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                            Chicago School of Watchmaking Home Study Course
                        
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Page 1

Chicago School of Watchmaking Home Study Course

The Chicago School of Watchmaking

Home Study Course



Master Watchmaking

A Modern, Complete, Practical Course

Lesson 22

PRINCIPLES OF THE LEVER ESCAPEMENT

Chicago School of Watchmaking Founded 1908 by Thomas B. Sweazy




HOW THE ESCAPEMENT WORKS

The escapement has three main parts: The escape wheel,
the pallet assembly, and the rollers. Power from the
mainspring turns the escape wheel clockwise while the
rotation of the balance Wheel turns the rollers, which are
on the balance staff.

In Fig. A, the escape wheel is locked on the receiving
stone. Nothing is moving except the balance, which is
turning counter-clock wise, as indicated by the arrow.
(The balance and hairspring are not shown because they
would block the View of the fork and roller action.) The
roller jewel is approaching the fork.

In Fig. B, the roller jewel has entered the fork slot and

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Chicago School of Watchmaking Home Study Course

struck its far side, putting the fork lever into motion.
This pulls up one arm of the pallet and also causes the
escape Wheel to back up slightly or recoil. The pallet
stone slides on the corner of the escape wheel tooth until
the corner of the tooth passes the corner of the escape
wheel. This releases the escape wheel.

Power from the mainspring now drives the freed escape
wheel clockwise. As it turns, the tooth of the escape
wheel slides on the impulse face of the pallet stone and
kicks it up out of the way, driving the pallet arm higher,
Fig. C. This speeds the movement of the fork compared
to the speed of the roller jewel. The fork strikes the jewel
from behind and gives it a shove. This gives the impulse
to the balance which continues to turn, causing the
hairspring to contract or wind up.

As the escape wheel tooth slides off the impulse face of
the pallet stone, the wheel turns freely for a short
distance. This phase is known as the drop. When the
impulse forces up the receiving arm of the pallet, it also
forces the discharging arm of the pallet to move down
and halt another tooth on the discharging stone. This
phase is called lock, Fig. D.

After halting the tooth, a force called draw causes the
stone to move further into the wheel. This movement
after the lock is called slide, Fig E.

With the escape wheel locked, the roller jewel , carried
by the balance, swings free of the fork slot and continues
to move counter-clockwise until it is stopped by the
contracting hairspring. At this point it reverses direction
and the same sequence begins again going the other way.





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Chicago School of Watchmaking Home Study Course

divergence
is in the
wrong
direction;
at A, where
it is in
proper
position,
the
divergence
natural.

There is
another
result from
moving a
pallet stone
which
must not
be
overlooked.
It changes
the extent
of the arc
of
vibration
of the
pallets. In
other
words- it
changes
the lift.

The term
lift is
applied to
the thrust
given to
the pallets
by an
escape

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Chicago School of Watchmaking Home Study Course

tooth. In
the lift the
pallets,
swing on
their own
center and
the extent
of that
swing is
called the
arc of
vibration.
It has been
explained
that the
circular
impulse is
measured
from the
center of
the escape
wheel and
is divided
between an
escape
tooth and a
pallet
stone. The
lift is
measured
from the
pallet stone
and is also
divided
between an
escape
tooth and a
pallet
stone.

Figure 22-
10 shows

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Chicago School of Watchmaking Home Study Course

You can test the draw with the balance out of the movement by pushing the fork away from the banking with a pointed pegwood but
not to the point of unlocking. If you now lift the pegwood and release the fork, it should return promptly to the banking pin.

When the balance is in the movement, you can test draw by turning the balance wheel so the jewel is outside the fork horns. While it is
in this position, push the fork away from the banking with a pointed piece of pegwood or small broach until the guard dart contacts the
roller. Now take away the pegwood. If draw is present, will at once return to the banking.








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Chicago School of Watchmaking Home Study Course


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