Enter Blank and Bend Data
Example Data Table
| Case | Mode | Bends | Angle | Thickness | Radius | K-factor | Legs | Typical use |
|---|---|---|---|---|---|---|---|---|
| Small bracket | Tangent length | 1 | 90° | 1.2 mm | 1.5 mm | 0.33 | 35, 55 | Simple angle part |
| U channel | Tangent length | 2 | 90° | 1.5 mm | 2.0 mm | 0.33 | 40, 80, 40 | Folded channel layout |
| Panel flange | Outside mold line | 2 | 90° | 2.0 mm | 3.0 mm | 0.38 | 50, 120, 50 | Finished outside dimensions |
Formula Used
The calculator estimates flat blank size by combining straight lengths, bend growth, trim, kerf, hems, overlaps, and safety margins.
Bend allowance:
BA = A × (R + K × T)
Here, A is bend angle in radians. R is inside radius. K is K-factor. T is material thickness.
Outside setback:
OSSB = tan(A / 2) × (R + T)
Bend deduction:
BD = 2 × OSSB - BA
Flat length by tangent mode:
Flat length = Sum of straight tangent legs + Total BA
Flat length by outside mode:
Flat length = Sum of outside mold line legs - Total BD
Final minimum length:
Minimum length = Raw flat length + trims + overlap + hem + kerf + safety margin
Final minimum width:
Minimum width = Finished width + side trims + kerf + width safety margin
How to Use This Calculator
- Select millimeters or inches.
- Choose the dimension mode that matches your drawing.
- Enter the number of bends and active leg lengths.
- Add angle, thickness, inside radius, and K-factor.
- Enter trims, kerf, hem, overlap, and safety margins.
- Add sheet size and nesting gap for sheet yield estimates.
- Press the calculate button.
- Download the result as CSV or PDF for job records.
Minimum Blank Size Guide
Why Blank Size Matters
A sheet metal blank is the flat piece cut before bending. Its size controls the final part size. A small error can create short flanges. A large error can waste material. This calculator helps estimate a practical starting blank. It includes bend allowance, bend deduction, trims, kerf, hems, and margins. It also checks sheet nesting. That makes it useful for early layout planning.
Bend Allowance and Material Stretch
Metal stretches during bending. The outside surface grows longer. The inside surface compresses. Between them sits the neutral axis. The K-factor describes its position through the thickness. A low K-factor places it nearer the inside surface. A high K-factor moves it outward. The bend allowance formula uses this position. It estimates the arc length needed around each bend.
Choosing the Right Mode
Use tangent length mode when your straight leg dimensions stop at bend tangency points. This is common for flat pattern work. Use outside mold line mode when your drawing uses outside virtual sharp dimensions. That mode subtracts bend deduction. Use custom modes when your shop already has tested bend data. Tested shop data is often more accurate than general formulas.
Allowances Beyond Bends
A real blank needs more than bend math. Cutting kerf removes material. Trims provide cleanup stock. Hems need fold material. Seams may need overlap. Safety margin covers process variation. These values should match your tooling and material. Thicker stock may need larger radii. Softer material may stretch more. Always confirm critical parts with a trial bend.
Using the Sheet Yield Estimate
The sheet yield section compares normal and rotated nesting. It estimates how many blanks fit on one stock sheet. It also estimates sheets needed for your quantity. This is a rectangular nesting estimate. It does not replace full nesting software. Still, it gives a fast material planning check. Use a realistic nesting gap. Include clamp zones when your cutter needs them.
FAQs
1. What is minimum blank size?
Minimum blank size is the smallest flat sheet size needed before forming. It includes straight lengths, bend growth, cutting allowances, trims, overlaps, hems, and safety margins.
2. What is bend allowance?
Bend allowance is the developed arc length of the bend zone. It accounts for material stretching around the neutral axis during bending.
3. What is bend deduction?
Bend deduction is subtracted from outside mold line dimensions. It converts finished outside dimensions into the required flat pattern length.
4. Which K-factor should I use?
Many sheet metal jobs start near 0.33. Softer materials, larger radii, and different tooling may need different values. Test bends give better values.
5. Can I use inches?
Yes. Select inches from the unit menu. Keep all length inputs in the same unit for consistent results.
6. Does this replace shop bend tables?
No. Shop bend tables are usually more accurate because they use real tooling, material, and machine behavior. This calculator is best for planning.
7. Why add kerf?
Kerf is the material removed by cutting. Adding kerf helps protect the final blank from becoming undersized after cutting.
8. Why is sheet utilization only an estimate?
The calculator uses simple rectangular nesting. Real nesting may improve yield with part rotation, common-line cutting, grain direction, or irregular shapes.