Attaching heaters and thermistors to hot-ends

Just a quick question - how is everyone attaching the heaters and thermistors to their hot-ends? I assumed that some sort of high temp glue was the norm, but does that make it difficult to change them if required?? I was considering the "plumbers tape", which appears to be high temp resistant and can be easily removed if required, but would that be secure enough - assuming it is wrapped tightly.

Any thoughts or info on what others are doing would be much appreciated.

Colin

Well everyone may have their own ideas but I used exhaust gasket cement to locate the heating resistor and a small wrap of kaptron tape to secure the thermistor. I can change the thermistor easily if necessary and I figured if the heating resitor needed changing it would be wrecked anyway so chipping or drilling out wouldn't matter.

Ah hah, good old exhaust goo - great idea. I've heard of glass cement also, not sure how easy it is to come by and of course fire cement. But of course I only need such a small amount it doesn't seem worth too much effort in tracking down some of them.

Thanks Oatridge - found this at Super Cheap Auto's. Comes in a reasonable size tube for around $9 and is good for up to 300 deg C

The very brand I have used, seeems ro work Ok.

You can also wrap the hotend in "self vulcanizing silicon tape", some are heat resistant (specs says up to 260°C).
It will help secure the "legs" of the components while providing some heat and electrical insulation.

I've bought some online but didn't have time to test it yet.

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

Is anyone using heat transfer paste when sliding the resistor/heater into the hole on the head? I was thinking of doing that with a dob of the high temp glue at each end and then it should be easy enough to take apart.

So, would cement be needed if nichrome wire was used instead of the ally' block?

Cement is required with nichrome wire and with resistors. There has to be a thermally conductive bond. Any air gap will cause the resistor to overheat and fail. Wrapping the resistor in just the right amount of aluminium foil and jamming it in works, but as I cement the thermistor anyway I use that for the resistor.

I don't think there are any heat transfer pastes that are rated for the temperature. Normal heatsink compound dries and and turns to dust.

When the resistor is cemented in they never fail, so there is no need to be able to remove them again. I expect it could be knocked out with a punch but I have never needed to.

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[www.hydraraptor.blogspot.com]

I use high heat silicone, works perfectly and never had a failure yet

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Experimenting in 3D in New Zealand

Hi All,
I made the silly mistake of using some heat sink paste on my thermistor. Unfortunately the paste was silver based and highly electrically conductive as well as thermally conductive. The result was it shorted out the thermistor and messed up the temperature reading.
It's awful stuff to clean off too.
So now I don't use anything for the thermistor. It sits deep down in a hole and there is practically no lag from having it surrounded by a little bit of air.
It is kept in place by a bit of Kapton tape wrapped around the the heater and thermistor wires and the PEEK insulator.
I don't use any paste or fire cement on the heater either but my heater is a cartridge type. It is 6 mm diameter and I have it in a reamed 6 mm diameter hole. It slips in easily but there's not much of an air gap. I bypassed the wire wound thermistor approach when I read about the issues people were having with them burning out.
You can't see a lot in the picture because my hot end is wrapped in silicon foam but you can see the heater here http://www.makershop.co.nz/heater-6x20-25W
In the interest of full disclosure that is my website and I am selling the heater cartridges.

If you do need to use something to glue the wirewound resistors in place then you could try a hi-temp silicone. These are usually rated for continuous operation at up to 300°C or up to 350°C intermittent.
Silicone rubber won't be as good at conducting heat as metal but it will be a lot better than an air gap and if need be it should be easy to clean out.

All advice is offered with the best of intentions but without warranty.
Regards,
Mike Paauwe

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Makershop - Reprap parts, adding new stock almost daily.
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Thanks Mike, nice website, some good stuff there with reasonable pricing.

I did buy some silicon heat transfer paste from Jaycar but have yet to try it out - maybe I'll skip it. The J head I have is a reasonable fit for the heater resistor anyway. I might measure the hole and see if your heater unit fits too.

I bought some Loctite Copper Maxx Silicone from Repco that looks like a good product for mounting resistor heaters or thermistors.

It is an RTV silicone in an 85g tube. High temp resistance of 316°C
Full cure to 3mm depth in 24 hours.
It appears to have copper particles in it which should make for good thermal conductivity. The spec sheet says it is a good electrical insulator so it won't affect thermistor readings.

Loctite 5920
http://www.henkel.com.au/aue/content_data/283618_gasketing.pdf

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[www.makershop.co.nz]
Makershop - Reprap parts, adding new stock almost daily.
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Watch out for that stuff, if the resistor outer fails you can end up with a short caused by the copper in it. I've seen comments in other parts of the forum about it.

The manufacturers spec states clearly it is not electrically conductive. But I have not verified this myself.

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[www.makershop.co.nz]
Makershop - Reprap parts, adding new stock almost daily.
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