Sheet Metal Corner Relief Size

When considering sheet metal thickness a single sheet with punches holes is a good rule of thumb.

Sheet metal corner relief size.

When sheet metal makes a transition from a bend to a flat surface or to another bend it tends to rip and tear. This option is straight forward. For a 3 width ratio when the part is 1 mm in thickness the width of the slot will be 3 mm. Assume the thickness is 1 mm a ratio to thickness equals to 4 will create a 4 mm per side square relief fig 5 for the obround relief the ratio to thickness options works in a similar manner.

If you use the close 2 bend corner tool you can take the two corner types shown above and they will look like the closed corner shown below with the flat pattern to the right. To eliminate this a bend relief is added so the edge of the sheet metal is perpendicular to the bend.