Thermocouple repair vs. replacement?

[John Sondericker]

My thermocouple wire broke right where the wire enters the heating block at the point where the "strain relief" shrink tube is located. Knowing a thing or two about thermocouple wire is it feasible for me to just twist and crimp a new thermocouple junction and place the wire back into the heater block and call it good? Do I really need to replace the full wire?

Thanks,

J

[Jetguy]

Replace it. Seriously, the issue here is it's single strand wire that
broke from repeated flexing. This means you should assume the entire
wire has been "work hardened" and therefore, likely to break again.

[James McCracken]

the thermocouple is made from two wires that produce a voltage at their junction depending on the temperature.  Actually, all conductors produce a voltage when under a thermal gradient; the thermocouple uses two different metals to ensure that there is a DIFFERENCE in voltage between one side and the other - the difference can be as little as 1 microvolt per degree (up to about 70 microvolts per degree)

In order for them to operate correctly, the two legs of the thermocouple need to be the same length and similar metals.  For this reason, I would avoid "just twist[ing] and crimp[ing] a new thermocouple junction" as this will result in new metals and conduction paths in the hot part of the thermocouple.  As you can see at the diagram http://en.wikipedia.org/wiki/Thermocouple on the right side of the wiki article on thermocouples - you want the join to your measurement equipment to be at a cold junction, not in the hot zone, for best accuracy.

If you feel like trying it, you can certainly do so faster than you could order a new one.  However, I would want to be very sure the temperatures its measuring are accurate when done.

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[Jwo Fox-Lee]

I've successfully joined my thermocouple back together after the cats chew it in two.

The temperature of the heater block still matches the heated platform thermocouple at room temperature, so I'm pretty confident it's working.

Plus, I've been printing for 50+ hours now without any issues.

- Jwo Fox-Lee

[John Sondericker]

Yes, in my experiences thermocouple wire -- the entire length -- a two dissimilar metals. I've always just cut a length the what was needed and twisted and crimped the ends to form a junction from which I can read temperature.