Simple metrology of gear

1. A.D.Patel Institute of
Technology
KINEMATICS
OF
MACHINES
1. Sagar Dharmani. 120010119009
2.Swapnil Sharma. 120010119067
3.Teerth Thummar. 120010119109
4.Nirmal Parikh. 120010119121

2. Gear Metrology

3. Sr.
No.
Topic
1 Introduction
2 Gear Terminology
3 Tooth Thickness Measurement Methods
4 Profile Checking
5 Bibliography

4. Introduction
“A gear is a toothed with the teeth cut on the
periphery of a cylinder or a cone commonly used to
transmit power or motion, from one shaft to another,
without sleep”
 A gear or cogwheel is a rotating machine part having
cut teeth, or cogs, which mesh with another toothed
part in order to transmit torque, in most cases with teeth
on the one gear of identical shape, and often also with
that shape (or at least width) on the other gear.
 Two or more gears working in tandem are called a
transmission and can produce a mechanical
advantage through a gear ratio and thus may be
considered a simple machine.
 Geared devices can change the speed, torque, and
direction of a power source. The most common
situation is for a gear to mesh with another gear;
however, a gear can also mesh with a non-rotating
toothed part, called a rack, thereby producing
translation instead of rotation.
 The gears in a transmission are analogous to the
wheels in a pulley. An advantage of gears is that the
teeth of a gear prevent slipping.

5. Gear Terminology

6. Root Diameter
Diameter of root circle.
Pitch Diameter
Diameter of imaginary pitch
specifying addendum and
dedendum.
Outside Diameter
Diameter of
addendum(outside) circle.
Addendum
Radial distance from pitch to
top of tooth.
Dedendum
Radial distance from pitch to
bottom of tooth.

7. Tooth Thickness
Thickness of a tooth along the
pitch circle.
Clearance
Distance between top of a
tooth and bottom of matting
space.
Working Depth
Distance a tooth projects into
matting space.
Whole Depth
Total height of the tooth.
Circular Pitch
Distance on pitch circle from a
point on one tooth to
corresponding point on the
adjacent tooth.

8. Tooth Thickness Measurement
Methods

There are direct and indirect methods for
measuring tooth thickness. In general, there are
two methods:
1. Chordal Thickness Measurement
2. Span Measurement

9. 1. Chordal Thickness Measurement
This method employs a tooth caliper that is
referenced from the gear's outside diameter.
Thickness is measured at the pitch circle.as shown
in fig

10. 2. Span Measurement
The distance between numbers of teeth.
Span measurement of teeth, Sm, is a measure over
a number of teeth, Zm, made by means of a
special tooth thickness micrometer.
The value measured is the sum of normal circular
tooth thickness on the base circle Sbn and normal
pitch, Pen (Zm – 1).

11. Profile Checking
The portion of tooth flank between outside circle
and the specified from circle of diameter
approximately equal to pitch circle diameter minus
twice the dedendum is called Profile Checking.
The following methods are used to check the
involute profile of gears.
i. Optical projection method
ii. Using involute measuring machine
iii. Tooth displacement method
iv. Computer Controlled Probe

12. 1. Optical projection method
In this method an optical comparator and profile
projector are used to magnify the profile of the
gear under test and then it is compared with the
master profile as shown in fig. 2A.
This method is quick and suitable for checking the
profile of small thin instrument gears.

13. 2. Using of involute measurement
machine
This machine is designed for checking the involute
profiles of the gears.
If a straight edge is rolled around a base circle
without slipping, stylus of the dial gauges are
attached to the straight edge would traverse a true
involute
This method is mainly used for large sized gears.

14. 3. Tooth displacement method
This method is used for large and when special
purpose involute measuring equipment is not
available.
In this method the gear is rotated through small
angular increments and the readings of the
vertical measuring or the height gauges are
compared with the theoretically calculated values
at a 5-10 places along the tooth flank.
This method is very time consuming but is best
suited for calibration of master involute, so it is
used only for very precision components.

15. 4. Computer Controlled Probe
Scanning Method
The measurements are taken with a computer
controlled probe scanning at a constant rate with
a constant force from the root of the tooth to its tip.
After the data is collected for all the teeth, it is
mathematically evaluated to determine profile
from error and concentricity as well as base circle
shrinkage error and actual tooth thickness.

16. Bibliography
http://books.google.co.in/books
http://www.docstoc.com/docs/113210028/
GEAR-METROLOGY
http://www.scribd.com/doc/54503965/Me
trology-Gear-Measurement
http://gearmeasurement.net/