# Press Brake V-Die Opening and Minimum Flange Calculator > Source: https://netray.co/tools/press-brake-die-opening-and-minimum-flange-calculator > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: Free Tools ## Short answer Choose a V-die width by thickness multiplier and check whether your flange is long enough to form without slipping into the die. ## Category manufacturing ## Industry Sheet Metal Fabrication ## Audience - Press brake operator - Fabrication engineer - Programmer ## Tool **Kind:** calculator **Currency:** $ **Inputs:** #### Material thickness **Key:** t **Type:** number **Default:** 3 **Min:** 0.3 **Step:** 0.1 **Unit:** mm #### V-die multiplier **Key:** mult **Type:** select **Default:** 8 **Options:** ##### 6 x t (thin, tight radius) **Value:** 6 ##### 8 x t (general, up to ~3 mm) **Value:** 8 ##### 10 x t (medium plate) **Value:** 10 ##### 12 x t (thick plate) **Value:** 12 **Help:** Common shop rule: 6 to 8 times thickness for thin sheet, 10 to 12 times for thicker plate. #### Air bend radius factor **Key:** rf **Type:** number **Default:** 0.16 **Min:** 0.1 **Max:** 0.25 **Step:** 0.005 **Help:** Inside radius as a fraction of die opening. About 0.15 to 0.17 for mild steel; confirm for your material. #### Minimum flange factor **Key:** mf **Type:** number **Default:** 0.7 **Min:** 0.5 **Max:** 1 **Step:** 0.05 **Help:** Minimum flange as a multiple of die opening. About 0.7 is a common rule of thumb. #### Planned flange length **Key:** flange **Type:** number **Default:** 15 **Min:** 0 **Step:** 0.5 **Unit:** mm **Help:** Measured from the bend line to the edge of the flange. **Outputs:** #### Recommended V-die opening **Key:** v **Expr:** mult * t **Format:** decimal **Primary:** true **Description:** Die opening width in mm. #### Expected inside radius (air bend) **Key:** ri **Expr:** rf * v **Format:** decimal **Description:** Approximate radius formed by air bending in this die. #### Inside radius to thickness ratio **Key:** ratio **Expr:** ri / t **Format:** decimal #### Minimum flange length **Key:** minfl **Expr:** mf * v **Format:** decimal **Primary:** true **Description:** Shorter flanges may slip into the die opening or form unevenly. #### Flange margin **Key:** margin **Expr:** flange - minfl **Format:** decimal **Description:** Positive means the flange clears the minimum; negative means it does not. **Chart:** #### V-die opening and minimum flange vs thickness **Type:** line **X:** t **From:** 0.5 **To:** 10 **Steps:** 20 **Series:** - v - minfl **Disclaimer:** These are shop rules of thumb. Use the die chart from your press brake and tooling supplier for tonnage limits and exact minimum flange values. ## Content **Intro:** Choosing the right V-die opening controls bend radius, required tonnage and the shortest flange you can form. This calculator applies the common multiple-of-thickness rule, then estimates the air bend radius and minimum flange for your part. **Sections:** #### How to use it **Body:** Enter the material thickness and select a die multiplier. For mild steel up to about 3 mm, 8 times thickness is a widely used starting point. Thinner sheet allows a narrower opening and a tighter radius, while thick plate needs a wider opening to avoid excessive tonnage and cracking. Enter your planned flange length to see the margin against the estimated minimum. A negative margin means you should redesign the flange, use a narrower die, or plan a different forming method such as a gooseneck punch or a hem die. #### The rules of thumb used **Body:** In air bending the inside radius is set by the die opening, not the punch tip, and lands at roughly 15 to 17 percent of the opening for mild steel. The minimum flange is commonly taken as about 0.7 times the die opening, because the sheet must bridge the shoulders of the die. Higher strength steel, stainless and aluminium alloys differ, so adjust the two factors after test bends. Results here are estimates for planning and quoting, not a replacement for the tooling manufacturer chart. **Bullets:** - V = multiplier x thickness - Inside radius is about 0.16 x V in mild steel air bending - Minimum flange is about 0.7 x V #### Reading the result and avoiding mistakes **Body:** At 3 mm thickness with an 8 x die the opening is 24 mm, the radius is about 3.8 mm and the minimum flange is about 17 mm. A 15 mm flange then shows a negative margin. Typical mistakes are designing a tight inside radius that the die cannot produce, ignoring the effect of grain direction, and forgetting that a wider die lowers tonnage but increases the minimum flange. Record the die you actually used on the job so the CNC program and the quote stay aligned. **Cta:** We can pull tooling and bend data into your quoting and routing process so engineering notes, die choices and setup times stay consistent across jobs. **Faq:** #### Why is 8 times thickness so common? **Answer:** It balances tonnage, achievable radius and minimum flange for mild steel in the 1 to 3 mm range. Narrower dies raise tonnage and risk marking; wider dies increase radius and the minimum flange length. #### What happens if the flange is shorter than the minimum? **Answer:** The sheet may fall into the die opening, bend unevenly, or lose its position. Options include a narrower die, a special tool, bending before adding other features, or changing the design. #### Does stainless need a different multiplier? **Answer:** Stainless springs back more and is harder, so many shops use a slightly wider opening or add tonnage margin. Check the tooling chart and run a test bend. #### Is the radius estimate exact? **Answer:** No. It is a first estimate. Actual radius depends on material strength, thickness variation, punch nose, and bending method. Measure a sample part. ## Search terms press brake die selection, v die opening calculator, minimum flange length sheet metal, air bending radius calculator, 8 times thickness die rule, press brake minimum flange, die width for sheet metal thickness --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json