Torsion bar vs electro-hydraulic synchronisation
A two-cylinder press brake has one hard problem: keeping the ram level while two cylinders share the load. The industry has two answers — a mechanical shaft and an electronic feedback loop — and the choice shows up in accuracy, price and what happens in year eight.
Side by side
| Torsion bar (WC67K class) | Electro-hydraulic servo (WE67K class) | |
|---|---|---|
| Sync principle | Mechanical shaft forcing both cylinders together | Closed-loop control metering each cylinder independently |
| Feedback | None — the linkage is the correction | Position feedback per cylinder (grating rulers) |
| Accuracy over long beds | Good within rating; more mechanical compliance | Better, and holds it as components wear |
| Programmable crowning | Not typically | Yes — crowning can follow the program and load |
| Components in the load path | Steel shaft and connections | Sensors, servo valves, control loop |
| Main enemy | Wear at the end connections | Contaminated hydraulic oil |
| Cost | Lower | Higher |
What the difference looks like in practice
Bend a long coupon at heavy tonnage and measure the angle at several stations along the bed. On a torsion bar machine within its rating, the gradient will be small and consistent. Push the same machine to the top of its tonnage on a 6 m bed and the mechanical compliance grows — the ends of the bend start to open up. The electro-hydraulic machine measures the difference and corrects for it in real time, which is the entire argument for the servo system.
The crowning guide covers the deflection side of the same question — how much compensation is designed in, and how to verify it with a coupon.
The cost of ownership question
Torsion bar machines are cheap to own because there is little to own: no sensors to drift, no servo valves to clog, no control loop to tune. Electro-hydraulic machines are cheap to own if the oil is clean — the maintenance guide is effectively mandatory reading for owners of servo brakes, because most servo faults we see are oil faults.
Where each one sits in our range
- Torsion bar press brakes — the WC67K range, mechanically synchronised, for straightforward work where durability and price win.
- Electro-hydraulic press brakes — the WE67K range, closed-loop cylinder sync with grating rulers and CNC crowning, for work where the angle has to hold across the bed.
- Electric-hydraulic CNC brakes — servo-driven main pump on top of the closed-loop sync, for energy and accuracy together.
The honest summary
Buy torsion bar when the work is within rating and the budget is real; buy electro-hydraulic when long beds, heavy plate or programmable crowning are part of the job description. Neither is the "better machine" in the abstract — the bed length and the tonnage you actually run decide it. The buyer’s guide walks through turning that into a specification.
Frequently asked questions
What is a torsion bar?
A shaft with twisted ends that links the two cylinders mechanically. As the ram descends, any difference in cylinder travel twists the bar, which forces the lagging cylinder to catch up. It is a purely mechanical, self-correcting linkage — no sensors, no control loop, nothing to program.
What is electro-hydraulic synchronisation?
Position feedback on each cylinder (typically grating rulers) feeding a closed-loop control that meters oil to each cylinder independently. The control keeps the two sides in step electronically, and the same feedback can support programmable crowning and angle correction.
Which is more accurate?
Electro-hydraulic, especially over time and under varying load, because it measures position rather than forcing it mechanically. The practical difference shows on long beds and heavy tonnage, where a mechanical linkage has more compliance.
Which lasts longer?
Torsion bar mechanisms are famously durable: a steel shaft and two end connections, with no electronics in the load path. Electro-hydraulic systems add sensors, servo valves and control loops — more capable, and more components that can drift or fail. Dirty oil is their main enemy.
Which should I buy?
If your work is straightforward bending within the machine's rating and uptime matters more than the last tenth of a degree, torsion bar is the honest, economical choice. If you run heavy plate, long beds, or need programmable crowning and closed-loop angle control, electro-hydraulic earns its premium.
Does the difference show on every part?
No. On short parts in thin material, both methods hold angle fine. The gap opens with bed length, tonnage and off-centre loading — exactly the conditions where you measure the angle at the ends of a long bend.
Ask which sync method fits your work
Send your longest bend and heaviest tonnage. We will tell you which synchronisation method the job needs — and when the simpler one is enough.