2. Sanjivani Rural Education Societyβs
Sanjivani College of Engineering, Kopargaon-423603
( An Autonomous Institute Affiliated to Savitribai Phule Pune University, Pune)
NAAC βAβ Grade Accredited, ISO 9001:2015 Certified
Subject :- Theory of Machines II
T.E. Mechanical (302043)
Unit 2
2.3 WORM AND WORM WHEEL
By
Prof. K. N. Wakchaure(Asst Professor)
Department of Mechanical Engineering
Sanjivani College of Engineering
(An Autonomous Institute)
Kopargaon, Maharashtra
Email: wakchaurekiranmech@Sanjivani.org.in Mobile:- +91-7588025393
3. WORM AND WORM GEAR
ο§ Worm gears are used when large gear reductions are needed. It is common for worm gears to have
reductions of 20:1, and even up to 300:1 or greater
ο§ Many worm gears have an interesting property that no other gear set has: the worm can easily turn
the gear, but the gear cannot turn the worm
ο§ Worm gears are used widely in material handling and transportation machinery, machine
tools, automobiles etc
3Subject :- Theory of Machines II
Worm Wheel
Worm
4. Axis of Rotation
Transverse axis
Thread orientation
πΏ
Ξ±1
πΏ= lead Angle
Ξ±1= Angle made by the Worm thread
with axis of rotation
Ξ±1 + πΏ = 90Β°
WORM AND WORM GEAR
5. β’ Axial Pitch (P) of a worm is a distance measured along the pitch line of the gear.
β’ It can be determined by measuring the distance between any corresponding points of
adjacent threads parallel to the axis.
β’ It is note that the axial pitch of a worm is equal to Circular Pitch (Pc) of the mating worm
gear.
NOMENCLATURE
6. Lead ( L ) is the linear distance through which a point on a thread moves ahead in one revolution of
the worm.
For single start threads, lead is equal to the axial pitch. Therefore, lead can be calculated as the
product of axial pitch and number of starts.
L=n*P
P=axial Pitch
n= no. of Starts
NOMENCLATURE
For Single Start: L=P
For Double Start: L=2*P
For Triple StartL =3*P
7. ο§ tan(πΏ)=
πΏ
Ξ .d
ο§ L= n*P
ο§ n= No. of Start
ο§ P= Pitch
ο§ πΏ= π‘ππβ1
(
πΏ
Ξ .d
)
Ξ .d
L
πΏ
Lead Angle (πΏ ) is the angle between the tangent to the tread helix on the pitch cylinder and
the plane normal to the axis of the worm.
β’ If one complete turn of a worm is imagined to be unwound from the body of the worm, it
will from an inclined plane whose base is equal to the pitch circumference of the worm and
altitude is equal to lead of the worm, as shown below.
β’ In addition, the lead angle is an important factor in determining the efficiency of a worm
and worm gear set. Therefore, the efficiency increase as the lead angle increases.
NOMENCLATURE