Sheet Metal Bend Allowance & K-Factor Calculator Community
Questions, answers and tips from people who use the Sheet Metal Bend Allowance & K-Factor Calculator. Bend allowance, bend deduction, setback, flat length and K-factor from a test bend.
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This page shows only real posts from real people, so it starts empty. The guide below has the questions people most often have about the Sheet Metal Bend Allowance & K-Factor Calculator. Pick one to start a thread, or write your own.
From the tool guide: common questions about Sheet Metal Bend Allowance & K-Factor Calculator
The items below are not posts by community members. They come from the written guide for this tool and are here to get a conversation started. Use “Ask a follow-up” to open a thread about any of them.
What is the K-factor?
The ratio of the neutral axis distance from the inside surface to the thickness (0 to 0.5).
From the tool guide Ask a follow-upBend allowance vs deduction?
Allowance is the neutral-line length in the bend; deduction is subtracted from the sum of outside legs.
From the tool guide Ask a follow-upWhat angle do I enter?
The angle the material is bent through (90° for a right angle).
From the tool guide Ask a follow-upIs it exact?
It follows the standard formulas; real parts depend on K, which you can calibrate.
From the tool guide Ask a follow-upWhat this tool does
When sheet metal is bent, the inside compresses and the outside stretches, and a neutral line stays the same length. The bend allowance is the length of that neutral line in the bend: BA = θ·(R + K·t), where θ is the bend angle in radians, R the inside radius, t the thickness and K the K-factor (the neutral axis position as a fraction of the thickness). From it follow the bend deduction (BD = 2·OSSB − BA), the outside setback (OSSB = (R + t)·tan(θ/2)) and the flat blank length of a part with several bends.
How to use it, step by step
- Enter thickness, inside radius and angle.
- Use the estimated K or enter your own.
- Build the flat length in the Flat pattern tab.
- Calibrate K with a test bend if tolerances are tight.
Tips from the guide
- Bend a scrap test piece first for critical dimensions.
- Respect the minimum bend radius to avoid cracking.
- Keep flanges longer than about 4 × thickness.
- K-factor depends on tooling and method (air vs bottoming).
Common mistakes to avoid
- Mixing outside and inside dimensions.
- Using 90° when the machine's 'bend angle' means the included angle.
- Assuming one K-factor fits every material and radius.
Who uses it
- Sheet-metal students and designers. Flat-pattern calculations for CAD and drawings.
- Fabricators. Cut blanks accurately before bending.
- Makers with a brake. Calibrate K for their own tooling.
How to ask a question people can answer
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- Say what you tried. List the steps you followed and any settings you changed, so replies do not repeat what you already did.
- Share a small example. A short sample input and the output you saw is worth more than a long description. Remove anything private first.
- Mention your setup. Your device, browser and whether you are on a phone or a computer can explain many odd results.
- One question per thread. Separate topics get clearer answers and are easier to find later with the search box above.
- Come back and reply. If a suggestion worked, say so and upvote it, and if you found the fix yourself, post it for the next person.
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