MIT Guide to Lock Picking by Ted the Tool - HTML preview

Chapter

9

will

use

this

mo del

to

explain

complicated

mechanical

defects.

The

" atland"

mo del

of

a

lo

c

k

is

shown

in

Figure

3.1.

This

is

not

a

cross

section

of

a

real

lo ck.

It

is

a

cross

section

of

a

very

simple

kind

of

lo ck.

The

purp

ose

of

this

lo

c

k

is

to

keep

tw

o

plates

of

metal

from

sliding

ov

er

eac

h

other

unless

the

prop

er

key

is

presen

t.

The

lo ck

is

constructed

by

placing

the

tw

o

plates

ov

er

each

other

and

drilling

holes

whic

h

pass

through

b

oth

plates.

The

gure

sho

ws

a

t

w

o

hole

lo

c

k.

Two

pins

are

placed

in

eac

h

hole

such

that

the

gap

b etw

een

the

pins

do

es

not

line

up

with

the

gap

b etw

een

the

plates.

The

b ottom

pin

is

called

the

key

pin

b ecause

it

touches

the

k

ey

.

The

top

pin

is

called

the

driver

pin.

Often

the

driver

and

k

ey

pins

are

just

called

the

driver

and

the

pin.

A

protrusion

on

the

underside

of

the

b ottom

plate

keeps

the

pins

from

falling

out,

and

a

spring

ab

o

v

e

the

top

plate

pushes

do

wn

on

the

driver

pin.

If

the

key

is

absen

t,

the

plates

cannot

slide

o

v

er

eac

h

other

b

ecause

the

driv

er

pins

pass

through

b oth

plates.

The

correct

key

lifts

the

pin

pairs

to

align

the

gap

b etw

een

the

pins

with

the

gap

b etw

een

the

plates.

See

Figure

3.3.

That

is,

the

key

lifts

the

key

pin

un

til

its

top

reaches

the

lo

c

k's

sheer

line.

In

this

conguration,

the

plates

can

slide

past

eac

h

other.

Figure

3.3

also

illustrates

one

of

the

imp

ortan

t

features

of

real

lo cks.

There

is

alwa

ys

a

sliding

allow

ance.

That

is,

any

parts

whic

h

slide

past

eac

h

other

must

b e

separated

b

y

a

gap.

The

gap

b etw

een

the

top

and

b ottom

plates

allows

a

range

of

keys

to

op en

the

lo ck.

Notice

that

the

righ

t

k

ey

pin

in

Figure

3.3

is

not

raised

as

high

as

the

left

pin,

y

et

the

lo

c

k

will

still

op en.

7

Figure

3.1:

Flatland

mo del

of

a

lo ck

Figure

3.2:

(a)

Flatland

k

ey

raises

pins

Figure

3.3:

(b)

Prop

er

key

allo

ws

plates

to

slide

8