# FlatBend: Sheet Metal Unfold — Bend allowance & flat pattern

> Bend allowance & flat pattern (iPhone/iPad app by Yoshifumi Sato.)

- Source: https://appshunter.io/ios/app/flatbend-sheet-metal-unfold/id6794622503 (this page in markdown: same URL + `.md`)
- Developer: [Yoshifumi Sato](https://appshunter.io/developer/6780413827)
- Category: Utilities
- Price: $3.99
- Age rating: 4+
- Requires: iOS 17.0 · 13 MB
- Languages: American English, Japanese
- Released: 2026-07-28
- Data updated: 2026-08-01
- User reviews in markdown: https://appshunter.io/ios/app/flatbend-sheet-metal-unfold/id6794622503/reviews.md

## What is FlatBend?

FlatBend is a fast, precise flat-pattern (blank length) calculator for sheet metal workers. It runs fully offline, is a one-time purchase, and has no ads or tracking.

WHAT IT DOES
- Single-bend quick calc: from thickness, inside bend radius, bend angle and K-factor, see bend allowance (BA), bend deduction (BD), outside setback (OSSB) and neutral radius instantly.
- Multi-bend flat pattern: lay out flanges (outside mold-line lengths) and each bend to get the total flat length automatically (Σ outside − Σ BD).
- Reverse solve: fix the flat length and solve one unknown flange.
- K-factor: presets 0.33 / 0.40 / 0.446 / 0.50, or an auto estimate from R/T (air-bend guide). Manual measured values are welcome too.
- Units: mm and inch, with fraction display (1/16, 1/32, 1/64).
- Angle: switch between bend angle and included angle.
- History: name, save and reload jobs, each with a bend-profile diagram.

METHOD
Neutral radius = R + K*T
Bend allowance BA = (pi/180)*A*(R + K*T)
Outside setback OSSB = (R + T)*tan(A/2)
Bend deduction BD = 2*OSSB - BA
Flat length = sum of outside flange lengths - sum of BD per bend

NOTE
Results are geometric estimates (K-factor method). K-factor varies with material, process and tooling. For precision, enter the measured K-factor from a test bend.


## Version history (last 1 release)

### 1.0 — 2026-07-28

No release notes.

## More apps by Yoshifumi Sato

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- [かんじ3年生 小学3年の漢字ドリル](https://appshunter.io/ios/app/3-3/id6790055787)

All apps by Yoshifumi Sato: https://appshunter.io/developer/6780413827

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-08-01.*