Tech Tips:Designing Sheet Metal Notches and Tabs

Notches and tabs are two of the most common features found in precision sheet metal parts, and it’s easy to see why. These features give you space so you can get tools into an area. Also, they help avoid space conflicts between parts or features, especially when incorporating parts together in an assembly.

Dimensional Rules for Notches

Here are two easy-to-apply design criteria for notches: First, the width should be at least.040 in. (1.016 mm) or the material thickness, whichever is greater. Second, notch depth should be no deeper than 5x its width, depending on its purpose. For instance, if a notch is a standalone feature and isn’t part of a series of successive notches (see notch 3 in the figure below), then the depth is not limited.

Dimensional Rules for Tabs

Tabs (or fingers) are successive, tightly spaced, protruding strips of metal. #2: This notch does not extend past the perimeter. #3: This is a slot. The lack of successive strips means there are fewer rules governing their use.

One fundamental rule is that tabs (and notches) should be at least twice the material thickness of your sheet metal or .125 in. (3.175mm) wide, whichever is greater, and no more than 5x its width. Although there are exceptions to these guidelines, if you can maintain these basic dimensions, you’re ensuring strong tabs and structurally sound notches. When tabs exceed 5 times their width, their strength is sacrificed, and you may end up with unwanted flexibility and deformation.

Why Should I Use Notches or Tabs?

These features can be useful for locating parts in an assembly, much like slots can. A tab on an interior part simply slides into a notch on a chassis or box. Doing that can help more precisely locate the part before riveting or even welding in places where location and strength are more important than aesthetics. Tabs can mate with slots to align for welding or create a weld-free enclosure that is easy to assemble. Support your fabricator by designing these features into your part to make processing and assembly a breeze. Doing what you can on the front end will help ensure we can get you a quality part on the back end. Keep in mind that if you are designing notches and tabs that mate with each other, longer features may be challenging to mate together, particularly if numerous notches and tabs are used. Consider using the shortest possible tabs to achieve your design. This will go far to support assembly/welding operations.

Strategies for Limited Space in Sheet Metal Assemblies

With assemblies becoming smaller in size, the need to notch flanges near screws, nuts, or electronics has become almost inevitable. Still, it’s important to balance the need for space with the structural strength of the part. Following the basic criteria listed above as much as possible will ensure strength and structural integrity.

Wide, shallow notches are a great way to ensure a quality cut and a strong feature.

In some situations, you can use bent tabs in tandem with spot welding or riveting to place a part without the need for a longer flange or fillet welding. Bear in mind that when mating something against a formed tab, the mating part will not be able to occupy the same space as the bend radius. Plan for the mating part to leave space for the bend radius of the formed tabs. These bent tabs would still need to follow the general rule that the tab’s length should exceed 4x material thickness for easy forming.

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