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Read basic mechanical drawings

Large Wreath

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WE Development

Large Wreath

Content written by:

WE Development

Last Updated:

9 June 2021 at 2:51:19 am

Image by Daniel Mirlea
Job Process

Whenever you need to mount or assemble something, you need to rely on mechanical drawings!

Because we are dealing with basics, here are 5 tips to take note when interpreting a mechanical drawing!

1) Part Number

2) Metrics

3) Mounting Points

4) Views

5) Tolerances

1) Part Number

Part number gives us the certainty that we are working on the correct part. This is also the key information used to search online for part drawings if you are purchasing or working with components from a supplier. 

2) SI Units

If you are working with US products, the parts will most likely be in Inches. Otherwise, milimeters is quite common. 

Knowing 25.4mm is equivalent to 1'' (1 inch) is the minimum basics you need to have. You also need to be mindful that for holes, the type of threading and depths follows the SI units as well, unless specified seperately.

For example, you need to understand what is 5/16 hole. In this case, is a 7.9mm diameter hole acquired by having 5/16 multiplied by 25.4 (conversion from inch to mm). 

3) Mounting Points

At the basic level, we are often concern about how we can mount a component to another. Hence, you need to focus areas in the drawing that have the information on mounting points. It will be good you can refer to pictures or the actual component to verify that the holes are indeed mounting points you could use.

To help you identify if the hole is a mounting point, you can look for holes with labels start with "M" which stands for Metrics (mm) holes. For example, M8 means the hole is designed for 8mm diameter bolt. M6 means the hole is designed for 6mm diameter bolt.

Also, if you working with inches, for example, 3/8-24 means it is a 3/8'' diameter with 24 threads per inch. Do note that 24 means fine thread while 18 means coarse thread. An example is 5/16-18 means this is a 5/16 diameter bolt with 18 threads per inch which is a coarse thread.

If you like to know more, you may click here to read further! 

4) Views

When finding for dimensions that you need, you must know how to identify views. This includes auxilliary views, detailed views, section views and more which are often labeled in the drawing. Keep a look out for those and identify them effectively.

Also, knowing what is top view, front view, etc. are the ground fundamentals an engineering should know and shall not be elaborated here.

5) Tolerances

Occasionally, you may have to design a simple shaft and that you will be struggling a while due to uncertainty of tolerances. It is important you identify your shaft's application and fitting to decide on the way to go. 

"How do I know if I need to be worried about the tolerances?" Many new engineers will ask. The answer is, if the dimension from the part is 2 decimal places and more (for example 2.565mm, you will have to consider more carefully since this require precise machines such as CNC to cut. This means higher cost. You can do your homework here by reading this article and seek clarification from your supplier.

A further upgrade to your understanding is to learn GD&T (Geometric Dimensioning and Tolerancing) which deals with more precise works that are 2 decimal points and more. 

Do take note that GD&T applications on your drawings that are 1 decimal place or less may not be advisable as this can drive manufacturing cost up due to additional processes. Juggling when to place such tolerance is important to balance between quality and cost. You may further read this article to learn more.

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