Thermistor cartridge keeps coming loose

Discussion in 'E3D-v6 and Lite6' started by brucehvn, Oct 30, 2018.

  1. brucehvn

    brucehvn Member

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    I have an e3dv6 with the latest heater block and thermistor cartridge. I had an issue where the temperature would just start fluctuating a lot and sometimes causing a thermal shutdown. It took me some time, but I found out it's because the thermistor cartridge had come loose. Last week I tightened it back down following the instructions, just getting the grub screw to touch then 1/8 more turn of the hex wrench. Now after just a week or so of prints, it's starting to come loose again. I don't want to overtighten it like the instructions warn against, but how can I keep this thing from coming loose all the time?
     
  2. Old_Tafr

    Old_Tafr Well-Known Member

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    Unlike the heater the hole for the thermistor does not have the benefit of a slot to aid tightening and tightening the grub screw into the thermistor is as suggested not a good idea.

    Several possibilities; the thermistor is too small a diameter.......... the hole is too big........ a combination of both, or maybe the thread in the block is not cut deep enough and the pressure you feel is not the screw tightening against the thermistor but the screw binding. Equally the grub screw could be made slightly too big, i.e. thread not cut deep enough. (ok for the purists the grub screw thread is probably rolled not cut)

    The grub screw could therefore be feeling tight before it hits the thermistor. Try removing the thermistor and checking that you can screw the grub screw in until it can be seen by looking down the hole where the thermistor fits.

    Take care if the grub screw is short it may exit into the hole, so only screw it just enough so that you can see the it appear. Or you could use a longer screw with the same thread.

    If the screw can be seen ok without it feeling tight, then either the thermistor is very loose in the hole or maybe the leads are too tight and pulling on it as you print?

    If all looks good then maybe slightly more than 1/8 just so you feel the screw press on the thermistor without damaging it.

    I am tempted to say use something like locktite (a tiny tiny amount otherwise you may glue the thermistor {not the screw} in permanently) on the screw but as this does not appear to be a common problem you need to investigate what is wrong first.
     

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