Sheet Metal Edge Rounding

How Much Edge Rounding Does Sheet Metal Need?

There is no single value. The radius comes from the drawing or the coating specification, and the right answer depends on why the edge is rounded in the first place.

For coated steel, ISO 8501-3:2006 defines three preparation grades. At P1 and P2, no part of a punched, sheared, sawn or drilled edge may be sharp. At P3, those edges must be rounded to a radius of not less than 2 mm, and thermally cut edges must also have the cut face removed. Check which grade your coating specification names before you set a target.

More radius also means more removal: as the geometry section below shows, doubling the radius removes about four times the cross-section at the corner. Specify the radius the part needs, not the largest one a machine can produce.

An edge break is not a specified radius

A lightly eased edge and a defined radius are different results. An edge-break instruction may allow a small chamfer or irregular softening, while a radius requirement describes a curved profile. The drawing should make clear which result is needed and where it applies.

Specify the upper and lower edges separately when their requirements differ. Include holes and slots in the edge map rather than assuming that a statement about the outside contour covers them.

Why the same part can have different edges

A flexible abrasive tool removes material where it sweeps across the corner. Contact changes with the direction of approach, the space around the edge and the support beneath the part. An exposed outside corner and a recessed internal contour do not offer the tool the same access.

For a part with long edges and small openings, inspect both. A good result on the leading edge should not be used as a substitute for examining the trailing edge or the inside of a slot. Keep part orientation on the trial record so the result can be reproduced.

More radius means more material removal

For an ideal square corner rounded to a quarter-circle of radius r, the cross-sectional area removed is (1 − π/4) × r². Doubling r therefore multiplies that ideal removed area by four.

This is a geometric illustration, not a machine output prediction. It explains why a larger radius deserves a separate process trial; it does not mean processing time or abrasive cost will rise by exactly four times. Actual contact, burr condition and tooling also matter.

Use the radius required by the drawing or coating specification. There is no universal radius that should be assigned to every TFON application.

Measure the profile, then assess the next operation

Check the profile with a method suited to its size and tolerance. A radius gauge can provide a comparison where appropriate; tighter or complex profiles may need optical measurement. Inspect a defined set of outer and internal edges rather than choosing the easiest corner.

For coated parts, edge geometry is only one part of the process. Surface preparation, coating application and curing still determine whether the finished coating meets its specification. A photograph of a rounded edge does not establish coating performance.

Edge Rounding Tools and Machines

Edge rounding tools range from hand tools to conveyor machines. The choice follows part volume, part size and which edges need the radius.

• Hand tools: files, deburring blades and radius scrapers. They are cheap and flexible but slow, and the radius depends on the operator.
• Hand-held edge rounding machines: portable tools with radius cutters or flap discs that run along plate edges. They give a more even radius on straight edges but do not reach small holes well.
• Manual machines: the operator guides a rotating disc head over a part held on the table. The TFON Lite Surfacer uses an edge rounding disc for this and suits prototypes and mixed batches.
• Conveyor edge rounding machines: parts pass under rotating flap brushes that work the outer contour and the edges of holes and cut-outs. The TF-R-3013: 1300 mm edge rounding machine rounds edges and removes oxide on burr-free parts; the TF-RB-3013: 1300 mm deburring machine adds a belt station, so the burr comes off first in the same pass.

All TFON edge rounding configurations are compared on the deburring and edge rounding machines page.

Single-Sided vs Double-Sided Edge Rounding

A sheet metal part has edges on two faces. Single-sided edge rounding treats the edges on the face that meets the tool. Double-sided edge rounding treats both, either with tools above and below the part or with two passes.

TFON Surfacer® machines are single-sided: they process one face per pass. To round the edges on the other face, the part is turned over and run through a second time. No TFON model rounds both faces in one pass.

In practice this means:

• Check what the drawing asks for. A part that is powder coated all over usually needs both faces; a part that only needs safe handling may need one.
• If both faces need a radius, plan a place to turn the part and include the second pass in the output and cost estimate.
• A saved recipe lets the second pass start from the approved setting, so both faces are processed the same way.
• Inspect the edges on both faces. A good radius on the first face says nothing about the second.