Why Is Claw Height Held to 0.05 mm on a Bezel Ring?

Claw height carries a two-sided limit, 1.2 ± 0.05 mm, because both directions fail. A tip standing high lifts the crystal off its seat, and a tip sitting low leaves the crystal unheld. Trimming the inner claws is what puts that height on a Zamak 5 ring cast to ASTM B86 AC41A, so the window is set by an operation, not by the raw casting.

The part is a Ø26 × 2.0 mm ring, 1.8 ± 0.2 g, with a 0.8 mm wall and three claws set 120° apart, all design targets. Each claw is read from the ring base face, the same datum the ring presses against inside the case.

What happens when a claw sits 0.05 mm too high?

A high tip becomes the only claw in contact, so a load meant for three points arrives at one. The ring rocks on that claw and the crystal lifts on the opposite side, which shows up as a bezel that will not seat flat however hard the press pushes.

Cutting the tip removes metal, so a worn trim stop that lets the cut run shallow leaves one claw proud of its neighbours. The fault is quiet at the bench and loud at assembly, and the ring cannot be pressed a second time to close the gap. Whoever signs the first-article report owns that number.

What happens when a claw reads 0.05 mm low?

A low tip never reaches the crystal edge, so the ring holds on two claws and the third does nothing. The crystal can turn or lift under the bezel while the ring looks seated, and a press-force reading inside the 80–200 N band proves only that something stopped the stroke, not that all three tips touched.

The low side fails more quietly than the high side. Nothing looks wrong at assembly, the fault surfaces when the case is handled, and there is no rework path because the assembly does not come apart twice. A ring that measures low is scrap; nothing on the bench brings the tip back.

Which process moves claw height after casting?

Trimming the three claws does, after the casting is degated and tumbled on the tumbling line and before it reaches plating. A die casting tool leaves a tip that still has to be cut to length, so a better die on its own does not deliver 1.2 ± 0.05 mm.

Two sources push the tip out of the window. A worn die casts the claw shorter across the 500,000-shot design target, and a trim pass that cuts too deep takes the rest. Neither is visible on a finished ring without a reading, so the step is quoted as its own line and checked as its own step.

How is claw height measured on the floor?

Claw height is read with a height micrometer, from the base face to the tip, with the ring lying flat on a surface plate. The datum is the face that seats in the case, so the number means what the assembly needs rather than what the outside of the band happens to measure.

Calipers invite a wrong reading. Their jaws span the band as well as the claw, so the wall thickness of 0.8 mm enters the result, and within a 0.05 mm window that error passes rings that should be rejected. The gauge and the reading it produced belong in the first-article report together.

When does the tool need rework for claw height?

When the cast tip falls below the low limit, trimming has nothing left to remove. Cutting cannot add metal, so a short casting is a tool problem, and reworking the die is the only route back into the window.

One tool holds eight cavities at a 500,000-shot design target, so a height drift is a tool event rather than a single bad part. A repair stops the press, which means the schedule needs a window reserved before the run starts, not after the first rejects come back.

Claw height is the one callout read on the ring alone, without a case, a crystal or a press. Put the window, the datum and the gauge on the drawing and the first article answers the trimming question before the batch runs.