Knuckle Joint Press vs Eccentric Press
A knuckle joint press multiplies force sharply and slows the slide near bottom dead centre; an eccentric press has more even slide motion and a less pronounced force peak. Choose knuckle joint for coining, sizing and calibration; choose eccentric for high-volume blanking, piercing and general sheet metal stamping. Current TRIGA availability differs by category, so check listings before specifying the machine type.
Published: 13 Jul 2026 · Updated: 30 Jul 2026
At a Glance
| Criteria | Knuckle Joint | Eccentric |
|---|---|---|
| Force curve near BDC | Multiplies sharply, up to 10:1 or higher as the linkage nears straight alignment | Flatter, more predictable peak; close-to-sinusoidal motion through the stroke |
| Slide speed at BDC | Drops sharply, with an extended dwell at near-maximum force | Continues at moderate speed, no dwell period |
| Typical stroke rate | Roughly 16-50 spm on heavy knuckle joint presses | 20-200 spm |
| Best suited to | Coining, sizing, calibration, deep drawing of complex geometries, cold forging of work-hardening or high-strength alloys | Blanking, piercing, bending, shallow drawing, progressive-die stamping, general sheet metal stamping |
| Overload protection | Critical: a wrong shut height or oversized blank can overload the frame and tooling quickly | Still required, but the force rise is less abrupt |
| Dimensional control | Extended dwell reduces springback and improves dimensional accuracy | Driven more by fixed stroke geometry than by dwell time |
| TRIGA current availability | Barnaul, TMP Voronezh, Agostino Colombo and Kieserling & Albrecht, 400-2500 ton | No separate active category; ZTS Smeral LE 400 C is a sold reference; eccentric (crank) drive also appears in TRIGA's hot forging sourcing history (Massey, SMS Eumuco, TMP Voronezh) |
How Does a Knuckle Joint Press Work?
Toggle linkage
A knuckle joint press uses a toggle or knuckle-link mechanism between the crank and the slide. The linkage changes its mechanical advantage as the slide approaches bottom dead centre.
Rising force near BDC
A 10:1 or higher multiplication of drive force is possible close to bottom dead centre, where the linkage is almost straight and forming pressure rises very sharply.
Very low final speed
Slide speed drops strongly at the end of the stroke. That low final speed helps the die apply high pressure without a fast impact at the moment of sizing, and the mechanism can sustain near-maximum force through an extended dwell at bottom dead centre.
Precision forming work
This behaviour suits coining, cold forging, sizing and calibration, where high pressure and dimensional repeatability matter more than maximum stroke rate. The extended dwell gives material more time to flow into die cavities, reducing springback and improving dimensional accuracy.
How Does an Eccentric Press Work?
Eccentric or crank drive
An eccentric press uses an eccentric shaft or crank mechanism to convert flywheel rotation into a fixed slide stroke. The flywheel stores energy between strokes, so the drive motor draws power mainly during the forming portion of each cycle.
More even slide motion
Compared with a knuckle joint press, slide speed follows a close-to-sinusoidal curve: it peaks near mid-stroke and decelerates approaching bottom dead centre.
Higher cyclic output
Eccentric presses are often selected where strokes per minute and repeatable cycling are the main production drivers. 20-200 strokes per minute is the typical eccentric press speed range, compared with about 16-50 spm for heavy knuckle joint and hot-forging presses.
Stamping and forging uses
They are common for blanking, piercing and general stamping. Eccentric-drive presses also appear in hot forging lines for open-die and closed-die work.
How Do Force Curve and Die Protection Differ?
Different force curves
A knuckle joint press concentrates its highest usable force very close to bottom dead centre. An eccentric press has a less pronounced peak and a more predictable force profile through the stroke.
Knuckle overload risk
Because the toggle mechanism amplifies force sharply near bottom dead centre, overload protection is critical. A wrong shut height or oversized blank can load the frame and tooling very quickly.
Eccentric behaviour
An eccentric press is still a mechanical press and still needs protection, but its force rise is less abrupt than a knuckle joint press at the final part of the stroke.
Tooling consequences
Coining and calibration dies benefit from the slow, high-pressure finish of a knuckle press. Stamping dies often benefit from the more uniform motion and faster cycling of an eccentric press.
What Are the Typical Applications?
Knuckle joint applications
Knuckle joint presses are used for coining, sizing, calibration, deep drawing of complex geometries and cold forging of fasteners, bearing components, precision steel parts and work-hardening or high-strength alloys.
TRIGA knuckle catalogue
TRIGA's active knuckle joint catalogue currently includes Barnaul (including the 1000 ton K8340), TMP Voronezh, Agostino Colombo and Kieserling & Albrecht machines in the 400-2500 ton range, subject to current availability.
Eccentric applications
Eccentric presses are used for blanking, piercing, bending, shallow drawing, progressive-die stamping and general sheet metal stamping where repeatable motion and higher cyclic output are valuable.
Hot forging drive type
Eccentric (crank) drive is also common in hot forging. TRIGA's hot forging sourcing history includes Massey and SMS Eumuco, both mechanical crank presses now sold, and the active TMP Voronezh K8542.
Frequently Asked Questions
Yes. Both terms describe the same drive mechanism. "Toggle press" is the common US term for a knuckle-joint press, which is why these presses suit coining and sizing work.
A knuckle joint press multiplies force sharply near bottom dead centre and slows the slide at the end of the stroke. An eccentric press has a more even slide motion and a less pronounced force peak.
A knuckle joint press is usually the better fit because coining, sizing and calibration need high pressure and controlled low slide speed near bottom dead centre.
An eccentric press is usually faster for blanking, piercing and general sheet metal stamping, where the process benefits from higher strokes per minute and repeatable fixed-stroke motion.
TRIGA does not currently list a separate active eccentric press category. The ZTS Smeral LE 400 C eccentric press is a sold reference. TRIGA's active knuckle joint catalogue currently includes Barnaul, TMP Voronezh, Agostino Colombo and Kieserling & Albrecht, and eccentric-drive machines also appear in hot forging press inventory and sourcing references.
Usually not without rework. Die design, shut height, pressure timing, ejection and overload protection must be checked against the different kinematics of a knuckle joint press and an eccentric press.
A 10:1 or higher force multiplication is possible near bottom dead centre as the toggle linkage approaches straight alignment. This is also why shut height accuracy and overload protection matter more on this press type than on presses with a flatter force curve.
20-200 strokes per minute is the typical speed range for eccentric presses, compared with about 16-50 spm for heavy knuckle joint presses. The trade-off is the flatter, more predictable eccentric force curve versus the sharp knuckle-joint bottom-dead-centre peak.
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