Bimetalic domes

I wonder if one could paint the convex face with fingernail polish as an etch resist and put the disc in an etching solution to thin the concave side? Would the relatively smaller 'concave mass' shift the trigger temperature upwards?

--Winston

Heaven knows, I don't like reinventing the wheel, but unless you can find documentation (such as a patent) that explains in detail how these devices work, and how a particular temperature is set, you're going to have to experiment.

I again recommend looking for one of those interchangeable thermostats. Perhaps ripping it apart will reveal the secret!

The Presto "Control Master" has been around at least 40 years, and Presto is still making appliances that use it. (I don't know whether the internal design or operating principles have changed. The probe part does appear to be longer and narrower in the current version.)

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I have been waiting for someone to suggest that the temperature at which they switch is controlled by how domed the discs are. At least that is my guess. Suggest you get some rubber and a ballpein hammer. Test what the temperature is that one switches at, and then make in a bit more domed and see if that changed the temperature at which it switches. My guess is that more domed means more change from ambient temperature before it switches.

Dan

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I have been waiting for someone to suggest that the temperature at which they switch is controlled by how domed the discs are. At least that is my guess. Suggest you get some rubber and a ballpein hammer. Test what the temperature is that one switches at, and then make in a bit more domed and see if that changed the temperature at which it switches. My guess is that more domed means more change from ambient temperature before it switches.

Dan

I will give it a go with large ballbearing in a cup and a press. But the full range of temp (10 to 220 deg C at least) switches all come in the same size package and the internal spaces and activation pins are the same dimensions including degree of doming, all that changes is the materials or construction within the domes. Normally open for the same temp normally closed is simply just the same dome in, the other way up

Another thing to try is local heating and quenching in order to change the distribution of internal stresses in the dome.

It's bimetal; I don't think you want any "unexpected" stresses.

Isaac

Pretty difficult to calibrate that change. I'd try mounting a small coil spring so as to work with or against the direction of the snap. A setscrew can then be used to modify the spring preload and adjust the snap point.

--Messed around with these ages ago. The delta-T for the flip is inversely proportional to the radius of curvature; i.e. greater radius translates to smaller temp changes to make it flip. I was working on what I call a 'kinetic solar cell' which works very well in theory...