397 OF ENGINEERING FOBMULÆ.
Construction of the Teeth of Wheels.
EPICYCLOIDAL TEETH.
In making a set of wheels, the teeth of all
wheels of the same pitch that may be required
to work together should be generated by the samo
rolling circle.
The best diameter of’the rolling circle for any
pitch = pitch X 2'22, unless any wheel in tlio
set should have less than fourteen teeth. No
wheel should have less than fourteen teeth, but if
it is unavoidable, in that case the diameter of the
rolling circle may be determined by the following
formula :
D — Diameter of rolling circle.
P = Pitch of teeth.
N = Number of teeth in the smallest wheel of
the set.
_ NP
~ G-3 ‘ .
The diameter of tlie rolling circle must in no
case exceed the radius of the least pitch circle in
the set. The plan of making the rolling circle
equal to the pitch circle is incorrect.
Nature of Cceves of Teeth.
Curve of Root. Curve of Point.
In a straight rack . • •. Cycloidal • • • • Cycloidal,
In a wheel ........Hypocycloidal .. Epicycloidal.
. In an internal segment.. Épicycloidal.. .. Hypocycloidal.
In the workshop the curves of the teeth are
struck out by rolling the template of the genera-
ting or rolling circle on a template corresponding
with the pitch line. A scriber or pencil on the
periphery of the generating circle maxkiug out
the required curve.