Dimensional Tolerance of GD&T

History of our GD&T starts before the second world war during 1939-1945.

at the end of this lesson learner will able to understand the followings

• Migration of traditional way of measurement to our latest GD&T.

  
  

• X-Y square tolerance zone.

• Deficiency and problems with these traditional X-Y square tolerance zones.

• True position.

• Emerging of Circular tolerance zone.

• Benefits and importance of circular tolerance zone

  
  

• Mr.Stanley Parker's first GD&T  concept.

  
  

  These X-Y Square tolerance zone and Circular tolerance zone are explained with small bolt and nut assembly.

GD&T history continues..

at the end of this lesson readers will come to know

•      BSI – Standards.

•      SAE – Standards.

•      ANSI / ASME standards.

•      ASME Y-14.5 -2009 for 21st century.

Definition of GD&T.

GD&T frame and its characteristics.

At the end of this lesson learners will able to acquire knowledge on

Dimensional tolerance and Geometrical tolerance.

System of tolerance specifications

• Bilateral.

• Unilateral.

• Limits Method.

Methods to read and write the dimensions in Millimetre and Micrometer.

Basic terminologies of dimensional tolerance

• Basic size & Actual size with practical design calculations.

• Limits maximum & Minimum with pictorial explanation.

Basic terminologies of dimensional tolerance continued...

Allowance and explanation.

• Positive allowance

• Negative allowance

  
  

  With graphical aided explanation.

  
  

At the end of this lesson learners will able to find Basic Dimensional tolerance data by arithmetic calculations

• Basic size

• Limit

• Upper and lower limits

• Upper and lower size

• Tolerance

Exercises for practice.

Practice exercises questions and answers to find basic Dimensional Tolerance data.

Features

• It is one of the fundamental interview question.

• All the answer results are in millimetre and micrometer.

• Two examples based on unilateral tolerance.

• Two examples based on bilateral tolerance.

First half Part :

At the end of this lesson learners will able to acquire knowledge on

How to apply Dimensional Tolerance and Geometrical Tolerance on AutoCAD drawing using the following commands.

• Dimlinear

• Ddim

• Tolerance

• Qleader

Second half Part :

Discussion on the following two important question of tolerance and finding the answer with enough evidence

on what basis the Tolerance values are found?

How much will the Tolerance values be?

What are the effects of clearance between the parts becoming more and less?

with graphical aided explanation.

Introduction to fits.

At the end of this Lesson the learners will have commendable knowledge on Fits and it types.

The objective of the lesson is achieved as follows

Definition with explanation each type of fits are explained with animated examples.

1. Clearance fits

• Slide fits

• Running fits

2. Interference Fits

• Force fits

• Tight Fits

• Shrink Fits

3. Transition fits

• Push Fits

• Wringing Fits

And engineering drawing representation of each fits with descriptions.

Goal of this lesson is to explain the universal standard of the system of fits with graphical aids.

Hole basis system and Shaft basis system of fits are explained with animated videos and representation of the same in engineering drawing.

Also clarifies the following questions and topics.

Why Hole basis system is preferred?

Challenges of Shaft basis system

Best use of Hole basis system in the view of metrology.

At the end of this lesson learns will able to calculate & find the type of fit and the same is achieved by addressing the following

Basic size / Zero line / References in Shaft Basis System & Hole Basis System

And derived empirical relations are used to calculate the following on the base of Hole Basis System.

1. Clearance fit

How to calculate Maximum and Minimum allowance / clearance?

2. Interference fit

How to calculate Maximum and Minimum negative allowance / Interference?

3. Transition fit

How to calculate Maximum clearance and Maximum Interference?

Features:

• 3 problems are explained.

• 7 exercises are given for practice.

Numerical calculations were discussed to find the type of fit for 7 practical exercises.

Features:

• Unilateral and bilateral combination of tolerances were discussed

• Wrong question for the right reasons.

• Clearance fit 3 questions , transition and interference fit 2 questions each were explained with engineering representation of each fit.

Calculation of finding fits from given Limit dimensions is discussed in this lesson.

Critical thinking is enhanced with various range limit dimensions for finding the fits.

It is a another method of finding the limits and fits.

Exclusive three different variety of questions with critical data were discussed and solved for the same.

Aim of this lesson to make understand the designation of fit

The first objective is to discuss the system of tolerance like

Unilateral & Bilateral tolerances.

Both are explained with live examples and its uses.

The second objective is to declare the rules to be followed in dimensional tolerance.

The final objective of the lesson is to deal with description and meaning of designation of the hole and shaft tolerance on engineering drawing and as well assembly drawing.

Introduction of GD&T of hole basis and shaft basis table for validation.

Fundamental deviations of Hole and Shaft is explained with chart and table in this lesson.

The following topics are explained with graphical aid and its charts

• Assumptions and reasons of fundamental deviation.

• Designation of fundamental deviation of Hole / Shaft.

• Fundamental deviation of hole:

            Basic size of hole.

            Range of each hole zone and its magnitude.

            Clearance,transition & interference fit hole zone.

• Fundamental deviation of Shaft:

           Basic size of shaft.

           Range of each shaft zone and its magnitude.

           Clearance,transition & interference fit shaft zone.

At the end of this lesson learners will be able to understand the standard International tolerance grade and calculate the minimum and maximum limits of respective shaft and hole.

1. Discussing the Fundamental deviation of shaft – Hole Basis system (with graph and table)

          +ve region of shaft deviation – Lower deviation

          -ve region of shaft deviation – Upper deviation

  2. Discussing the Fundamental deviation of Hole – Shaft Basis system (with graph and table)

         +ve region of Hole deviation – Lower deviation

         -ve region of Hole deviation – Upper deviation

3. Calculation to find the minimum and maximum limit of the hole and shaft of desired combination of fit using

     Table of Fundamental deviation of Hole/Shaft and

     Table of IT grade tolerance value

     Finally the answers were validated with GD&T Table.

4. Four different practice exercises were given to find the type of fit from the respective Hole & shaft combination.

In this lesson 4 critical exercises were discussed with aid of Hole basis system graph,

Each exercise is explained to find the limits of Hole & Shaft from the

Table of Fundamental deviation of Hole/Shaft and

Table of IT grade tolerance values.

And all the answers were cross checked with the GD & T table.

The entire lesson explains the finding of Deviations and Tolerances by Formula.

OR

How the GD&T table values are evaluated and tabulated?

Finding the

• Fundamental deviation,

• Tolerance and limit size of hole and shaft,

• Calculation of standard fit.

by empirical formula using the following standard steps

1. Mean diameter.

• IS recommended diameter steps.

2. IT grade value.

• Table of IT grade.

3. Fundamental deviation of Hole / Shaft.

• Table of Fundamental deviation.