Hotend Thermistor Replacement Trouble
The real problem here is the screw for the Thermistor, but I wanted to briefly mention my confusion at the sets of instructions available.
A little while ago, after having no trouble, it started recording the ambient temperature at 7-10 degrees celsius lower than the print bed thermistor. I was reluctant to fiddle with it, so I printed one of those temperature towers that was recommended to me (I think by someone here, thank you, it helped a lot!) and I was able to keep printing.
The ambient temperature now dropped a few degrees due to Autumn, and unless I heat my room like crazy, I get mintemp errors.
I found two sets of instructions:
https://help.prusa3d.com/en/guide/how-to-replace-a-thermistor-in-the-extruder-mk2s_22208/ - the top of the page says it's relevant for MK3, but I don't think it should say that, as the back of the piece where the hotend sits is not the same at all. It looks open on the MK2 and more closed on the MK3.
https://help.prusa3d.com/en/guide/how-to-replace-a-thermistor-in-the-extruder-mk3s_131675 - this only lists the MK3S, which I do not have, but it is so much closer to what my printer looks like that I have been following it.
The problem I am having, after following the latter set of instructions, is that the screw for the thermistor will not turn. I have tried every allen key that came with my printer, from the smallest until it became painfully clear that it was too big when it started stripping metal from the sides of the hole for the screw.
The screw won't turn, and I cannot get the thermistor out to replace it. What can I do? I am at my wit's end trying to find a way to replace the thermistor, and I would very much appreciate some recommendations.
Thank you very much for your help.
RE: Hotend Thermistor Replacement Trouble
Removal must be done at temperature: 280c is customary. But wait - you say - the thermistor is dead, how do I set 280c?
Well, that is what makes 3D printing fun. Use your imagination. Some use heat guns, others bypass the thermistor, some use a drill (careful you don't remove aluminum instead of steel. But removing the heater block and using an external heat source is probably easiest. Or, buy a $10 replacement heater block.
ps: here' is a method to clamp a temporary thermistor to the block: but the thermistor is glass, so caution is required.
https://e3d-online.com/products/v6-heater-block-fixings-thermistor-clamping
RE: Hotend Thermistor Replacement Trouble
@tim-m30
Thank you so much for your reply!
The screw must be unscrewed while heated?!?!?!!??!! This really needs to be in the instructions.
If I heat the room enough, I can get the broken thermistor to be warm enough to escape from mintemp, and then heat to a higher temperature. If that works, then if I heat the heater block to hot enough, will I be able to get the screw to turn then, you think?
RE: Hotend Thermistor Replacement Trouble
@john-h64
You could try a slightly larger Torx. Important - Warm up the heating block (heat gun or possibly hair dryer). In an emergency only the disassembly of the hotend and drilling out the screw will help. I had the problem with the Mini, I drilled out the screw and replaced it with a M4 grub screw. For mounting I always use copper paste.
Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.
RE: Hotend Thermistor Replacement Trouble
- Yes metal expands with heat and it's recommended you screw the nozzle in or out at higher temperatures. Normal PLA loading/unloading should get you there. Only use an allen key that fits the screw, if you're stripping it then you're in for more trouble getting that out. What model did you buy? Your mention in here said that it wasn't like the MK3S which has the thermistor and set screw separate from the hotend with its own wires from my understanding.
RE: Hotend Thermistor Replacement Trouble
If you have an old school soldering iron, you might be able to remove the heater from the extruder and use the soldering iron to heat the block while trying to remove the set screw. But remember the soldering iron wants to be 350 to 450c ... so unless you have one you can turn down to 250 or so, use caution. The idea here is the aluminum of the heater block shrinks enough when cool to freeze the set screw and even nozzle and heat break in place.
There are also 'Easy-Out' carbide tools that may be useful to grab the set screw and turn it out if the screw is stripped.