The Samples Felt Smooth, but a Review Said the Production Dish Rack Cut a Finger
Sharp Edge and Burr Inspection Guide - Why Burrs and Sharp Edges Form, Acceptance Criteria Such as Burr Height, Edge Treatment and the Sharp Edge Test, Deburring Methods Including Vibratory, Brush and Electropolishing, Die Sharpening Control, Spec and Limit Sample Items, Stage-by-Stage Checks and a Checklist

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A Korean brand selling kitchen storage products had 5,000 two-tier dish drying racks made at a stainless steel fabrication factory in Yangjiang, Guangdong. Running a hand over the two samples found nothing that caught, and the pre-shipment inspection passed on appearance, dimensions and load testing. But three weeks after launch, a review appeared: "I cut my finger taking a bowl out after washing up." Similar complaints followed, and in the end the brand stopped sales and had to re-inspect 1,800 units of stock.

The cause turned out to be burrs (毛刺) left on the stamped edges of the drip tray and side panels. The samples had been stamped right after the die was sharpened, and a worker had filed each one by hand. Midway through production, the die edges wore down and the burrs grew. To make the delivery date, one lot also had its vibratory finishing time cut in half. The pre-shipment inspection had no item that checked for burrs.

Sharp edges and burrs hardly show up in photos. They are discovered only after a customer touches them, and at that point they are no longer a quality problem but a safety problem. This guide covers why burrs and sharp edges form, how to set the line between acceptable and defective, deburring (去毛刺) methods, and what to check in your spec sheet and inspections.

"Smooth with no burrs" is not a specification. Production units are as safe as the samples only when every area has an allowable burr height and edge treatment defined in numbers, and you confirm with records that die maintenance and deburring actually meet that standard.

1. Why Burrs and Sharp Edges Form

A burr is a thin raised ridge left on an edge when metal or plastic is cut, stamped or machined. Samples get time-consuming hand finishing, while production units are made by the thousands within a fixed cycle time, and most problems come from that gap. These are the causes we see most often.

• Die wear: As the stroke count on a stamping die (冲压模) builds up, the cutting edges dull and the gap between punch and die opens, so burrs grow. This is where the quality gap between the first and last lots comes from.
• Wrong clearance: If the punch-to-die gap is too large or too small for the sheet thickness, burrs are large from the start.
• Laser and plasma cutting: Molten metal solidifies on the underside of the cut as dross (挂渣).
• Injection flash: Resin leaks out along the mold parting line or around ejector pins, leaving thin fins (披锋·毛边). Mold management is covered in Episode 33.
• Cut tube and wire ends: Without finishing after cutting, the inside and outside edges are left sharp.
• Shortened or skipped deburring: This is the first process to be cut when delivery is tight, and the difference is hard to see from the outside.

Plating and painting matter too. Plating over a burr hardens it, and paint hides burrs so they are easy to miss at inspection, but once the coating wears off the edge is exposed again. For paint quality, see Episode 130.

2. Where Is the Line? Setting the Criteria

Removing every burr completely costs too much. It is more realistic to set an allowable range for each area, and the items below are useful references when you do.

Separate Touch Areas from Hidden Areas

Even within one product, areas users touch directly and areas hidden after assembly need different criteria. Mark the touch surfaces on the drawing or spec sheet and state that no burrs or flash are allowed there, and the factory will know exactly where to focus its deburring. Managing this together with dimensional criteria is covered in Episode 134.

Children's Products Have Their Own Test Standards

For children's products and toys, a sharp edge test is part of the safety standard. In Korea, the common safety standard for children's products and the toy safety standard also cover sharp edges and points, so failing this item in KC certification testing directly affects customs clearance and sales. For children's product import requirements, see Episode 65.

3. Deburring Methods and What to Check

Once the criteria are set, you need to choose the process that will meet them. Here are the deburring methods commonly used in Chinese factories.

Deburring has to be managed together with the die. Sharpening the die at a fixed stroke count costs less and gives steadier quality than grinding off ever-larger burrs downstream. Have the factory record the sharpening interval (e.g. every 30,000 strokes) and the last sharpening date, and write mold ownership and maintenance responsibility into the contract, as covered in Episode 109.

4. Items for Your Spec Sheet and Limit Samples

A sentence like "finish smooth with no burrs" is interpreted differently by every factory. Put the items below in a table for each area and attach it to your spec sheet or BOM. For writing a BOM, see Episode 59.

Touch criteria are hard to put into words, so limit samples (限度样品) matter a great deal here. Pick parts right on the boundary between pass and fail, have both sides sign them, and make sure the factory and the inspector judge against the same samples.

5. How to Check at Each Stage

Sample Stage

When samples arrive, run a cotton glove or stocking over every edge users can touch, and check anything that catches with a magnifier or burr height gauge. For children's products, send the samples to an accredited lab for a sharp edge test. Also ask the factory whether the samples came off a freshly sharpened die and whether they were hand-finished, so you can anticipate how production units will differ.

First Article and Production Stage

On the first day of production, check the deburring conditions (finishing time, media type) and the die sharpening records. At the pre-production meeting, also confirm that the A/B surface split and the limit samples have been built into the work instructions. For first article procedures, see Episode 123.

Pre-Shipment Inspection Stage

A standard AQL inspection focuses on appearance and dimensions, so burrs are often passed over unless they are obvious. Add an A surface touch check, burr height measurement (5 pieces per lot) and a comparison of early and late production lots to your inspection checklist. The late production lots must be included, because that is where burrs grown from die wear are caught. For pre-shipment inspection, see Episode 100.

6. Sample Wording to Send the Factory

Putting the wording below in your purchase order or spec sheet takes deburring standards out of the factory's discretion and makes it easier to assign responsibility if a cut-injury claim arises.

"所有用户可触及部位（A面）须按我方确认的《毛刺及锐边标准》执行，毛刺高度不得超过0.05mm，边角须倒圆角R0.3以上。去毛刺工序（振动研磨时间、磨料种类）未经我方书面确认不得缩短或取消。冲压模具须每3万冲次修模一次并保存记录。出货检验须对A面进行全检手感检查，并每批抽测毛刺高度至少5个，提供检验记录及前后期批次对比。"
(All areas users can touch (A surface) must follow our approved "Burr and Sharp Edge Standard": burr height must not exceed 0.05mm, and edges must have a radius of R0.3 or larger. The deburring process (vibratory finishing time, media type) must not be shortened or removed without our written approval. Stamping dies must be sharpened every 30,000 strokes with records kept. At outgoing inspection, carry out a 100% touch check on A surfaces, measure burr height on at least 5 pieces per lot, and submit the inspection records along with a comparison of early and late production lots.)

7. Three Real Cases

These are anonymized versions of patterns we often see in consultations. Amounts and figures are examples.

Case 1 — Stainless Steel Dish Rack

This is the case from the start of the article. Working with the factory, the brand had the die re-sharpened and added an R0.3 radius to the drip tray's outer edge. The vibratory finishing time was fixed at 40 minutes or more and recorded for every lot, and a cotton glove touch check and burr height measurement on late production lots were added to the pre-shipment inspection. Re-inspecting and hand-finishing the 1,800 units in stock cost about 20,000 yuan, but the lost sales during the stop and the lower star rating were a far bigger loss.

Case 2 — Toddler Building Blocks

A company importing injection-molded building blocks failed the sharp edge item during KC certification testing. It turned out that flash had formed along the mold parting line, and while the factory had been trimming it with a knife, some cavities had been missed. Instead of relying on trimming, the parting surface of the mold was repaired, and after that almost no flash appeared at all.

Case 3 — Painted Steel Toolbox

A company selling powder-coated steel toolboxes received returns saying "the inside of the handle scratches your hand." The burrs inside the handle holes had not been removed before painting, and the coating covered them so they could not be seen at inspection. After a few uses, the coating wore through and the edge was exposed. Handle hole deburring and inspection were then added before painting, and the inside of the handle was checked separately at pre-shipment inspection. Liability for product defects is covered in Episode 53.

8. Common Mistakes

• Writing only "smooth with no burrs" in the spec sheet without defining an allowable burr height in numbers
• Not separating areas users touch from areas that are hidden
• Judging production quality from samples made right after the die was sharpened
• Not fixing deburring time and conditions in the contract
• Not checking for burrs hidden under paint or plating
• Leaving late production lots out of the pre-shipment inspection

9. Burr and Sharp Edge Quality Checklist

Spec and Contract Stage

• Touch areas (A surface) and hidden areas (B surface) are marked on the drawing
• Allowable burr height and edge treatment (R/C) are set in numbers for each area
• Deburring conditions and die sharpening intervals are written into the spec sheet
• A prior-approval clause covers any shortening or skipping of processes

Sample and First Article Stage

• Every A surface edge on the samples has been touch-checked
• Sharp edge test results have been obtained for children's products
• Borderline pass/fail limit samples are signed and kept by both sides

Production and Shipment Stage

• Per-lot deburring records and die sharpening records are kept
• The pre-shipment inspection includes an A surface touch check and burr height measurement
• Early and late production lots have been compared

Wrapping Up - Turning "Smooth" into Numbers

Burrs and sharp edges rarely show up in photos or in a standard inspection, and they come to light only after a customer gets hurt. Because this is a safety problem rather than a cosmetic defect, a single review can stop sales. Setting numeric criteria for each area and having the factory keep die and deburring records does not cost much.

There is something you can do right now. Take one of the products you currently sell, put on a cotton glove and run it over every edge a user can touch. If anything catches, put together a burr standard table and limit samples and send them to the factory before your next order.

StartMade supports you on the ground, from writing burr and edge standard tables and finalizing limit samples to checking die sharpening and deburring records and carrying out touch checks and burr height measurement before shipment. If you already have cut-injury claims, we start by re-inspecting your stock; if you are preparing a new product, we start with the standard table.