In modern engineering and machining, a work-holding system is needed to hold a workpiece in place so that it can be machined or processed. The major types of work-holding system that are applied in the machining operations include clamping vises, fixtures, and jaw chucks. Regardless of the clamping mechanism these devices apply, they all serve to secure the workpiece in a lathe or a machining center when a machining operation is initiated.
The scroll chuck is a type of work-holding system which clamps a workpiece with self-centering (or called self-closing) jaws. Unlike a vacuum chuck or a magnetic chuck which applies atmospheric pressure or magnetic force to clamp a workpiece, the clamping mechanism of a scroll chuck is more identical to that of a vice. The jaws on a scroll chuck are positioned like the claw and it holds the workpiece in place by literally clamping it. Typically speaking, there are three jaws on a scroll chuck; that said, there are scroll chucks with more jaws available on the market as well.
Working Principle of Scroll Chuck
The body of a scroll chuck is a circular, plate-like base. The center of the base is hollow which makes it look like a ring. There are keyways (or called key slots) crossing from the outskirt of the ring to the hollow center of the base. The keyways are the grooves for the jaws to be centered (to close). There are three key ways on a three-jaw scroll chuck, four keyways on a four-jaw scroll chuck, and so forth.
The jaws on a scroll chuck are made of two pieces: the bottom jaw and the top jaw. There is a part called rack on the bottom jaws; the chuck base engages the rack and scrolls the jaws at the same time to open or close the jaws. The bottom jaws and the top jaws are interlocked, so when the bottom jaws close, the top jaws close too. The top jaws are the parts that clamp a workpiece.
The jaws on the scroll chuck are sometimes called dogs. The number of jaws (or dogs) on a scroll chuck determines what kind of materials it can clamp the best. With more jaws, a chuck is considered more powerful to secure the workpiece. For example, a four-jaw scroll chuck provides an easy clamp to a square piece; however, it is more likely to mar the workpiece with more jaws. Just like the vices, the jaws of a scroll chuck can be made with different materials and designs to hold different pieces.
The Use of Scroll Chuck
The properties of a scroll chuck and vice are alike in many ways. The configuration of scroll chucks is a bit more complicated than vices but the clamping approach is similar. They both clamp a workpiece by closing the jaws together. However, what makes them substantially different is the clamping mechanism as well. A scroll chuck is an ideal option for bowl turning. In a bowl turning process, a scroll chuck clamps a workpiece by opening the jaws instead of closing them. The opened jaws push firmly against the bowl recess to its bottom so that the bowl is secured.
Besides, the opening and close of the jaws on a conventional scroll chuck are made in unison. To be exact, the movement of each jaw is synchronized and the force each jaw is able to deliver is the same as well. The advancement of a modern scroll chuck makes it possible for the jaws to have a different degree of opening and closing for the chuck to fit as many measurements for work as possible. For the processes that involve bowl-turning, the four-jaw scroll chucks are the most preferable. The four-jaw scroll chuck is suitable for most measurements for work holding. The four-jaw design also provides the best clamping to both round and square workpieces.
A scroll chuck is useful not only in bowl turning operations but also in lathe machining operations. It has been incorporated as a part of the CNC machining center in the manufacturing industry nowadays and has further developed into different subtypes to meet more requirements in the tooling and machining to date.
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