[GreenKeys] What is this surface treatment?

[Keith Lueck]

 Hi Larry - 
The stippling on the plate is called "planishing", and is a manufacturing thing, to get the disk real flat. If you pressed a bent disk between flat dies, it would spring back and retain some of its warp. The stippling permits plastic deformation of the disk, even if initially flat. You will see this on telephone relays and other stamped assemblies for the same reason.
(I didn't originally know this - I learned it from a youtube video...)
Here's a Wiki entry on it: Planishing

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Planishing

This is done by hammering with a planishing panel hammer or slapper file against a shaped surface called a plani...
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Keith

    On Monday, September 14, 2020, 05:03:10 PM CDT, Larry Goga <lgoga at swcp.com> wrote:  
 
 Hello All,
I added this question to a message I replied to this weekend from GreenKeys.  The message thread was about “WD-40” and I received only one reply, which didn’t answer my question.  So I’m sending the question again in its own messsage thread.
In the attached photo you can see a flat metal plate in the lower left corner.  The surface of the metal plate is covered with systematically spaced tiny dimples or “pin pricks”.  I have seen this surface before in all sorts of mechanical devices.  In this case it’s in a teletype machine.  My questions are: what is this surface treatment called, why is it there and what does it do?
Thank you everyone,
Larry, AE5CZ

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