Total Fabrication


How do we determine vee block size?

Vee blocks

A vee block - also known as a female die - is used in combination with a top blade or knife, to bend metal plate.

A knife and vee block used for pressing small radii and angle bends. An acute angle knife and vee block used for pressing acute angles in sheet metal.          A radius knife and vee block used for pressing large radii and angle bends


The figure below shows a multiple vee block.

Multiple vee block


Vee blocks come in various lengths. The most common is a full length that matches the length of the press brake bed.

When pressing a conical shape you must select the vee block size and length to suit the material thickness and length of the object you are forming.

Selecting a suitable vee block opening

Two measurements are needed for a pressing operation

Die showing vee block width and bend radius


The vee block width and bend radius can be calculated but are usually found by referring to a chart on the machine or a data sheet provided by the manufacturer.


Calculating the vee block width

If no pressing guide is available, the minimum width (W) of the vee block opening for pressing mild steel is found using this formula:

W = 8 x thickness of plate

Other types of metals will require a wider vee opening.

Example 1

Using 5mm plate

W = 8 x thickness
    = 8 x 5
    = 40mm

You can use a narrower vee opening for pressing a conical shape but more tonnage per linear metre is required. This could cause the material to fracture along the outside of the bend.

A larger die opening will create a larger bend radius.

Example 2

Bending to 90 degrees

Using mild steel and a vee opening of 40mm you would need 47.8 tonnage whereas with a vee opening of 25mm you would need a tonnage of 68.4.

Therefore when pressing a conical shape, the size of the vee block opening will depend on the capability of the press brake you are using.


Recommended vee opening for stainless steel, aluminium and bisalloy is 12 x the material thickness.

Calculating the bend radius

Calculating the bend radius


The minimum bend radius is calculated by:

Inside radius = 1.5 x thickness of plate


Example: for 5mm plate

Bend radius = 1.5 x thickness
                  = 1.5 x 5mm
                  = 7.5mm

Pressing charts

Data sheets from machine manufacturers give pressing information relating to:

The following chart relates to a 80 tonne hydraulic press brake.

Air bending force chart - mild steel


V = vee block opening

IR = inside radius

B = minimum flange length

F = force required to bend

t = material thickness


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