thermistor and heatsink compound

I've just bought a new thermistor for my 3-D printer hot end the previous person who owned the machine put heat sink compound in the hole where the thermistor is located does this contaminate the sensor and give false readings or should that be fine please bear in mind that there is a 2mm bear wire gap from the sensor to the start on the insulation

please not if a was to use heat sink compound it will be the white stuff

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hello

My guess is that it won't significantly affect the readings but it very much depends on the heat sink compound, some can be very conductive - e.g., Arctic silver, others less so. Unfortunately, hotends work in the temperature region where most compounds become somewhat more conductive than at room temperature. In most cases, this won't matter; but look at the specification sheets to see if they at least brag about low electrical conductivity.

Mike

Heatsinks normally don't get much over 60-70C.

It seems unlikely that heatsink compound of any type is intended to work at hot-end temperatures, and will probably decompose quickly (accompanied by dripping, smoke, and stink). I always use antiseize compound (from auto parts store) on everything that is mounted in the heater block. I'm not sure it's intended to be used at hot end temperatures, and it does smoke at first, but it has always prevented the screws/nozzle/heatbreak/thermistor/PT100 sensor from getting locked in.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

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the_digital_dentist
Heatsinks normally don't get much over 60-70C.

It seems unlikely that heatsink compound of any type is intended to work at hot-end temperatures,..........................................................................................

I disagree

[reprapworld.co.uk]

Note that I know nothing about this compound's electrical resistivity at hotend temperatures as my hotends use thermocouples for temperature sensing and these are relatively insensitive to electrical leakage.

Mike

... for higher temps you can use "prestogum exhaust repair paste" -- should be stable for much above 300°C (had a version specified with up to 800degC, but actual ists reduced in specs to max. 600degC) ... should have better thermal conductivity, if mixed with metal powder, but could have disadvantages when oxidizing the powder before sintering, so better with "precious" metal powder (have small amounts of silver, gold and platinum thermal glues too ... silver is not sufficient with "aggressive" ambient containing NOx) ... or something like brazing pastes, used for jewelry or such ...

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Viktor
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leadinglights

Quote
the_digital_dentist
Heatsinks normally don't get much over 60-70C.

It seems unlikely that heatsink compound of any type is intended to work at hot-end temperatures,..........................................................................................

I disagree

[reprapworld.co.uk]

Note that I know nothing about this compound's electrical resistivity at hotend temperatures as my hotends use thermocouples for temperature sensing and these are relatively insensitive to electrical leakage.

Mike

I use boron nitride paste, but I don't pay that obscene price for it. It's good to 850C. The only complaint I have about it is that it is water based, and doesn't really want to stick to anything. Once it's dry, it's kind of a chalky powder, and doesn't conduct electricity at any temperature within its useful range (when dry). Even when still wet, it's not conductive enough to cause any damage to heaters or thermistors.