How To Show Fillets And Rounds In Technical Drawings?

Technical drawing documentations are very important in manufacturing engineering. In the r&d department, technical drawing documentation is prepared for the manufacturing site. Technicians and engineers read these technical sheets to understand which kinds of parts and shapes will be produced with which kinds of processes. 

There are lots of kinds of information in technical drawing sheets such as surface roughness, manufacturing process types, scales, information about assembly of the part, shape, and geometry of the part. All of these factors are indicated on technical drawings with standardizations. So, shapes and geometric features are indicated as standards on technical drawings. 

Here we will show how to show fillet and round geometries on technical documentation in terms of standard presentations. 

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What Are Rounds And Fillets On Mechanical Parts?

Rounds and fillets are commonly used geometrical entities in mechanical part design. They have distinct reasons to be used as geometric entities in mechanical designs. 

Rounds are the softening of convex edges of geometries by adding a radius value. So in a mechanical part design, probably there are no sharp edges, all the edges are rounded because of some reason. 

Also, fillets are the softening geometric entities on concave edges. You can not see a sharp concave edge on a mechanically designed entity. These sharp and concave edges are also rounded to specific radii.

In the production of parts, there are various manufacturing processes are used. The most common manufacturing processes are casting and forging operations. In these operations, it is very hard to produce sharp edges and corners because of the molds and material characteristics. And sharp edges and corners decrease the mechanical strength of the parts. Because they act as stress raisers. 

How To Show Fillets And Rounds On Technical Drawings?

Actually, it is very easy to show fillets and rounds on technical drawings. They are shown as small swirls on different views of a part. Check the examples below to understand the principles; 

(Image Source: Frederick E. Giesecke_ Alva E Mitchell_ Henry C. Spencer_ Ivan L Hill_ John Thomas Dygdon_ James E. Novak_ R O Loving_ Shawna Lockhart_ Cindy Johnson – Technical Drawing with Engineering Graphics)

If you take a look at the front view of this drawing, the rounds of the corners are shown as very small swirls. 

(Image Source: Frederick E. Giesecke_ Alva E Mitchell_ Henry C. Spencer_ Ivan L Hill_ John Thomas Dygdon_ James E. Novak_ R O Loving_ Shawna Lockhart_ Cindy Johnson – Technical Drawing with Engineering Graphics)

Also in this example, you can completely understand how to show both fillets and rounds on the same part. You can directly show the fillets and rounds effects on the geometry of part in your technical drawing! 

How To Show Dimensions Of Fillets On Technical Drawings?

(Image Source:

To show the dimensions of fillets and rounds is a very important thing. But it is very easy. You can see an example below to show how to show the dimensions of fillets and rounds. You just need to put ‘R’ just before the radius dimension of fillets and rounds. 

If your geometry has symmetry; for example, your geometry symmetrically has 4 same fillets. You can show the dimensions of all these symmetrical fillets on one fillet or round geometry like this; 4XR10. This means these 4 symmetrical fillets have 10 units of radii. 


This is very easy like this to show the fillets and rounds on technical drawings with their dimensions.

Do not forget to leave your comments and questions below about the fillets and rounds in technical drawings!


One response to “How To Show Fillets And Rounds In Technical Drawings?”

  1. Přemysl B: Avatar
    Přemysl B:

    Dear sir or madamme,
    I am Czech and therefore sometimes do not understand the exact meaning of english/american expresions.

    Fillet ! Can you please explain me weather it is inner wall radius or inner bottom radius? And how do you distinguish them in english?

    Thank you

    Your sincerely PB

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