[Elecraft] K3: machined concentric knobs from Mouser

[Vic K2VCO]

Wayne Burdick wrote:

> It's true that our knob manufacturer used the wrong material for one  
> early batch of the dual concentrics. But we caught most of them,  
> rejected the rest of the stock, and we've been replacing them in the  
> field as quickly as possible. The correct material is very strong, as  
> you'd expect.

Years ago I worked in an injection molding factory. There are multiple parameters that you 
have to set on the machine: temperature, pressure, time, cooling, etc. and some of these 
have 'profiles' -- they are not simply scalar quantities, but vary over time.

Different materials, sizes and shapes of products, kinds of molds, etc. require different 
setups. I'm sure there is a science to it, but I remember it being a black art. If you 
didn't do everything right you got all kinds of defects, including parts that seemed OK at 
first but later became brittle.

I remember an incident in which our engineer took some sample kitchen faucets that we'd 
made to show them to a distributor. When he demonstrated the quick smooth action of one of 
the valves...snap. The stem broke off in his hand. "Hmm, that never happened before," he 
said, and turned the other valve. Snap.
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco