A single-actuator linkage that grips round stock dead-center, every time.

What it is

This is a SolidWorks design for a self-centering steady rest — a clamping mechanism built to support and hold cylindrical parts (shafts, tubes, round bar stock) perfectly centered while they're being machined, welded, or handled. If you've ever needed a long thin shaft to stop whipping around on a lathe, or a robotic cell to grab a round part without it landing off-axis, this is the kind of mechanism that solves it.

The whole design is driven by a single pneumatic/hydraulic cylinder — no need for two separate actuators or any electronic syncing. One push does the work.

How it works

Push the cylinder rod up, and it drives a central "spider" pusher straight up the middle of the mechanism. That pusher is linked to a pair of mirrored rocker arms, which in turn drive two curved jaw arms outward and closed. Because both jaw arms share the same central pusher, they're mechanically forced to move by exactly the same amount at the same time — so the part being clamped always lands on the true centerline, no matter which side it leans toward when it drops in. That's the "self-centering" part: it's built into the geometry, not into a control system.

The whole assembly bolts to a mounting plate with a full pattern of fixing holes, so it's ready to be dropped into a larger fixture, machine frame, or automation cell.

Why it's a good one to study or build from

• Single-input, dual-output linkage — a clean example of converting one linear motion into two synchronized, symmetric motions purely through mechanical geometry.

• True self-centering, not just self-adjusting — the jaws are kinematically coupled, so centering accuracy doesn't depend on equal friction, equal spring force, or careful tuning.

• Fully constrained SolidWorks assembly — every link, pivot, and pin is mated and moves correctly when you drag the actuator, so you can actually see the kinematics work, not just look at a static shape.

• Real-world application — this is the same working principle used in lathe steady rests, centering fixtures, and self-centering grippers, so it's a great reference if you're designing something similar or just want to understand how these mechanisms are built.

What's included

• Native SolidWorks files (.SLDPRT for every part, .SLDASM for the full assembly, fully mated and drivable)

• Neutral STEP file of the complete assembly, so you can open it in any CAD software even if you don't have SolidWorks

Good for

Mechanical engineering students studying linkages and kinematics, makers and hobbyists building fixtures or automation rigs, and anyone who wants a working reference for a self-centering clamp mechanism instead of designing one from scratch.