Adhesive for assembling hot end.

[darus67]

I've been wondering about the RTV Silicone commonly used for gluing the resistors and thermistor in place
on the hot end.

The Permatex Copper stuff that is commonly available is able to withstand high temperatures,
but it isn't intended to be thermally conductive. You're basically placing a layer of thermal insulation
between the resistor and the body of the hot end, and between the thermistor and the hot end. That
makes precise temperature control difficult.

I considered trying the metal filled JBWeld epoxy, but that doesn't have the high temp rating, and
it is rather permanent.

Arctic Silver makes thermal epoxy, but it has the same issues as JBWeld.

Has anyone experimented with any other thermal adhesives?
Does it really make any difference?

[Eric]

In your search for alternate thermal compounds, make sure they aren't electrically conductive...that could really screw up the signal if they touched the leads.

I've looked at assembly videos for a few other hotends.

In one case, they simply strap the thermistor bulb firmly to a flat outside surface with wraps of Kapton tape, and it seems to work.

In another, they screwed the thermistor to the head (the same thermistor can be bought pre-crimped in a ring lug). This approach should work for the CNC hotend if you threaded the thermistor hole.

[michaellatif]

In one case, they simply strap the thermistor bulb firmly to a flat outside surface with wraps of Kapton tape, and it seems to work.

That's how I hold the thermistor in place, Kapton tape. The resistors are rolled in foil, gently pushed into the extruder head and then excess is trimmed off (this part is a little tricky and require constant testing to make sure the foil is not touching the resistor leads) with RTV capping the ends. This guarantees me the best thermal transfer.

[stienman]

I used quiksteel, a high temperature metal repair compound that seems to be composed of metal filings and epoxy. I expect it's conductive, but haven't tested for that. I just applied it carefully and tested for shorts after. Seems to be ok. I don't look forward to the day I might have to red roll those holes out when the components fail though.

I have another hotend on order from a kickstarter project so I'll always have two, since it's hard to print parts to fix a machine that can't print parts, and in all build logs I've read the hotend seems to be the weak point of any machine. The new hotend has a cartridge heater, so that part should be nicer to deal with.

[darus67]

I broke down and assembled my hot end with tinfoil and red RTV.
The metal filled epoxy just seems too permanent.
I followed a tip I read somewhere that suggested dipping the full length of the resistor and thermistor leads
into the tube of RTV so they are insulated electrically. Once that had set up, I rolled the resistors in foil
and capped them with silicone. Then I used a toothpick to fill the thermistor hole with silicone, then stuck the thermistor in place. That's all curing now. Hopefully I can give it a try tomorrow.

[tom10122]

I broke down and assembled my hot end with tinfoil and red RTV.
The metal filled epoxy just seems too permanent.
I followed a tip I read somewhere that suggested dipping the full length of the resistor and thermistor leads
into the tube of RTV so they are insulated electrically. Once that had set up, I rolled the resistors in foil
and capped them with silicone. Then I used a toothpick to fill the thermistor hole with silicone, then stuck the thermistor in place. That's all curing now. Hopefully I can give it a try tomorrow.

Monitor your temp VERY carefully, you just insulated the thermistor and your temperature will be hotter.

[darus67]

I bought a DMM with a thermocouple just for that purpose.
According to it, the Velleman holds temperature within about +/- 5° C.
I held the thermocouple against bare metal in the hole opposite the one the thermistor is in.

Unfortunately the thermistor popped out of its hole rather easily after I got done temperature testing.

I'm going to have to re-think my thermistor mount.

[BrainSlugs83]

Unfortunately the thermistor popped out of its hole rather easily after I got done temperature testing.

I'm going to have to re-think my thermistor mount.

Glue it back in, and throw some Kapton tape over it for good luck.