool-for-e3d-nozzles

Try printing & installing this new tool for your ObXidian HF. If it does not fit, your heater block is too low. To fix this, unscrew both thumb screws while holding the heater block (make sure the printer cooled down first!). Then gently push the heater block up, now tighten the thumb screws again. Now you can check if the new custom nozzle replacement tool fits on your hotend, otherwise your heater block is still to low.

Let me know if that helps!