[time-nuts] Brass Screws

John Ponsonby jebponsonby at gmail.com
Wed Jan 18 06:15:39 EST 2017

Re: Brass screws
	Brass is not only to be avoided because of residual ferromagnetism but is also unsuitable for use in ultrahigh vacuum because zinc has a high vapour pressure. In an H-maser I used beryllium-copper BeCu for small screws and springs, aluminium-bronze for larger components and of course pure Al. BeCu requires special care when being cut as it is toxic, but finished items are safe to handle when all microscopic swarf and filing "dust" has been removed. I think magnetic instruments, such as steering compasses, magnetometers etc are traditionally made of bronze. I have an invaluable but very simple and sensitive astatic-magnetometer supplied by the Danish Meteorological Institute in Copenhagen.
John P

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