Self Centering Clamps
A self-centering clamp, or a self-centering vise, is a workholding tool that automatically centers the workpiece, increasing the accuracy and repeatability of the machining process. These tools are also beneficial for milling, drilling, and finishing tasks that need a high degree of accuracy and can be used in either horizontal or vertical equipment, such as mills, lathes, or CNC machines.
Besides a high degree of accuracy and repeatability of the machining process, self-centering clamping systems provide additional benefits, like fast fixturing, higher precision, and increased effectiveness. Of course, as previously said, they can be used on any machine, but they’re especially valuable when used on 4 and 5-axis machining applications.
How do Self-Centering Clamps Work?
The function of self-centering clamps is self-explanatory based on their name alone. To understand how self-centering clamps work, we must break them down into simpler components. Self-centering clamps assemblies consist of a body, an actuation mechanism, and a movable jaw base.
Depending on the type of the self-centering clamp, actuating the mechanism basically move both jaws simultaneously, thus exerting the clamping force equally on both sides. This located your workpiece very precisely and, more importantly, in a repeatable manner.
To do so, movable jaw bases must be equipped with gripping jaws with enough jaw width to ensure proper grip. Most machine vises use either serrated vise jaws or dovetail jaws made of some type of stainless steel. The exception would be inverted circular self-centering clamps, which use special spring mechanisms and external collets to exert clamping force.
Types of Self-Centering Clamps
There are several different variations of self-centering clamps, depending on the application and actuation.
Spindle-type Clamp
A typical self-centering vise — which resembles a typical bench vise — is used for most machining applications. These usually have a spindle mechanism that simultaneously tightens or releases the vise jaws when actuated. Actuation is typically done either by a socket wrench or an Allen key. These are usually mounted to the CNC pallet, drill press vises, or base plates using threaded screws.
Toggle Clamps
Toggle self-centering clamps use a system of levers with two slider-crank mechanisms to clamp or release the workpiece. The conrods and cranks come into toggle by an extension of each other through a parallelogram mechanism that ensures the synchronic rotation of the two cranks. It’s worth noting that actuation can be achieved through automation by using pneumatic pumps.
Tube Clamps
Tube self-centering clams come in a very wide variety, and the selection is based on factors such as the diameter of the tube and the actuation mechanism of the clamp. Expansion blades, internal collets, and spider-type clamps are best used for large and small-diameter tubes, respectively. Spider clamps can even compensate for the ovality defects and accurately centers the tubes for high-precision machining.
Self-Centering Clamps Applications
As we previously stated, self-centering clamps are best used in 4 and 5-axis applications. Most self-centering clamps are of relatively small size (though there are bigger clamps) and feature low-profile jaws, which allows you to keep your tools as short as possible.
This is a massive advantage over typical fixed jaws, as it allows for more room, preventing the spindle head from hitting your clamp or vise. Additionally, in 4 and 5-axis applications, it’s critical to keep the workpiece as close as possible to the center of rotation, and these clamps help you achieve just that.
Summary
As previously stated, self-centering clamps are workholding tools that automatically center the workpiece, increasing the accuracy and repeatability of the machining process. If you’re looking for machining clamps or other workholding tools, check out Reid Supply and their engineering resource guide to learn more about various types of clamps