Ask a duct shop what size press brake it needs and the answer usually starts with "I want more tonnage." The honest answer starts with the longest panel you bend and the thinnest die you can live with. Tonnage is a calculation, not a badge number, and getting it wrong cuts both ways: an undersized brake refuses your duct panels, an oversized one quietly taxes you for capacity you never use.
Below is the tonnage math we run with customers, the tooling budget most buyers forget, and the bend-allowance rule that stops blanks from coming out short.
Machine Videos: Factory Tests and Customer Deliveries
See real factory tests and customer deliveries before you buy
The Spec Sheet Question That Matters Most
On a press brake, two numbers decide whether the machine fits your work, and neither is the headline tonnage:
- Bend length. Duct panels are long and thin — 2.5 m bends at 1.0–1.2 mm are daily work. A 160 t / 3.2 m brake does more real duct work than a 250 t / 2.0 m machine, and costs less.
- Throat depth. Return flanges and box sections need the punch to reach past the workpiece. Check throat against your deepest fitting before you compare prices.
- Tooling budget. A brake ships with one punch and one die. Gooseneck punches, hemming sets and radius dies add 8–15% on top of the machine price — plan it before the PO, not after the first job you can't make.
The tonnage table below converts your material and bend length into real numbers, so the "how many tonnes" question stops being a guess.
How to Calculate the Tonnage You Actually Need
Press brake tonnage is not a guess, and it is not the number on the machine badge. It is a function of material thickness, tensile strength, die opening and bend length. Use the standard V-die formula and then apply a safety margin.
Tonnage per metre ≈ 1.42 × tensile strength (N/mm²) × thickness² (mm) ÷ die opening (mm)
For mild steel at 400 N/mm², 1.5 mm thick, with a 12 mm die opening (the common 8× thickness rule): 1.42 × 400 × 2.25 ÷ 12 ≈ 107 tonnes per metre. Bend that across a 2.5 m length and you need roughly 270 tonnes — which is why a 100-tonne brake will happily bend a 300 mm bracket and refuse a 2.5 m duct panel.
| Material / thickness | Tonnes per metre (8× die) | Max bend length on a 100 t brake | Max bend length on a 160 t brake |
|---|---|---|---|
| 0.8 mm galvanized | 30 t/m | 3.0 m | 4.0+ m |
| 1.0 mm galvanized | 47 t/m | 2.1 m | 3.4 m |
| 1.2 mm galvanized | 68 t/m | 1.45 m | 2.3 m |
| 1.5 mm galvanized | 107 t/m | 0.9 m | 1.5 m |
| 2.0 mm mild steel | 190 t/m | 0.5 m | 0.8 m |
Most Shops Over-Buy Tonnage and Under-Buy Length
An HVAC shop rarely bends 2 mm plate. What it does bend is 2.5 m long duct panels at 1.0–1.2 mm. That means bend length and throat depth matter more than peak tonnage. A 160 t / 3.2 m machine will do more real duct work than a 250 t / 2.0 m machine, and it costs less.
Tooling: The Part Most Buyers Forget to Budget For
A press brake arrives with one punch and one die. Everything else — gooseneck punches for return flanges, hemming sets, radius dies, sectionalised tooling — is bought later, usually after someone discovers a job cannot be made. Budget 8–15% of the machine price for tooling up front.
| Tooling type | Use in duct work | Typical cost band |
|---|---|---|
| Standard 88° V-punch | General bending, straight panels | Included |
| Gooseneck punch | Return flanges and box sections without collision | $400 – $900 |
| Hemming set | Safe edges on access panels and doors | $600 – $1,200 |
| Large-radius die set | Curved transitions, architectural duct | $800 – $2,000 |
| Sectionalised tooling | Making up odd lengths without grinding | $1,500 – $4,000 |
| Quick-change clamp | Shops with more than 6 tool changes per shift | $900 – $2,500 |
Crowning: Worth It Above 2.5 m
Under load, a long brake bed deflects in the middle, and the bend angle varies by up to 1.5° across the part. Manual crowning shims correct it; hydraulic or CNC crowning does it automatically per program. If your bend lengths exceed 2.5 m or you hold ±0.5° across the part, spec crowning.
Bend Allowance and Flat Pattern Length
Cutting a blank to the outside dimensions of a finished fitting is the single most common reason a duct panel comes out short. The metal stretches at the neutral axis, so the flat blank must be shorter than the sum of the flange lengths.
Flat length = A + B − bend deduction, where A and B are the outside flange dimensions and the bend deduction for a 90° bend in mild steel is roughly 1.7 × thickness for an 8× die opening.
| Thickness | Inside radius (8× die) | Bend deduction, 90° | Bend deduction, 45° |
|---|---|---|---|
| 0.8 mm | 1.3 mm | 1.4 mm | 0.6 mm |
| 1.0 mm | 1.6 mm | 1.7 mm | 0.7 mm |
| 1.2 mm | 2.0 mm | 2.1 mm | 0.9 mm |
| 1.5 mm | 2.5 mm | 2.6 mm | 1.1 mm |
| 2.0 mm | 3.2 mm | 3.4 mm | 1.4 mm |
Multiply by the number of bends in the part. On a four-sided duct wrap with four 90° bends at 1.0 mm the blank is 6.8 mm shorter than the naive sum — enough to leave a visible gap at the seam.
Ready to Find the Right Machine?
Get a personalized recommendation and factory video demo for CNC Press Brake
View Product Details →Frequently Asked Questions
How long does delivery take?
Standard machines ship within 15-30 days of order confirmation. Custom configurations may take 30-45 days. We provide production progress videos throughout the manufacturing process.
Do you provide installation and training?
Yes. We offer detailed installation manuals, video guides, and optional on-site installation by our engineers. Most customers are fully operational within 3-5 days of receiving the machine.
What about spare parts?
We keep common spare parts in stock and ship them free of charge worldwide. Critical components like PLCs and motors are industry-standard and available locally through our agent network.
Can I see the machine before buying?
Absolutely. We encourage factory visits and can arrange live video inspections. You can also review our 159+ product demonstration videos on our video page.