How do you show stamping burr direction on a drawing?

Which face carries the burr on a pierced hole versus a blanked outline?

The burr forms on the face that leaves the cutting edge last: for a pierced hole that is the die side of the sheet, and for a blank pushed out of the sheet it is the punch side of the blank. The rounded rollover sits on the opposite face in both cases.

A sheared edge is not a clean cut through the full thickness. The punch first bends the sheet into the clearance gap (rollover), then shears a smooth band (burnish), and finally the remaining section tears (fracture). The torn material that drags along the cutting edge at the end of that sequence is the burr. Industry guidance from the steel sector describes the same four zones on a punched hole: rollover, burnish, fracture and burr (AHSS Insights, worldsteel).

Which piece keeps which face depends on what the part is. In piercing, the slug is scrap and the strip is the part, so the hole wall carries its burr on the die side. In blanking, the slug is the part (NJIT ME-215 lecture notes define the two operations this way), and the blank's perimeter burr is on the face the punch pushed.

That leads to the result that surprises many designers: if a die pierces the holes and then blanks the outline, with all punches coming down from the same side, the holes and the outline can carry their burrs on opposite faces of the same part. A compound die, which pierces and blanks in one stroke with the blanking punch carrying the piercing die, and a progressive die that frees the part by cutting away scrap around it instead of punching the blank through, are laid out differently. The drawing should state the result it needs, not guess the layout.

How does ISO 13715 indicate burr size and direction?

ISO 13715 uses an edge symbol with a signed size: a plus value permits material outside the ideal edge, such as a burr, and a minus value requires the edge to be broken inside it. A separate clause covers the direction in which that passing or undercut may lie.

The current edition is ISO 13715:2017, published in Europe as EN ISO 13715:2019. It defines an edge of undefined shape as an edge whose shape is not defined on the nominal model, an undercut as a deviation inside the ideal geometrical shape, and a passing as a deviation outside it. Read that way, a burr or a casting flash is simply material lying outside the ideal edge, which makes it a form of passing (ISO 13715:2017, clause 3). That is the conceptual key: in this standard, a burr is not a defect word but an allowance you size.

The indication has three parts: the basic symbol attached to the edge (or placed near the title block to apply to all edges), a sign, and a size in the drawing's units. The sign tells the stamper what is allowed. Plus means a burr up to the stated size is acceptable, minus means the edge must be deburred or broken by up to that amount, and plus-minus allows either within the band.

The standard also provides a way to show toward which adjoining surface the passing or undercut may lie, which is exactly the burr-direction question. The detailed rules and graphics for that are in the paid text, so check the exact form against a licensed copy before you standardize it in a drawing template.

How much burr height should a stamping drawing allow?

Set it from function first, then check it against what clean tooling produces in that material and thickness. Historic mild-steel practice treats a burr under a tenth of the sheet thickness as normal.

For conventional mild and HSLA steels, steel-sector guidance reports that shops have long aimed to keep the burr under one tenth of the sheet thickness, allowing a little more on heavy gauges, and have treated a burr past that point as the cue to regrind or change the cutting edges (AHSS Insights). The same industry guidance gives the recommended die clearance for mild steel as 5% to 10% of thickness per side, rising with tensile strength.

First, a limit expressed as a fraction of thickness scales sensibly across a family of parts, so following that typical practice, a general note such as BURR HEIGHT 10% OF STOCK THICKNESS MAX is a reasonable default for mild steel, with tighter values flagged where function demands them. Second, burr height is a wear signal: the same guidance notes that on mild steel it grows continuously with tool wear and clearance, so the first-article burr is the smallest you will see. Write the limit for the end of a sharpening cycle, not the start.

Clearance cuts both ways. In a university study on 3.00 mm sheet, a blanking clearance of 0.13 mm produced larger burrs than 0.15 mm, with measured mild-steel burrs of 0.192 mm against 0.088 mm, and brass and aluminum producing much smaller burrs than mild steel under the same conditions (Kamarul Adnan et al., 2022). The drawing should set the burr limit and leave clearance to the supplier.

High-strength steels change the picture. For advanced high-strength grades the same steel-sector guidance reports that burr height did not rise with tool hits, and that cut-edge quality, not burr height alone, is the better indicator of when to sharpen. It adds that on these grades burr height matters less to edge stretching than the uniformity of the cut edge; per ISO 16630, the hole-expansion test itself is run at a 12% clearance (AHSS Insights). On those grades, a burr limit alone does not protect a flanged hole.

What should the RFQ say about burrs when sourcing stamped parts overseas?

State the burr side, the height limit, the edges it applies to, and how it will be measured, in words as well as symbols. Drawings sent to a plant in another country, whether in Vietnam, Mexico or elsewhere, are read by people working in a second language, and a plain note survives translation better than a symbol convention the reader may not share.

ISO 13715 symbols and ASME-style notes look nothing alike, and each side tends to read the other's convention through its own. A short checklist prevents most disputes:

• The burr face is marked on a view that shows the thickness, not only on the flat pattern.
• The height limit is a number with units or a stated fraction of thickness, and says whether it applies to all sheared edges or listed features.
• Features with the opposite requirement are flagged individually.
• The measurement method is named: a height gauge or micrometer across the burr, a comparator, or a section on first articles.
• If ISO 13715 symbols are used, the note cites the edition (ISO 13715:2017) so no one reads it against the withdrawn 2000 text.

Ask for a first-article sample with the burr face marked, and keep it as the physical reference for later lots. The RFQ preparation guide covers the rest of the package, and you can send the drawing for a quote with the burr notes as they stand; questions about burr side come back in the quote review, before tooling.