On Mon, 06 Jun 2005 19:31:38 GMT, "DeepDiver"
wrote:

"Tim Wescott" wrote in message
...
SA Development wrote:

Hi,

I have some Flitz metal polish that I am using to polish the internals
of a trigger and there seems to be two ideas of thought on which has
less friction, so I thought I'd post to the metalworking group and see
if anyone here has an opinion about it.

In a metal to metal contact where one piece of metal rubs against another
piece of metal, is it smoother to polish both metal surfaces, or just one
metal surface. Some oil or grease would be used as a lubricant.

Some people think that both surfaces should be polished very smooth.

Other people think that one surface polished very smooth and the other
surface left alone is better because they think that two smooth surfaces
have a tendency to stick and catch on each other much more than one
smooth, one rough...


There are three major types of friction, and a gazillion different
materials, so both camps are probably right. You should choose a solution
that works best for your particular application.

Running friction is easy. Coulombic (dry) friction is the amount of
frictional force your parts will experience once they're moving. It's a
constant, and in the absense of liquid lubrication it's the only running
friction you'll see. Viscous drag is a frictional force that comes from
your lubricant, it goes up with speed and lubricant viscosity.

Stiction is the amount of force required to get the parts moving in the
first place, and can range from nonexistant to many times greater than
coulombic friction. Material scientists are still studying it, and they
still don't understand it very well. It's difficult to model and dang
hard to compensate for in a control system. It appears to be a function
of just about everything, and seems to involve real (albeit weak)
molecular bonds that develop between the two pieces.

If you wanted to make the ultimate friction-free trigger mechanism you'd
eliminate all sliding contact, and either run hardened steel shafts in
bronze or if you're really nuts get a whole bunch of miniature ball
bearings, one for each pivot point.


Running hardened steel shafts in bronze (or even ball bearings, for that
matter) do not eliminate sliding contact, they just reduce it.

But I don't think the OP was concerned about the pivot points in his trigger
group so much as he was concerned about the lineal sliding of the sear.

Actually, in the sear, you want some static friction as that is part of the
"break" of the trigger. But once you overcome that, you want your dynamic
friction to be minimal.

Yes, both sliding surfaces should be polished. As for lubrication, do not
use grease or oil on the sear. Use a dry lubricant (like Kano Laboratories'
Molyfilm) that will not hold dirt or other contaminants.

- Michael

I agree. Though I tend to simply use BreakFree or TriFlow on the
sears. The only weapons I worry about having too light a trigger pull
are the small bore match guns and the iron monsters.

The street guns all have intentionally firmish trigger pulls, which is
a result of springs, proper sear geometry and so forth. They are glass
smooth, but firm.

Gunner

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