PSN-L Email List Message

Subject: Re: shim stock hinges
From: George Harris gjharris@.............
Date: Thu, 16 Mar 2000 12:52:26 -0500

S-T Morrissey wrote:

> Regarding shim stock for hinges or flexures:
> In the event that C&H sells out of the shim stock that Jim has
> posted info on, it can be obtained from McMaster Carr Supply
> (630 833 0300): (MC, VISA, by UPS)

Recently, I have located sources for thin beryllium copper which I
consider the ideal material for hinges.
The sample which I have is .002 thick, and has a strength of 70,000
psi.  By heat treating at 600 deg. F
for a couple hours, the strength is 150,000 psi.  Due to the fact that
the modulus of elasticity is about
60 % of steel, the hinges are more flexible.  It is also fully
solderable after removal of the thin oxide.
By having a simple fixture, the part can be formed in the soft
condition, and it will retain any shape after
hardening.   As an example, the parts which are 1/4 inch wide by .002
thick have an "S" shape to fit
around a 1/2 in. rod and have an elastic limit of 75 pounds each.

In order to heat treat it, I have constructed a tiny oven of firebrick
which is placed on a gas range with
a thermocouple sensor.

I would consder making hinge springs for others at minimal cost if we
can agree on a configuration
which would be generally useful.  The present springs are designed to
fit around two 1/2 inch cylinders
placed .7 inches apart, and be fastened by 4-40 screws on the far sides
of the cylinders.  The mounting holes are 1.67 inches apart, so that a
pair cross at 90 degrees when mounted in opposite directions.  Tabs of
approximately 3/8 inch on each end can be used to conduct currents of
any reasonable magnitude.

George Harris - Benicia, CA


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Larry Cochrane <cochrane@..............>