Quality Control

Edge Finish Specs for Custom Pins, Coins and Keychains

Why Approved Artwork Still Fails at the Edge

Most artwork approvals show the front face, enamel colors, logo detail and plating finish. They rarely define the outside edge, pierced cutouts, split-ring hole, coin rim or back perimeter. Those unmarked areas often create the first complaint: a pin scratches its backing card, a keychain cuts through an OPP bag, or a challenge coin feels unfinished because a rim burr sits under the plating.

Edge finish is a functional quality requirement, not only a cosmetic preference. A sharp 90 degree metal edge concentrates plating stress, traps polishing compound, wears through topcoat faster and can damage fabric, paperboard or plastic packaging during transit. For corporate gifts, uniform accessories, museum retail, sports merchandise and event giveaways, the buyer should define edge condition before tooling starts.

The practical specification is not complicated. The drawing should state the required radius or chamfer where geometry allows, the maximum burr height, the deburring method, the plating expectation at corners and the inspection method. If these points are left until final inspection, the factory may have only two poor options: over-polish the part and soften the logo, or ship a product that passes visually but feels sharp in use.

Where Edge Defects Start in Production

Stamped iron and brass pins usually create the sharpest edges at the blanking perimeter and pierced holes. The die shears the sheet and leaves a rollover zone on one side and a fractured zone on the other. With correct die clearance, burrs on 1.2 to 1.8 mm iron are usually controllable below 0.03 to 0.05 mm after tumbling. With worn tooling or excessive clearance, the fractured edge becomes jagged and remains visible after nickel or gold plating.

Zinc alloy die-cast keychains and 3D badges have different risks. The parting line, gate trim, ejector-pin marks and drilled or cast ring holes can leave raised seams or small tear marks. Antique brass can hide some visual texture, but bright nickel, black nickel and mirror gold reveal waves, drag marks and gate repairs. For keychains, the ring hole is a high-wear zone because the split ring rotates against the plating during use.

Etched stainless steel, brass charms and thin nameplates can feel knife-like because the starting sheet is often only 0.3 to 0.8 mm thick. Chemical etching gives accurate profiles, but it does not naturally create a soft edge. If the item will be worn, handled or packed loose in bags, specify perimeter deburring rather than accepting an as-etched edge.

Process	Typical thickness	Common edge risk	Practical edge spec
Stamped iron soft enamel pin	1.2 to 1.8 mm	Reverse-side blanking burr	Burr below 0.05 mm; soft tumble before plating
Stamped brass badge	1.0 to 2.0 mm	Sharp pierced holes and cutouts	Inside edge radius 0.10 to 0.20 mm where tool allows
Zinc alloy keychain	2.5 to 4.5 mm	Parting line, gate scar, rough ring hole	Parting line polished flush within +0.05 mm; ring hole deburred
Die-struck brass challenge coin	3.0 to 5.0 mm	Rim burr, reed tip sharpness	Rim chamfer 0.20 to 0.30 mm or burr below 0.03 mm
Etched stainless charm	0.3 to 0.8 mm	Thin, cutting outside profile	Full perimeter deburr; no cotton-glove snag

Define Radius, Chamfer and Burr Limits Before Tooling

The safest way to prevent sharpness is to define an edge radius or chamfer on the production drawing. For most enamel pins and small badges, a 0.10 to 0.20 mm soft radius is enough to remove cutting feel without visibly changing the outline. For thicker zinc alloy keychains and 3.0 to 5.0 mm coins, 0.20 to 0.40 mm is more realistic because the user handles the side wall as much as the front face.

Do not over-specify the edge on fine artwork. A 0.30 mm radius on a 0.50 mm raised line can erase detail during polishing. For narrow letters, star points, skyline outlines and openwork bridges, use a performance requirement instead: no loose burr, no cutting feel, no fiber snag, and no raised burr above 0.05 mm unless approved on the pre-production sample.

A chamfer is often better than a full roundover when the product needs a crisp premium look. A challenge coin with a 0.25 mm by 45 degree chamfer on both faces can look cleaner than a heavily rounded coin. On enamel pins, however, too much chamfer can reduce metal wall height and make enamel fills appear shallow near the perimeter.

Product area	Recommended edge condition	When to avoid it	Inspection note
Outside pin outline	0.10 to 0.20 mm soft radius	Very thin etched items below 0.8 mm	Touch check and 10x loupe
Keychain outer edge	0.20 to 0.40 mm radius or chamfer	Brand shapes requiring sharp angular geometry	No OPP bag cutting after packing trial
Coin rim face edge	0.20 to 0.30 mm chamfer	Text or reeding too close to rim	Check with caliper or radius gauge
Internal cutouts	Deburred; no loose burr above 0.05 mm	Slots below 1.0 mm width	Cotton swab snag test
Split-ring hole	Rounded entry edge; no plating flake	Thin sheet below 1.0 mm	Fit ring and rotate 20 cycles

Choose the Deburring Method by Geometry and Finish

Vibratory tumbling is the standard low-cost method for small metal giveaways. Parts run with ceramic or plastic media, water and compound until high burrs are knocked down. Typical cycle time is 20 to 60 minutes for simple stamped pins and flat keychains. It is efficient, but it can dull raised text, thin lines and sharp logo corners if the design has fragile detail.

Hand polishing gives more control on premium pieces, thick die-cast keychains, 3D coins and parts with visible gates. Workers can target the perimeter, parting line and ring hole without flattening the artwork face. The trade-off is labor cost and consistency. At 1,000 pieces, hand edge polishing may add about USD 0.03 to 0.08 per simple pin and USD 0.08 to 0.20 per complex cast keychain, FOB China, depending on perimeter length and number of holes.

Barrel polishing is economical for simple stamped blanks but risky for enamel pins with posts, thin protruding points or openwork. Magnetic polishing can reach small internal holes and thin stainless parts, but it is less effective on heavy die-cast pieces. The plating finish also changes the decision: bright nickel, black nickel and mirror gold need cleaner metal preparation than antique brass or matte black because reflective finishes magnify waves and scratches.

• Use vibratory tumbling for simple stamped pins, coins and flat keychains with starting burrs below 0.10 mm.
• Use hand polishing for thick cast parts, visible gates, premium coins and sharp brand silhouettes.
• Avoid heavy tumbling on star points, small letters, openwork bridges below 1.2 mm and raised lines below 0.3 mm.
• Request one raw metal sample when the design has many cutouts; it shows edge risk before plating hides defects.
• Confirm that main deburring happens before plating; post-plating cleanup should be limited and controlled.
• Ask the factory to flag artwork areas where edge softening may change logo accuracy before mold cutting.

Plating Thickness and Edge Coverage

Plating does not fix a burr. It makes the burr brighter, harder and more likely to flake when the item rubs against a split ring, backing card or fabric. If raised metal remains on iron, brass or zinc alloy, copper and nickel build over the defect. The top finish then cracks at the high point during handling or packing.

A common decorative stack for pins and keychains is copper strike, 5 to 10 microns of nickel, then a thin top finish such as gold, black nickel, imitation rhodium or color electrophoresis. Premium coins or outdoor-use keychains may require thicker nickel or a clear protective coating, but buyers should not rely on plating thickness alone. Edge preparation before plating is still the main control.

Edges and corners are difficult areas for uniform plating coverage. A sharp corner can receive high current density on the point while adjacent valleys remain thinner. For products used on keys, bags or uniforms, specify both smoothness and coverage: no exposed base metal at the perimeter, no black spots after neutral salt spray if corrosion testing is required, and no flaking after the ring rotation or tape test agreed in the inspection plan.

Finish	Edge sensitivity	Suggested buyer note	Typical cost impact
Bright gold or nickel	High	No visible burrs, pits or polishing waves on perimeter	Low to medium; mainly polishing time
Black nickel	Very high	No raised burrs; defects show as bright scratches	Medium when hand polishing is needed
Antique brass or antique nickel	Medium	Edges smooth by touch; antique wipe consistent	Low
Matte black paint or e-coating	Medium	Deburr before coating; no chipped corners	Low to medium
Epoxy dome on pin face	Low on face, high at perimeter	Epoxy must not overflow onto sharp outside edge	Low if artwork allows clearance

RFQ Wording That Factories Can Quote

A useful RFQ does not say only smooth edge. Smooth is subjective, and the factory cannot estimate labor accurately. Define the critical zones: outside perimeter, internal cutouts, split-ring hole, brooch pin area, coin rim and any point that contacts packaging, apparel or the user’s hand.

For standard promotional pins, a practical mass-production requirement is: no burr visible at 10x magnification, no burr felt by fingertip, and no raised metal burr above 0.05 mm on the back edge. For premium retail, uniform or collector products, tighten the visual requirement and add a cotton-glove or cotton-swab snag test. For low-cost event giveaways, minor polishing marks on the reverse may be acceptable if the front edge is safe and the backing card is not damaged.

Also specify tolerances that support the edge requirement. A 30 mm pin with an outside size tolerance of +/-0.20 mm cannot keep a perfectly sharp geometric outline after tumbling. A reeded coin should state whether reed tips must remain crisp or softened; aggressive polishing can reduce reed depth by 0.05 to 0.15 mm.

• State construction clearly: for example, 1.5 mm iron soft enamel pin, 3.0 mm zinc alloy keychain or 4.0 mm brass coin.
• Mark critical edge zones on the drawing: perimeter, cutouts, ring hole, rim, pin back and attachment points.
• Set a measurable burr limit: no loose burrs, no sharp feel and raised burr below 0.05 mm unless approved.
• Define inspection method: fingertip check, cotton swab snag test, 10x loupe or caliper check for chamfer size.
• Provide packaging details because an edge that is safe in a tray may still puncture an OPP bag in transit.
• Ask whether polishing may soften fine artwork so the trade-off is approved before tooling starts.

Inspection Plan: Sample, Inline and Final AQL

Edge quality should be checked at three stages. First, inspect a raw metal or unfilled sample before plating when the design has openwork, deep relief, reeded edges or a functional ring hole. Second, approve a pre-production sample after final plating, enamel, epoxy and assembly. Third, include edge criteria in final inspection so the shipment does not pass only because the front artwork looks correct.

For final inspection, a common approach is General Inspection Level II with AQL 1.5 for major defects and AQL 4.0 for minor defects on standard promotional orders. A cutting edge, loose metal burr, plating flake at the edge, broken attachment, cracked ring hole or exposed base metal on a visible perimeter should be major. Slight polishing haze on a non-visible reverse side may be minor if it does not affect safety, plating adhesion or packaging.

Functional tests should be simple enough for a production inspector to repeat. Run a cotton swab around the outside edge and internal cutouts; fibers should not catch. Rotate the split ring through the keychain hole 20 cycles; plating should not flake and no burr should scrape the ring. For pins, press the product against its backing card and slide it 30 mm under normal hand pressure; it should not cut the card or scrape printed ink.

Check point	Tool or method	Accept	Reject
Outside perimeter	Fingertip and 10x loupe	Smooth touch; no raised burr	Sharp feel, lifted metal or cutting point
Internal cutout	Cotton swab snag test	No fiber snag or loose burr	Fiber catches or metal sliver visible
Split-ring hole	Ring rotation 20 cycles	No flake and no scraping burr	Plating chip, rough scraping or exposed base metal
Coin rim	Visual, touch and caliper check	Uniform chamfer or reed depth	Uneven seam, sharp reed or rim burr
Packed sample	Shake test in final bag or card	No bag puncture, card scratch or debris	Punctured OPP, scratched card or loose metal

MOQ, FOB Price and Lead-Time Impact

Edge finishing rarely changes MOQ by itself, but it can change the best production route. For enamel pins, brooches and small badges, sampling or small runs often start at 100 pieces, while 300 to 500 pieces is usually more efficient for mass production. Zinc alloy keychains and custom coins can also start around 100 pieces, but 300 pieces and above normally gives steadier unit pricing because tooling, polishing setup and plating rack loading are spread across more units.

FOB pricing depends on size, metal, finish, color count, attachment and packaging, but edge requirements can be estimated. As a practical China factory range, a 30 mm soft enamel iron pin at 500 pieces may be USD 0.45 to 0.95 FOB. Adding hand cleanup to a complex outline may add USD 0.03 to 0.08 per piece. A 50 mm zinc alloy keychain at 500 pieces may be USD 1.10 to 2.40 FOB, with premium gate, perimeter and ring-hole polishing adding USD 0.08 to 0.20 per piece.

Lead-time impact is usually modest when the requirement is known before production. Extra tumbling or standard polishing may add 0 to 2 days. Hand finishing on complex cast parts can add 2 to 4 days. If tooling must be remade because cutouts are too narrow, text is too close to the rim or the drawing did not allow enough radius, the delay can be 5 to 10 days. Edge specifications belong in the RFQ and proof stage, not in the final complaint.

Order type	Typical MOQ	Normal lead time	Edge-spec impact
Simple enamel pin	100 to 300 pcs	12 to 18 days after artwork approval	Add 0 to 2 days if standard tumble is enough
Complex openwork badge	300 to 500 pcs	15 to 22 days	Add 1 to 3 days for sample review and hand cleanup
Zinc alloy keychain	300 to 500 pcs	18 to 25 days	Add 2 to 4 days for gate and ring-hole polishing
Challenge coin	100 to 300 pcs	18 to 28 days	Add 1 to 3 days for rim inspection and polishing
Etched thin charm	500 pcs	12 to 20 days	Add 1 to 2 days for full perimeter deburr

For standard promotional orders, a compact requirement is enough: no sharp edges, no loose burrs, burr height below 0.05 mm, no cotton-swab snag and no OPP bag puncture after packing trial. For premium retail, uniform or collector products, add a defined radius or chamfer, 10x loupe inspection, split-ring rotation test and AQL defect classification. If the design has openwork below 1.2 mm, fine points or bright plating, ask the factory to comment on edge risk before mold cutting.

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