Engineering drawings

INTRODUCTION

A tool which is used to communicate the design and manufacturing information of a part is called as the engineering drawings.
Dimensions and tolerances are a very important aspect of engineering drawings.
Dimensions and tolerances help manufacturing officials to understand the requirement and build the product accordingly.

What Is An Engineering Drawing?

An engineering drawing is a document that gives a brief information of the part.
This information consists of numbers, symbols, words and pictures.
Engineering drawing information includes:

  1. Geometry (shape, size and form of the part).
  2. Critical functional relationship.
  3. Tolerances.
  4. Material, heat treat and surface coatings.
  5. Part documentation information.

For many decades, engineering drawings were created by manual methods.
These methods mainly included drafting boards, T-squares, compasses, triangles, etc.
The creation of drawing initially took place on paper, linen, mylar and some other materials.

Nowadays engineering drawings are produced electronically.
The use of computers in modern age has helped designers to create the drawings as well.
Copies are made with the help of printers.
Whether the engineering drawings are manual or electronic computer files, they serve the same purpose of communicating the part information from a designer to the user.

Engineering drawings are a type of communicating tools.
They are a form of legal documents.
Engineering drawings are capable of defining all the specifications of the parts.
All the specifications mentioned in the drawings are measurable.
If the engineering drawings are not created precisely they tend to impact the costs.

CONSEQUENCES OF POOR ENGINEERING DRAWINGS

The main intention of the drawings should be to provide accurate and precise information and most importantly it should be correct.
The cost associated with a drawing error is too high.

Hope you all are with me and if in case any doubt please utilize the comments section!

Now we’ll take a example of a small manufacturing firm to understand the topic in a better way.

Drawing error
Increment of error cost in organisation

The fig. shows typical cost incurred to the firm due to all the errors.
The drawing errors which are found out in the department itself during quality check would cost few dollars.
This cost would include just the time required to correct the errors which would be around 1-10 dollars.
But if this error is missed by the design department and is captured in the model shop then the cost of this error would be around several hundred of dollars.
The increase in cost is due to the addition of material loss, time of machine and the precious time of machinist with the additional efforts from design team as well.

Now we’ll consider the worst case scenario in which the part goes for production.
The error cost in this situation gets summed up very quickly.
Paper work cost for fixing the drawing error is too much and would be around several thousand dollars.
It also includes gaging costs, tooling costs and scraping costs which can easily increase the total to hundreds of thousand dollars.

If the parts are developed with errors and shipped to the customer then the cost of this loss would be much greater.
For example if the part is rejected by the customer and is recalled then the firm would be easily get a loss of few million of dollars.
Lawsuit is the final stage and the cost imposed on the organisation for defective parts would depend on the application of the parts.

What are the ways in which the drawing errors cost the organisation?

The 4 ways in which drawing errors cost the organisation are as follows:

  1. Money.
  2. Time.
  3. Material.
  4. Unhappy customers.

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