Specifications

each size. Three depths would make
the space at the top of the control
sleeve .090”.
What appears from this front view
to be a slightly raised surface at the
top left of the control sleeve, would
actually be two slightly raised surfaces
if viewed from the top. The two raised
spots are located to the left of each of
the two pin chambers contained
within the control sleeve. Those
features did not exist on the original
version of the control sleeve for the
Medeco I-Core, but were added in a
design change in early 1992. The
original version had some problems
with cores that had #1 size master
pins in the chambers contained within
the control sleeve.
As the lock and the pins started to
wear over time, the gap between the
shell and the control sleeve would
sometimes allow thin #1 master pins
to slip out or jam. The raised surfaces
in the redesigned control sleeve were
made to keep those thin pins from
slipping through. If you ever run into
any pre-1992 Medeco I-Cores with that
problem, you can order just the
control sleeve and salvage the rest of
the existing core. If you are not using
any #1 master pins in those two
chambers, the problem shouldn’t
occur. In that case you don’t
necessarily need to replace the old
control sleeve.
Illustration 2, shows side cutaway
views of the Medeco I-Core to
illustrate how the control sleeve
works. On the top is the core with an
operating key. All the pins are lined
up at the operating shear line, which
allows the plug to rotate and operate
whatever lock mechanism to which
the core and housing assembly is
attached.
The illustration on the bottom is a
core with a control key inserted into
it. The control key cuts are the same
as the operating key in all positions
except for the third and fourth. The
third and fourth position cuts are
exactly three depths shallower on the
control key than on the operating
key. That causes the top surfaces of
those two pins to be raised three
depths higher. I’ve already indicated
that the thickness at the top of the
control sleeve is also the equivalent
of three depths thick. This effectively
creates a two tiered shear line. The
two pins at the front and the two pins
at the back of the core are at the
normal shear line, while the two
center pins are at a separate higher
shear line.
When the control key is rotated
counterclockwise, those middle pins
pick up the control sleeve and cause
it to rotate with the plug. That motion
is self limiting. It will only rotate far
enough to pull in the locking lug on
the control sleeve.
The Rule of Three
Because of the control sleeve
design, there will always be a three
depth differential between the control
key and the operating key in the third
and fourth pin positions. If you do
some subtraction, you will see that
the control and operating keys that
were shown in Photograph 4, also
followed that rule.
I had identified the control key
cuts as: 34123, and the operating key
as: 34453. If you subtract three from
the third and fourth cuts on an
operating key for a Medeco I-Core,
you will know what the control key
cuts should be in those same
positions. For our example, four
minus three (third cut) gives us one,
which is the control key cut in that
position. For the fourth cut, five
minus three gives us two, which is
the fourth cut on the control key.
This is very useful information for
the locksmith who needs to service a
Medeco I-Core cylinder. If the
customer has lost or misplaced the
control key, you can use the
operating key to determine the
proper cuts and create a new control
key.
Consequences to the Rule of
Three
There are certain unavoidable
consequences to the design of the
control sleeve and its rule of three.
First of all, certain cut combinations
cannot be used in the third and
fourth pin chambers. Because the
control key cuts must be three
depths shallower to engage and
operate the control sleeve, there is a
limit to how shallow a cut can be
which is used in those two pin
positions on the operating key.
Let’s test the limits. We will see
what happens when we attempt to go
beyond the recommended boun-
daries for keying and pinning the
Medeco interchangeable core. This
will apply only to the pin chambers
contained within the control sleeve.
For your operating key, I’ll suppose
that you want to make a #3 cut in the
third position and a #2 cut in the
fourth position. I’ll apply the rule of
three and subtract three from both
numbers. When I subtract three from
three (third cut) I end up with zero,
and subtracting three from two
(fourth cut) leaves negative one. We
know that the shallowest cut on a
Medeco key is a #1 cut. It seems that
it is physically impossible to make a
control key to work with a Medeco I-
Core coded in such a way.
Here are the numbers that you
must remember when picking key
cuts in the third and fourth positions
for operating or control keys. The
operating key cuts can be: 4, 5 or 6. If
you subtract three from any of those
numbers, you will always come up
with a useable Medeco depth. For the
control key, the cuts in the third and
fourth positions will be: 1, 2, or 3.
When master pinning in those pin
chambers, you’ve got a few other
things to watch out for. Although
change keys can have depths
shallower than #4 in those two
positions, the top master key (TMK)
must follow the same rule as an
operating key for a non-master keyed
cylinder. The reason is that the
control key will be based on the TMK
cuts, since the TMK should operate
all cores in the master key system.
There are a few other important
restrictions. Normally with a master
key system, you always avoid using
any of the master key cuts on a
20 • The National Locksmith
Illustration 2. A side cutaway
views of the Medeco I-Core to
illustrate how the control sleeve
works.
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