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Hotend all junked up with PETG-thermistor wires broken  

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Steve
(@steve-7)
Trusted Member
Hotend all junked up with PETG-thermistor wires broken

I print with PETG.  Today, I got the dreaded MINTEMP error.  I typically clean the hotend/nozzle with a brass wire brush, but I must have gotten careless and broke one of the thermistor wires. The hotend is all gunked up with PETG, and there doesn't seem to be any way to replace just the thermistor short of replacing the entire hotend.  From what I have read, this is a common problem with PETG.

I have several questions:

 1) Is there any way to just replace the thermistor on a gunked up hotend?

2) Is there a better hotend I could use that won't have this problem.

3) Should I use a sock on the hotend?  Would that solve the problem of getting the hotend all gunked up with PETG?

4) Is there a way to clean the hotend/nozzle without fear of damaging the thermistor wires?

Posted : 12/06/2022 2:31 pm
JoanTabb
(@joantabb)
Moderator
RE: Hotend all junked up with PETG-thermistor wires broken

Hi Steve, 

 1) Is there any way to just replace the thermistor on a gunked up hotend?
Yes, But you have to be careful. 
Option A, remove the hot end assembly from the printer, clamp it in a vice, and heat the heatblock with a hot air gun, brush the crud off the heat block until you can see the thermistor retaining grub screw hole, then insert a suitable allen key into the holt, and loosen the grub screw, then push the thermistor out of the heatblock

Note the heatblock must be hot, or the filament gunk will glue the grub screw and thermistor in place...  

replace the thermistor and re tighten the grub screw. (Still with the heat block HOT!)

Option2,  (AT YOUR OWN RISK!) 
leave the hot end assembly in place on the printer,  remove the part cooling fan to get better access to the heat block, unplug the old thermistor wire, insert the new thermistor wire plug into the einsy board  hold the thermistor, near to the heat block, and heat the hot end  using the LCD Controls (BE CAREFUL to monitor the hot end, it will not be properly temperature controlled. )
when the filament around the hot end softens, stop heating the hotend, brush off any surplus filament gunk to expose the thermistor  grub screw hole, 
insert an allen key into the grub screw and loosen the thermistor. whilst still hot, use a screw driver or allen key, to push the thermistor out of the heat block, 
Whilst still hot, ( Or when re heated, with the thermistor next to the heatblock again) push the new thermistor into the heat block, and re secure with the grub screw.

Option C Use a new heat block, heater and thermistor...   and clean the old parts ready for your next blob...

2) Is there a better hotend I could use that won't have this problem.
The E3D Revo6 is supposed to be a drop in replacement, with a combined heatblock, heater and thermistor and nozzles that can easily be changed...

3) Should I use a sock on the hotend?  Would that solve the problem of getting the hotend all gunked up with PETG?
this is a contentious subject. I Used an E3D professional sock, on my hot end, and the next blob of doom was an epic fail. the print lifted off the heat bed due to poor adhesion, and stuck to the underside of the sock, blocking the tiny hole around the nozzle, and the printer carried on merrily pumping hot filament into the sock. 
the filament couldn't escape through the nozzle hole in the sock, so it flowed up, inside the sock, and invaded every available space around the heat block, filling the gap in the heatbreak, and gluing the  whole extruder assembly together...

I have never used a sock since
Other people report socks falling off and ruining prints, or socks degrading, and splitting with the drooping parts causing collisions.... 
Your choice, do you feel lucky, you never know, you might join the folk that think socks are wonderful... 

4) Is there a way to clean the hotend/nozzle without fear of damaging the thermistor wires?

I  heat the hot end as normal, and simultaneously use a soldering iron to carve the bulk of the blob of doom, away from the thermistor and heater wiring. 
BE VERY CAREFUL IF YOU USE A METAL BRISTLE BRUSH to clean around the hot end.  the heater on the Mk3 Series printers has 24 volts connected all the time the printer is turned on, the thermistor is referenced to ground. if the wire bristles short circuit your heater to your thermistor wiring, your einsy will be ruined.

Regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 13/06/2022 7:46 am
Steve
(@steve-7)
Trusted Member
Topic starter answered:
RE: Hotend all junked up with PETG-thermistor wires broken

Thanks for  your input.

Your comment on item 4) indicates a really bad design on the part of Prusa.  You should ALWAYS switch the hot side, not the cold side of a circuit.  I have also seen some really bad design on the I3MK3/S that is inexcusable on the part of Prusa.

For your suggestion of item 1) Option 2, this is impossible.  With the thermistor wire broken, the printer won't do anything until you replace the thermistor.  You get the MINTEMP error.  For Option 2, I tried this, but the grub screw hole was filled with PETG and I couldn't get the allen wrench into the screw.  I put the heat sink in the vise and tried this.  If I clamped the heat block into the vise, the vise would act as a heat sink and draw all the heat away from the heat block.

Can't use the Revo 6 because E3D doesn't have any hardened steel nozzles yet, and I print PETG+CF from 3DXTech.

I have another E3D hotend I will put in the printer.  I am looking for a hotend that won't have this problem.  When I put the new hotend in, I am going to try to route the wires away from the heat block.

Thanks again for your help.  I do have some socks on order, but I am reluctant to put them in.

Steve

 

Posted : 13/06/2022 2:31 pm
Artur5
(@artur5)
Estimable Member
RE: Hotend all junked up with PETG-thermistor wires broken

You must read always carefully what JoanTabb says. She’s the voice of wisdom and common sense in this forum.

That said, I’m on the opposite side of Joan concerning silicone socks. I believe that the chances of something going awfully wrong at the bottom of a hotend are ten times bigger without a sock installed. Hot filament sticks easily to metal, it doesn’t  to silicone and it’s easy to remove it afterwards. If the sock is there protecting the thermistor and heater cartridge wires, you won’t short them with the brass bristles of a brush. Melted filament won’t stick to those wires because they run inside the sock.

Yes, I know that nobody from ‘the other side’ will be convinced by my arguments. This a matter of black or white. You’re either totally pro-sock or totally anti-sock.. 

Posted : 13/06/2022 4:38 pm
Steve
(@steve-7)
Trusted Member
Topic starter answered:
RE: Hotend all junked up with PETG-thermistor wires broken

Artur5,

Thanks for the info.  I have read and processed the information about silicone socks.  I ordered 3 E3D socks from Amazon, and am awaiting them.  I'm going to put the sock on before I put the new extruder in.  However, someone suggested putting a piece of wire (with the insulation stripped).  Around the sock to keep it supported.   When I get the sock, I'll see how to do this.

 

After closely examining my gunked-up hotends, I have come to the conclusion that there is no way I could just take out the thermistor since there is PETG in the grub screw hole, and it is difficult to get it out.  I even tried that with the heater, and that wouldn't come out either.  Probably simpler to replace the entire hotend.

 

With that in mind, I am trying to locate a drop-in hotend that won't have these problems.  The E3D Revo seems good, but they don't have any hardened nozzles yet and I do print PETG+CF.

 

When I put the new hotend in, I am going to try to tuck the wires in so it is difficult to hit them with a wire brush.  I'm also going to be a bit more careful.

Posted : 13/06/2022 5:01 pm
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