Print Head Salvagable?  

Re: Print Head Salvagable?

There was no nice start
Look at Prusas WEB Shop under 3D Printer parts. There you will find what you are looking for, MK3 Hotend Thermistor.

https://shop.prusa3d.com/en/mk3-printer-parts/205-mk3-hotend-thermistor.html

Re: Print Head Salvagable?

Thanks. Looks like the Prusa Shop isn't selling them to US buyers? Is it the same as this one?
https://e3d-online.com/thermistor-cartridge

Are there any instructions for how to remove the old thermistor and install the new one?

Re: Print Head Salvagable?

Found it 🙂

http://manual.prusa3d.com/Guide/How+to+replace+thermistor+in+the+Extruder/496

Re: Print Head Salvagable?

It may be that you need to contact Prusa Support chat and ask them to unlock the option to buy spare parts for your account. Only people that have bought a printer can buy spare parts because they don't have enough to supply the entire world.

Re: Print Head Salvagable?

Tried to remove the busted thermistor, but the set screw holding it was so tight the hex socket got stripped. Plus the whole aluminum block seems to have loosened as well.

At this point is my only option to replace the entire hot end? This thing already cost $750. I'd rather not shell out another $100 if it can be avoided.

Re: Print Head Salvagable?

Did I mention the button head screw holding the heating element is also stripped? Why are these screws so tight!? There should be tight enough to not loosen over time - not so tight that it's impossible to remove them. Now instead of a $10 part, the whole thing has to come out. Definitely not pleased with my 3D printing experience so far 🙁

Re: Print Head Salvagable?

Did I mention the button head screw holding the heating element is also stripped? Why are these screws so tight!? There should be tight enough to not loosen over time - not so tight that it's impossible to remove them. Now instead of a $10 part, the whole thing has to come out. Definitely not pleased with my 3D printing experience so far 🙁

Did you try to undo them hot or cold?

When ever doing any work on the print head, do it hot.. If its cold the filament, that has seeped into the cracks/threads will act like glue

Try heating it up now to 230 degrees and you may still find you can undo them.

Re: Print Head Salvagable?

Did you try to undo them hot or cold?

When ever doing any work on the print head, do it hot.. If its cold the filament, that has seeped into the cracks/threads will act like glue

Try heating it up now to 230 degrees and you may still find you can undo them.

Good idea, but remember the problem started with my thermistor. Without a functional thermistor, all I get is a MINTEMP error and no heating.

Re: Print Head Salvagable?

Did you try to undo them hot or cold?

When ever doing any work on the print head, do it hot.. If its cold the filament, that has seeped into the cracks/threads will act like glue

Try heating it up now to 230 degrees and you may still find you can undo them.

Good idea, but remember the problem started with my thermistor. Without a functional thermistor, all I get is a MINTEMP error and no heating.

Ahh.. Yes. good point.. But you will still have to heat it.. cold PLA/PET/ABS affectivly glue.. In cases like this, you are going to need to take a hot air gun, or blow torch and CAREFULLY warm/heat it... You will never get the screws undone cold.

You could also power the hotend "heater" from a PSU.. But as there is no thermistor, it will jsut get hotter and hotter and hotter wit no control, so again, you would have to be careful

Re: Print Head Salvagable?

It's 1:40AM here, so I'll try a heat gun tomorrow. If I'm lucky the screws come out and the block and heating element haven't been damaged. Thanks for the help 🙂

Re: Print Head Salvagable?

It's 1:40AM here, so I'll try a heat gun tomorrow. If I'm lucky the screws come out and the block and heating element haven't been damaged. Thanks for the help 🙂

You may want to disassemble the hot end before doing this as using a hotgun is certainly going to melt the mount.

Good luck.

Re: Print Head Salvagable?

Definitely remove the hotend first when using the heatgun. I'd take it for granted that you damage the extruder parts otherwise.
As you have to unwind the spiral wrap anyway, you might also unplug and remove the heater cartridge cable, this makes it much easier to remove the hotend. Have you assembled the printer yourself? Getting the hotend out is a bit tricky I found and it helps for repairs if you already know how assembly works (that's why I bought a kit). Also look a the E3D hotend assembly instructions if you don't know this already.
The thermistor cartridge is difficult to remove. It is a tight fit and the set screw slightly deforms the thermistor, making it difficult to press in or remove. But even if you can't remove it, you just need the extra heat block, which is GBP 11.50 in the E3D shop. This is probably not necessary, if you disassemble the hotend, you can definitely hammer the thermistor out (unless you really botched up the set screw).
I recommend you get a sock, that would have prevented the filament mess over the heat block and the screws wouldn't be glued in by the filament.
Instead of a heatgun or lab power supply connected to the heater cartridge, you might also try a soldering iron for heating the heater block. Tin won't stick to the aluminium, so set the iron to full steam and touch the heat block with a fat tip. Don't solder the brass nozzle though...

... you're in for a steep learning curve. On the positive side, you'll get a crash course on hotend repair and you can just laugh at the next jam.

- Martin

Re: Print Head Salvagable?

I rebuilt my extruder assembly when I did my R2 rebuild. I had a stack nut that I could not get pliers on so I could not remove the extruder cover.

After I removed the cover I still could not remove the heat sink assembly without excessive force. I had to carefully cut away bits of the main extruder body with a razor saw after I got the cover off so I could remove the hot end with out excessive force. Fortunately because of the nut I had printed of a new extruder body and cover before I started.

So if you have a working printer and plan to remove the heat sink from the assembly print of a fresh extruder body before you start.

Re: Print Head Salvagable?

I think PR modified the main extruder body https://github.com/prusa3d/Original-Prusa-i3/blob/MK3/Printed-Parts/stl/extruder-body.stl in order to make it easier to remove the hotend. There's a chamfer at the top and a cutout for the PTFE tube that weren't there with the MK2 https://github.com/prusa3d/Original-Prusa-i3/blob/MK2/Printed-Parts/stl/extruder-body.stl , so this got easier. I managed to get out and re-insert the hotend without having to exchange parts, but it needs quite some force.
BTW I did this after my first jam, I replaced the stock heatbreak with a non-stick version from Micro-Swiss.

- Martin