From: Larry Margolis <margoli@watson.ibm.com>
Subject: Re: sidebars
Date: Sat, 05 Sep 1992 02:50:14 GMT
Reply-To: margoli@watson.IBM.com
Disclaimer: This posting represents the poster's views, not necessarily those of IBM
Organization: The Village Waterbed

In  <1992Sep3.092217.5040@cubetech.com>  andrew@cubetech.com (Andrew Loewenstern) writes:
> In article <star.715206733@husc9> star@husc9.harvard.edu (Joshua Star) writes:
> >I don't understand exactly how a sidebar works.  The way I understand it,
> >tension on a plug of a lock with a sidebar doesn't put tension at the
> >shear line ... therefore not producing a ledge to hold the picked pins on.
> >But the sidebar must somehow know when the key is inserted, and the pins
> >are effectively picked... how does it do this if no tension is at the shear
> >line.  In other words, the way I see it, something must put tension at the
> >shear line when the plug is (tried to be) turned.  So how does a sidebar work?
>
> A side-bar is more like a comb.  It's a bar with little 'fingers' that
> stick out.  The fingers each fit into a small hole in the side of each
> pin.  The sidebar blocks the plug, so the bar has to retract into the
> holes on each pin before the lock will open.  Since the bar is just
> that, a bar, it won't retract until _all_ of the holes in the pins are
> at the right level.  This is what makes it harder to pick.  But since
> the pins aren't all the exact same diameter, it's not impossible.
>
> On Medeco biaxial locks, each pin has to be *rotated* as well as
> lifted to the correct height before the lock will open.
>
>
> I'm pretty sure this is how they work, but hey, it's 4:20 am.  If I'm
> wrong then Larry will be swift to correct me... ;-)

You rang?  :-)

On all Medeco locks, the pin has to be rotated as well as lifted.  On
the smaller cylinders used in tight areas, the sidebar works as you
describe - the pins have holes in them, and the fingers of the sidebar
are round in cross-section.  The holes in the pins account for both
the height and rotation.  In the standard Medeco cylinder which you
find on doors, there is a normal shear line on the pins that accounts
for the height, and a separate sidebar for the rotation.  The bottom
pins have notches in the sides, and the fingers of the sidebar are
tall and thin in cross-section in order to fit into the notches.  There
are three possible notches, corresponding to a left, right, or center
cut, and the pins have one deep one that lets the finger in and the
other two locations have shallow notches to help prevent picking.
The Medeco biaxial locks add one more variable - they allow each
pin to be off-center (forwards or backwards) from the normal pin
position.  This allows for more different key combinations, but doesn't
really affect security.

Other sidebar locks which don't use both rotation and height don't
have fingers.  The sidebar can be simply be a round rod (Fichet) or
have a wedge-shaped end (GM sidebar) running the length of the plug,
which fits into a corresponding notch in the side of the wafers when
they're raised to the correct height.  When all the wafers are at the
right height, the sidebar retracts into the plug and you can turn it.
Without the key inserted, if you try to turn the lock, you wedge the
sidebar between the plug and the shell, and the plug is prevented from
turning.

Larry Margolis, MARGOLI@YKTVMV (Bitnet), margoli@watson.IBM.com (Internet)