Punch-and-die clearance affects cutting force, burr formation, edge quality and tool life. The recommended percentage changes with both sheet material and thickness, and piercing and blanking can use different values. This reference summarizes Mate Precision Technologies’ 2021 guide and keeps its total-clearance convention explicit so it is not mistaken for a per-side setting.

Sheet Metal Shearing Clearance by Material

Interpret the clearance basis

Mate defines total die clearance as the sum of the gaps on both sides of the punch. Its chart lists total clearance as a percentage of sheet thickness. To find the nominal total gap, multiply the thickness by the selected percentage. If a tooling drawing requires clearance on each side and the punch is centered, divide that total gap by two. Confirm the convention on the drawing or with the die supplier before machining the tool.

For example, the Mate chart gives 25% total clearance for piercing mild steel between 3 and 6 mm thick. At 4 mm sheet thickness, that corresponds to 1.0 mm total clearance, or a nominal 0.5 mm per side for a centered punch. The example is an arithmetic illustration of the published percentage; it is not a new recommendation. Blanking uses a different percentage in the same band, so keep the operation column in view.

The guide also distinguishes aluminum, mild steel and stainless steel by typical shear strength. “Mild steel” is not an exact grade specification, and the stainless category does not identify a particular alloy or temper. Material strength, ductility, hardness, coatings and supplier condition can affect the cut. A manufacturer’s starting chart should be checked against the actual material and tooling style.

Why piercing and blanking differ

In piercing, the hole is the wanted feature and the slug is removed. In blanking, the cut-out piece is the desired part and the surrounding sheet is scrap. Because the functional dimension belongs to a different piece, the punch and die dimensions are arranged differently. Clearance influences which side of the cut shows rollover, burnish, fracture and burr. Selecting a percentage without identifying which part is controlled can make a dimensionally correct tool produce the wrong final feature.

Mate describes proper clearance as a balance: shear cracks from each side join, helping manage punching force, part quality and tool life. Too little clearance can raise force and promote secondary shear cracks. Too much can worsen burr and distortion. Slug shape and the appearance of the cut edge can help diagnose the setup, but they do not replace measurement of the finished feature.

Apply the chart safely

Confirm the press can provide the needed tonnage with reserve, and check that the punch, die, stripper and tool station suit the material thickness. Keep cutting edges sharp and aligned. Use the proper tool clearance around corners and consider part flatness, burr direction and dimensional tolerance. Fine blanking, thick plate, nonmetallic sheet, hardened stock and special shears use other conditions. Do not apply this general punch-press chart to those processes without separate guidance.

Use Mate’s current tooling guidance or contact the tool supplier when the material is outside the listed bands or when edge quality is critical. Trial the setup with representative stock, then inspect hole or blank dimensions and burr height before releasing production.

When setting up a die, record the stock material, actual thickness, punch size and intended operation so the selected row can be checked later. Material names alone can hide different tempers, coatings or strength levels. A test blank lets the operator measure the cut edge and compare the resulting burr with the drawing requirements. Maintain a consistent lubrication and press setup during the trial, and recheck clearance after tool sharpening or replacement. These checks help keep a published starting percentage connected to the tooling condition on the shop floor.

Sources

Values are summarized from Mate Precision Technologies’ Technical Solutions Guide, Revision E (2021), die-clearance chart. Mate defines the shown percentages as total clearance across both sides of the punch.