Burr Height and Burr Direction on Stamped Parts: How to Specify Them on a Drawing
Why buyers ask
A common question from buyers of stamped brackets, clips, covers and enclosures is why parts arrive with sharp edges that scratch fingers, cut gaskets or stop a part from seating. Burr is not a defect of one supplier; it is a normal result of cutting sheet metal between a punch and a die. What decides whether it is a problem is whether the drawing says how large it may be and which side it falls on. This guide explains what controls the burr, how to write it on a drawing and how to check it.
What a burr is and where it comes from
When a punch cuts sheet metal, the edge shows three zones: a rounded entry (rollover), a smooth burnished band and a rough fracture zone that ends in a small raised lip, the burr, on the exit side. The burr forms on the side where the metal leaves the punch, that is, on the die side, so the burr side is set by how the die is built and which way up the strip is fed.
- Die clearance: the gap between punch and die, usually set as a percentage of sheet thickness per side. Too small a gap gives secondary shear marks; too large a gap gives a bigger rollover and a taller burr.
- Tool sharpness: burr height grows steadily as the cutting edges wear, which is why a drawing should state a limit and the first lot should be measured again after a long run.
- Material and thickness: soft, ductile material such as annealed aluminum or copper forms a taller burr than harder grades; thicker sheet gives a larger absolute burr.
- Lubrication and alignment: poor alignment of punch and die gives a burr that is large on one side and small on the other.
How to write burr requirements on a drawing
- Add a general note, for example: all edges deburred, maximum burr height 0.05 mm, burr side as marked. Choose a number you can justify; a tighter number than the function needs only adds cost.
- Mark the burr side on the view with an arrow and the words burr up or burr down. This is the single most useful line because it decides how the die is built.
- Use an edge-condition symbol such as the one defined in ISO 13715 where a specific edge needs its own limit: a positive value allows a burr, a negative value allows an undercut, and zero means a sharp edge.
- Name the critical edges (for example the edge that touches a gasket, a thread or a user's hand) and relax the rest.
- State whether sharp edges must be broken or rounded after cutting, and by how much.
Options for removing or controlling the burr
| Method | What it does | Typical use |
|---|---|---|
| Tighter clearance and scheduled regrinding | Keeps the burr small at the source | Every precision blanking tool |
| Vibratory or tumble deburring | Rounds all edges together with media | Small and medium parts in volume |
| Brushing or belt deburring | Removes the burr on selected edges | Flat parts, larger sheets |
| Coining or shaving a step | Flattens or trims the burr in the die | Parts that must mate or seal |
| Fine blanking | Cuts a smooth edge almost without a burr | Gears, levers and parts with a fully burnished edge |
Deburring is a separate operation with a separate cost, and some surface finishes (anodizing, plating, passivation) also change the edge. Say on the drawing whether the burr limit applies before or after finishing. We can arrange vibratory deburring and other finishing through our production network across Guangdong, Zhejiang, Jiangsu, Shandong and Fujian, and we confirm the route in the quotation.
How to check burr on the first lot
Agree before production which edges are checked, how many pieces from the first lot, the limit and the method. For most parts a sample inspected under magnification or with a profile measurement is enough. Repeat the check after a set number of strokes, because burr height is the first thing to move as the tool wears. For critical parts, ask for a first article inspection report that includes the burr measurement, together with the other dimensions we report to ±0.01 mm on precision features.
What to send for a quote
A 2D drawing with the burr note and burr side marked, a STEP file, material and thickness, finish, the quantity of the first lot and the annual volume, the edges that are critical, and your delivery country. We reply with a quote and a DFM review within 24 hours.
Frequently asked questions
What burr height is normal on stamped parts?
With sharp tooling and correct die clearance, the burr on a blanked or pierced edge is usually a small fraction of the sheet thickness, often in the range of about 5–10 percent. It grows as the tool wears. Because the number depends on material, thickness and tool condition, put a maximum burr height on the drawing instead of relying on a general rule.
How do I tell the supplier which side the burr must be on?
Mark the burr side on the drawing with an arrow or a note such as burr up or burr down, and use an edge-condition notation such as ISO 13715 for the maximum burr height on that edge. The die is built so the burr falls on the side you specify, which is cheap to arrange before tooling and costly to change afterwards.
Can stamped parts be completely burr-free?
Not from a conventional blanking die. Fine blanking gives a very clean cut edge, and vibratory deburring, tumbling, brushing or a coining step can remove or round the burr on conventional parts. Each option adds cost, so ask for them only on the edges that touch people, seals or mating parts.
How is burr height measured?
Typically with an optical or profile measurement of a sample of parts from the first lot, using a feeler or a profilometer for a closer look. Agree the edges to be measured, the number of pieces and the limit before production starts, and repeat the check at agreed intervals as the tool wears.
Does burr direction change the price?
Not if it is decided at the drawing stage. Changing it after the die is built can mean a new punch and die set or an extra operation, so mention it in the first request for quotation.
Send your drawing for a quote
Send the drawing with the burr note and burr side, material, thickness, finish, first-lot and annual quantities and your delivery country. We reply with a quote and a DFM review within 24 hours.