Ever wonder how man-made things are the way they look like? Why does a bridge look exactly like this:

Or why do tables have rounded corners like this:

 

The thing is every feature in a design is properly calculated. Chances are, without the feature that seems to just add style, the object would simply fail to work in a proper manner. Before making anything, the design is first conceived and finalised. Having a properly calculated design and adherence to it while manufacturing the item is equally essential.

But how to get started with "designing something"?

Take any mechanical component for example, A bearing.

Now the first part of the design methodology is to figure out the dimensions that must be found out. If you look at the above picture closely, you might see an inner hole, an outer ring and a thickness. That makes it 3 primary dimensions.

The inner diameter.

The outer diameter

The length (thickness) of the bearing.

The second part is the selection of the material.

Its taken for granted that before the design, all the operating conditions have been given to you. The operating conditions gives a good idea of the stresses subjected to it.

The next reason of stress are the forces acting on it while operation. You have to calculate these forces. Based on these two factors, you can select a relevant material from the design data book. If it is an actual industrial project, then you might take a look at the company catalogue and the materials inventory for material selection.

Third, the check for safety. Having found the stresses and the material, the most important part is factor of safety. Setting a factor of safety depends on the component and the company producing. Some companies may use an FOS of 4–6 (especially gears) while some companies may keep it as much as 28–30 (chains and sprockets).

Set a factor of safety and see if the calculated forces are less than the permissible value. If the latter is more, then it is an unsafe design. Unsafe design troubleshooting employs a lot of methods like:

:- Change of material

:- Change of the dimensions

Addition of extra components similar to the none in question. And more…

If you need a more clear view of design methodology, I suggest you to read

:- Machine Design By R.S Khurmi

:- Design of Machine Elements By V.B Bhandari

These are a few of the many books available.

Hope you got an idea of the approach for component designs!