agraffes on - agraffes off

[Phillip L Ford]

On Tue, 11 Dec 2001 16:33:29  
 Ron Nossaman wrote:
>>Yes, I knew that.  I just thought I'd take the opportunity to change the 
>>subject.
>>
>>Phil F
>
>Why? These are reasonable enough questions without needing to be diverted.

Sorry, Ron.  I should have started a new thread.  I didn't mean to imply that
your question wasn't reasonable. Reading your post just caused
me to think of something I wanted to talk about.

>I'm curious as to how both alignment and height are addressed by the
>rebuilders out there in rewhatevering land.


>Ron N


I don't worry about height differences.  The only reason I can see to worry about it is
because of regulation concerns.  Even good quality actions have so much part and
geometry variation that I can't believe a few thousands difference in blow distance,
overcentering, or let-off is going to make a difference in feel that is greater than the
inherent note to note variation that is already there.  I think it is in the noise.
The agraffes that I seem to get these days have a pretty agressive undercut on the
shoulder and a pretty thin ring around the edge of the shoulder.  The consequences of
this are:
A little cinching down puts a lot of contact pressure between the agraffe and the plate,
so you don't need a lot of cinching down to make a firm connection.
It tolerates a lot of cinching down because it doesn't take a lot of load to deform the ring
around the edge of the shoulder.  My experience is that you can get considerable change
in angle from the point where I consider the agraffe to be tightened down firmly enough
and the point where it would break off.  So my practice is to put in an agraffe, see if it's
even remotely in the ballpark alignment wise, and then cinch the hell out of it if need be.
This may not sound like a good idea, but if you check a bolt or fastener book you will
find that in fastener applications for cyclic load you want a lot of preload so that your
nominal stress is high and the ratio between high stress and low stress under cyclic
load is lower.  This gives you better fatigue life.  The downside is that occasionally I
will break one off.  Your idea of making a little tube so that you don't have to put
the agraffe in all the way seems a good idea but I find that in practice I don't take
many of them back out.  On those few that I just can't seem to get in the general
ballpark before cinching down - I will take a machine tool file (I don't actually know
the name of it but it is a metal plate that has been sputtered to roughen it.  They're
using for touching up edges of machine cutting tools) and take a little off the agraffe
shoulder.  I really can't see that it needs to be machined so that it is perfectly flat.
The shoulder ring has so much compliance it's going to flatten out anyway.
So, there you have it.  Not a pretty picture.  Nothing like the textbook version.

Phil F