Key pins and key bushings

Newton Hunt nhunt@jagat.com
Fri, 28 May 1999 08:48:45 -0400


> When you turn a front rail pin you inevitably get a smaller contact surface than if the pin "flats" were parallel to the bushings.

Ron, think about this.

Take a pin and cut it and look at it's cross section, you will see
what I mean.

The pin is shaped like a ball with the center section removed.  This
is effective and inexpensive to produce.  Rotating the pin to take up
some lost motion is perfectly acceptable unless the bushing is
severely worn.

The only time you will get a smaller contact area for the bushing is
if the pin has a parabolic curve (absolutely useless and VERY
expensive to produce) or a pin with a cheap rectangular cross section.

The radius of the pin is constant on both sides so a rotation of the
pin will present a constant tangent to the bushing _until_ _that_
radius terminates.

I prefer to rebush key myself because I do a better job than most but
I still get some variation of fit which I will equalize by turning the
pins slightly.

Most pins do NOT have a consistent vertical shape so I test bushing
and pin fit at the rest and depressed positions.

		Newton



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