interference in gears

1. Sanjivani Rural Education Society’s
Sanjivani College of Engineering, Kopargaon-423603
( An Autonomous Institute Affiliated to Savitribai Phule Pune University, Pune)
NAAC ‘A’ Grade Accredited, ISO 9001:2015 Certified
Subject :- Theory of Machines II
T.E. Mechanical (302043)
Unit 1
1.6 Interference in Gears
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

2. INTERFERENCE
 A little consideration will show, that if the radius of the addendum circle of pinion is
increased to O1N, the point of contact L will move from L to N.
 When this radius is further increased, the point of contact L will be on the inside of base
circle of wheel and not on the involute profile of tooth on wheel.
 The tip of tooth on the pinion will then undercut the tooth on the wheel at the root and
remove part of the involute profile of tooth on the wheel.
 This effect is known as interference, and occurs when the teeth are being cut. In brief, the
phenomenon when the tip of tooth undercuts the root on its mating gear is known as
interference.

3. N
O2
O1
M
K
P
L
G H
ⱷ
ⱷ
ⱷ
rb
r
ra
RA
Rb
R
r
INTERFERENCE
If PL >
PN
If KP > PM
If ra> O1N(ramax)
If RA> O2M
(Ramax)

4. INTERFERENCE
 The points M and N are called interference points.
 Obviously, interference may be avoided if the path of contact does not extend beyond interference points.
 The limiting value of the radius of the addendum circle of the pinion is O1N and of the wheel is O2M.
 we conclude that the interference may only be avoided, if the point of contact between the two teeth is always
on the involute profiles of both the teeth.
 In other words, interference may only be prevented, if the addendum circles of the two mating gears cut the
common tangent to the base circles between the points of tangency.

5. INTERFERENCE

6. MINIMUM NUMBER OF TEETH ON THE PINION IN
ORDER TO AVOID
INTERFERENCE

7. MINIMUM NUMBER OF TEETH ON THE PINION IN ORDER TO AVOID
INTERFERENCE

8. N
O2
O1
M
K
P
L
G H
ⱷ
Ɵ
ⱷ
ⱷ
rb
r
ra
RA
Rb
r
R
MINIMUM NUMBER OF TEETH ON THE PINION IN ORDER TO AVOID
INTERFERENCE

9.  t = Number of teeth on the pinion,,
 T = Number of teeth on the wheel,
 m = Module of the teeth,
 r = Pitch circle radius of pinion = m.t / 2
 G = Gear ratio = T / t = R / r
 φ = Pressure angle or angle of obliquity.
 Let AP.m = Addendum of the pinion, where AP is a fraction by
which the standard addendum of one module for the pinion
should be multiplied in orderto avoid interference.
 From triangle O1NP,
N
O2
O1
M
K
P
L
G H
ⱷ
Ɵ
ⱷ
ⱷ
rb
r
ra
RA
Rb
r
R
MINIMUM NUMBER OF TEETH ON THE PINION IN ORDER TO AVOID
INTERFERENCE

10. Ap
MINIMUM NUMBER OF TEETH ON THE PINION IN ORDER TO AVOID
INTERFERENCE

11. This equation gives the minimum number of teeth required on the pinion
in order to avoid interference.

12. MINIMUM NUMBER OF TEETH ON THE WHEEL IN
ORDER TO AVOID
INTERFERENCE

13. N
O2
O1
M
K
P
L
G H
ⱷ
Ɵ
ⱷ
ⱷ
rb
r
ra
RA
Rb
MINIMUM NUMBER OF TEETH ON THE PINION IN ORDER TO AVOID
INTERFERENCE
 T = Minimum number of teeth required on
the wheel in order to avoid interference,
And
 AW.m = Addendum of the wheel, where AW
is a fraction by which the standard
addendum for the wheel should be
multiplied.
 from triangle O2MP

14.  T = Minimum number of teeth
required on the wheel in order to
avoid interference, And
 AW.m = Addendum of the wheel,
where AW is a fraction by which the
standard addendum for the wheel
should be multiplied.
 from triangle O2MP
MINIMUM NUMBER OF TEETH ON THE PINION IN ORDER TO AVOID
INTERFERENCE

15. MINIMUM NUMBER OF TEETH TO AVOID INTERFERENCE
On pinion
On wheel

16. METHODS TO AVOID INTERFERENCE
1.Use of a larger pressure angle can eliminate interference. Having a larger pressure angle results in a smaller
base circle. As a result, more of the tooth profiles become involute. In this case, the tip of the tooth of one gear
will not have a chance to contact the flank of the other gear on its non-involute portion.
2.Interference can be eliminated by under-cutting of tooth. A portion of teeth below the base circle is cut off.
When teeth are produced by this process, the tip of one tooth of a gear will not contact the non-involute portion
of the tooth of other gear, hence, elimination of interference. However, if the undercutting is pronounced, the
undercut tooth is considerably weakened.
3.Elimination of interference is possible by tooth stubbing. In this process a portion of the tip of the teeth is
removed, thus preventing that portion of the tip of tooth in contacting the non-involute portion of the other
meshing tooth. In this case also, the teeth are weakened.
4.Increasing the number of teeth on the gear can also eliminate the chances of interference. Increasing number
of teeth, keeping the diameter same makes teeth smaller and reduces the tendency to interfere
5.Increasing slightly the center distance between the meshing gears would also eliminate interference.

17. t = Minimum number of teeth on the pinion,
r = Pitch circle radius of the pinion =
r= m.t / 2, and
φ= Pressure angle or angle of obliquity, and
AR.m = Addendum for rack, where AR is the fraction by which
the standard
addendum of one module for the rack is to be multiplied.
MINIMUM NUMBER OF TEETH ON A
PINION FOR INVOLUTE RACK IN
ORDER TO
AVOID INTERFERENCE

18. MINIMUM NUMBER OF TEETH ON A PINION FOR
INVOLUTE RACK IN ORDER TO
AVOID INTERFERENCE
L
P
O
φ
φ
H
r

21. 21PROF. K N WAKCHAURE
Subject :- Theory of Machines II