Bimetal strip (NOT sawblades!)

[John HaineParticipant @johnhaine32865]

I’m considering the use of a bimetal to temperature compensate a pendulum.  Does anyone know of a source for small quantities please?  I could buy a few kg of the stuff from Ali but that’s too expensive and far more than I need!

Or, a reliable way to make it?

One can buy little handles with a length sticking out made for school science experiments which appear to be steel and brass strips rivetted together – I was wondering if a similar approach could be used but with pop rivets?  Epoxy to join two strips is another thought but since by definition the material is put in shear by temperature changes it might not last very long.  Soldering is another idea using a solder paste but I imagine the resulting strip would bend like a banana as it cooled.

The idea is to have a length sticking out at right angles from the the pendulum with a small weight on the end that moves up or down as temperature changes.  Philip Woodward used this on a clock but the surplus supplier he used is long gone.

[Roderick JenkinsParticipant @roderickjenkins93242]

I have a 24 x 5 cm strip of bi-metal labelled TRUFLEX P675 R TM2.  I am happy to lop a bit off for you and pop it in the post.  How much do you need?

Rod

[John HaineParticipant @johnhaine32865]

That’s exactly the material that Philip used!  Many thanks for the offer Rod, please could you spare a 1 x 24 cm strip please?  My pendulum is longer than his and has a much bigger bob.

[Roderick JenkinsParticipant @roderickjenkins93242]

Hi John,

No problem.  Send me your address via a personal mail on the forum.

Cheers,

Rod

[John HaineParticipant @johnhaine32865]

Done!

[MacolmParticipant @macolm]

Many years ago, I needed to compensate a microwave device for thermal expansion. It was for aircraft use, and had to tolerate vibration but also had to be very light. There was a good range of bi-metal sheet material available then, and there must be more today with millions of mechanical thermostat blades punched out of it.

The configuration I ended up was a circular washer, which maximises the stiffness for a given amount of temperature deflection. If applied to a pendulum bob, it would be like this diagram. In order to “flatten” minor distortions in the bi-metal washer, it needs a sufficiently strong spring force to get contact all round the outer circumference. Provided nothing bottoms out, this does not affect the temperature sensitivity.

You do need to calculate the compensation needed from the expansion coefficients of the pendulum materials. If the worst comes to the worst, it is possible to stack several disks in series, though this spoils the simplicity of the design.

 

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