Sheet Metal Guide 17

When To Use A Physical Bend Test Coupon

Original practical guidance for flat pattern planning, bend allowance decisions, and shop-ready sheet metal communication.

When To Use A Physical Bend Test Coupon matters because a flat pattern is only useful when the shop can bend it consistently. The calculator gives a fast reference, but the final drawing should also reflect material condition, press brake tooling, grain direction, and inspection expectations.

For stainless steel, start with the nominal thickness, inside radius, bend angle, and a realistic K factor. The displayed flat length should be checked against your forming method, especially when the part uses bottoming or tight cosmetic requirements.

Practical use

Enter known dimensions first and avoid changing more than one assumption at a time. If the flat length changes dramatically when K factor moves from 0.40 to 0.44, make a bend coupon or ask the shop for proven values from similar material and tooling.

The cone and cylinder tools support layout work for reducers, ducts, sleeves, and rolled shells. Use the results as a clean communication aid, then verify seam allowance, trimming, weld preparation, and forming springback.

Before production

Review the drawing revision, material specification, bend direction, tolerance callouts, and inspection temperature. For critical parts, compare the calculated blank with first-article measurements before releasing batch production.