What is Tolerance ?
Permissible variation in the size (dimension) of a component to suit Functional
Requirements
How to choose Tolerance?
•Cost of Production
•Productivity (Time)
•Availability of Manufacturing Resources
Tolerance Callout
Hole : 25 H7
Shaft : 25 g6
Assembly : 25H7g6
Tolerance Zones – Shaft and Hole
GAUGES
Gauging, done in manufacturing processes, refers to the method by which it is determined
quickly whether or not the dimensions of the checking parts in production, are within their
specified limits.
 It is done with the help of some tools called gauges.
Gauges are the tools which are used for checking the size, shape and relative positions of
various parts but not provided with graduated adjustable members.
Gauges are, therefore, understood to be single-size fixed-type measuring tools.
Classifications of Gauges
(a) Based on the standard and limit
• Standard gauges
• Limit gauges or “go” and “not go” gauges
(b) Based on the consistency in manufacturing and inspection
• Working gauges --Working gauges are those used at the bench or machine in gauging the work as it being made.
• Inspection gauges --These gauges are used by the inspection personnel to inspect manufactured parts when finished.
• Reference or master gauges --These are also called master gauges. These are used only for checking the size or condition of
other gauges and represent as exactly as possible the physical dimensions of the product.
(c) Depending on the elements to be checked
• Gauges for checking holes
• Gauges for checking shafts
• Gauges for checking tapers
• Gauges for checking threads
• Gauges for checking forms
(d) According to the shape or purpose for which each is used
• Plug
• Ring
• Snap
• Taper
• Thread
• Form
• Thickness
Go-NoGo Limit Gages
Objective
•Check if the part size is within the Upper and Lower size Limits
•Go gage should always go (into the part).
•NoGo gage should NOT go.
•Go gage should check both part Form and Dimension.
Taylor’s Principle for Gage Design
Go gage size corresponds to the Maximum Material Condition (MMC) of the Part.
• Upper size limit for Shaft
• Lower size limit for Hole