> Not when you use shockless cutters (see my previous post on this thread)
The
> cutters produce a flat cut on one side and that means there is no wedge
> formed to push the lead back in that direction. All the energy goes into
> pushing the portion of the lead with the wedge on it. I will try some
ASCII
> art.
>
>
>                 | /
> --------------| |/  /--------
>   component   |    /  excess
>     lead      |    \  lead
> --------------| |\  \--------
>                 | \
>  <- no force   cutter  force applied ->
>                blades

Your physics doesn't add up.  If "all the energy" goes into the excess lead,
it will presumably be converted to kinetic energy of that lead causing it to
fly off.  Since the excess lead goes from still to a moving state, its
momentum was increased, which means some impulse (force over a time period)
was applied to it.  According to Newton and conservation of momentum,
EXACTLY THE SAME impulse is applied in the other direction to whatever
pushes the excess lead away.  In other words, whenever a lead flys off, a
"shock" has been delivered to the board, regardless of the cutting
mechanism.

The shockless cutters I've seen are shockless because they cut the leads in
such a way that they don't fly off.  They work more like scissors than wire
cutters.  The lead is sheared sideways instead of pinched.

This all being said, I agree that it is unlikely that trimming the crystal
lead on the other side of the board after soldering caused the problem.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.