Soft top jaws can solve many gripping tasks for turning operations applied to standard power chucks. Soft jaws are more versatile than you might expect, but it takes experience and sometimes expert advice to apply them effectively.
By Paul Fowler
Some turned parts are just tough to grip. They aren\'t round. They deflect. Their surfaces are irregular or inconsistent, and sometimes a combination of these conditions. The features to be turned or bored may not be centred on the workpiece. These and many other workholding challenges can be solved quite nicely with standard or specially made soft jaws.
Why soft jaws
Soft jaws are commonly used for second operation work on previously machined surfaces to prevent part marring and for improved concentricity. Soft jaws are generally machined to size, in position on chuck or formed into the desired shape for holding difficult shaped work pieces. In contrast hard jaws are best suited to first operation gripping of black bar.
Soft jaws offer the following advantages as compared to hard jaws:
- Ideal to grip pre-turned bar as they leave no clamping marks
- Provide very good concentricity as they are typically bored out on the machine
- Provide flexibility for awkward-to-grip parts where irregular surfaces may be present
- After forming the soft jaws they can be flame hardened (in the case of Dimac jaws that are made using 1040 carbon steel) to minimises wear.
- Custom soft jaws can be made to wrap around the work piece to minimise work piece deflection or distortion
- Carbide gripper pads can be fitted to custom soft jaws for gripping forgings and castings
- Balancing of unsymmetrical workpieces can sometimes be achieved by varying the amount of material left on each soft jaw
- Soft jaws come in a big variety of sizes allowing gripping of parts that would not be possible with hard jaws such as very small or large diameters
Soft Jaw Types and Selection
Soft jaws should conform to an industry standard to fit master jaws that may have fine or course metric serrations, or the much less popular, fine or course inch serrations. Manual chucks typically have tongue and groove type cross tenon mount. It is critical to choose the correct serrations, slot width and centre hole distance to suit your CNC power chuck. The most common metric size is ......