thermocouple problem

[courtjester22]

Hi
I am building my first oven and have a problem with the thermocouple I bought. This is a small probe with a threaded part to hold it in place. I though it was to be screwed into a hole for the tip to contcact a surface for heat transfer. Well the threads are not metric or english (close to 1/4 X 20)
Well I broke the threaded part (cheap brass bad fit). I have another on the way but need to understand how I should mount it. From other posts it seem the probe may be mounted to a bracket in the oven and floating in the threaded part.
Is this true?
The thermocouple is a type "K" came with the PID and SSR I'm sure other have the same setup and it has worked great for them. need to know the threaded size if posible?

Have fun
Tom

[gcdrummer02]

JB Weld should do it

[courtjester22]

Your right

I have used that stuff inside a vw head exhaust without fail.
I want to use a nut the would fit the threads but I guess the manufacturer had problems reading the specs and just cut some crazzy thread pattern.
thanks for the reply

have fun
Tom

[dix17]

welcome to the crazy world of mix matched pipe fittings, I guess its an npt (national pipe fitting) size just measure the thread diameter then look up its npt size is it a compression type?

[courtjester22]

Thanks for the reply
but no cigar npt are tapered and that small would be much finer threads..
have fun
Tom

[CarWiz]

Got your message, I'll just answer it here.

All of mine have been 1/4-20. And yes, they are pretty thin. I had to make a new housing for one of mine after mounting it too tight. After that I used a lock washer on the rest and tighten just enough to compress the washer. Don't throw the TC out. If you have or know someone with a lathe, you can make a new housing out of a 1/4-20 x 3/4" bolt.

You are correct. The TC should be mounted so that the tip is in free air. Preferably, near where your parts hang or near the center of the oven. I've got the PC oven TC mounted on a swinging L-bracket. I can move it to load the oven then swing the TC close to parts. BUT... I also have the TC shielded wire insulated with a fiberglass sleeve. It may not need it but I had the sleeving and it made me feel better.

If you mount the TC through the wall, it may take longer to respond to heating/temperature changes. Most walls are HUGE heat sinks. And when they get hot, they continue to radiate the heat to the TC even when the heating element(s) may be off. It's best to keep the TC away from a wall a few inches and have it in moving air currents. A simple bracket can accomplish this but don't make the bracket out of too heavy of metal. A strip of your wall material would work.

Hope this helps and answers your question.

Ken

PS - As far as making a new housing for the old TC, you really don't even need a lathe. You just need to be able to drill down the middle of the bolt. Mark the wires for red/blue and clip off the wire terminals. You'll need to feed the wire through the end of the bolt then reattach terminals.

[courtjester22]

Thanks Carwiz

I still have the TC and checked it both with a Multimeter (mvolts in the home oven) and then hooked to the PID and it seems to work fine. I removed all of the bolt section and will use a simple hold down to a thin bracket in the oven.
I have some thermo insulation for a spark plug wire I will cover the braided wire out of the oven.
have fun
Tom

P.S. still driving the model "A" street rod

[CarWiz]

P.S. still driving the model "A" street rod

I wish! The avatar is car I did for a customer. It's a "little-bit" modified 31 Ford Tudor. Me? I drive junks.

[courtjester22]

here is a 30 I built and sold as shown in the pictures .
love dem street rods.

have fun
Tom

[JTW37]

Welcome aboard Tom
Your avatar looks like my 31 Chevy. Want to sell it, but wife says to make it a Rat Rod.