Re: Clock or anemometer?


I agree Eric, but the problem with epoxy is the TC. As i recall the TC of epoxy is about 10x that of invar.
Ive been thinking about this a lot, and it is very very difficult to arrange the joint so that movement of the epoxy (with temperature) doesnt change the pendulum length. This is the advantage of the pin through the rod method.
With epoxy joint (at the suspension end)i think it must be arranged so there is clearance between the end of the rod and the suspension body. That way, when the epoxy changes length, an equal amount of movement occurs above and below the centre of pressure of the joint.
Ill do a drwg if this is not clear from my convoluted description.
The same would apply at the bob end. 
Interedted in your view.

On Sat, 4 Apr 2020, 5:09 PM Eric Scace <eric@...> wrote:

On 2020 Apr 03, at 22:08 , Eric Scace <read@...> wrote:

Neil —

   I would suggest attaching the bob to the glass with modern epoxy or even Gorilla Glue. Not only do you avoid the complexities of drilling glass (and introducing micro-fractures at stress concentration points), the joint will be less likely to move than a pin.

— Eric

On 2020 Apr 03, at 19:09 , neil <njepsen@...> wrote:

Hi Bepi,
                Its good to hear from you again, and that you are well. My wife & I are also in lockdown, and staying home 24/7.
Fortunately i am abale to continue work on my clock. i received a 1m length of Quartz glass 10 days ago and have dismantled the clock, in preparation for replacing the invar pendulum with quartz galss, and a below the bob aluminum temperature compensator, as described in Matthys's book "the accurate pendulum".
At the moment I have a 14lb bob hanging on the glass, to test the means of attachment, which is not easy.  I was intending to drill a hole thru the rod and use a pin, but because of the lockdown, I am unable to access a diamond drill, so will probably use expoxy or epoxy/carbide dust as an adhesive. Not as good, but needs must.

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