by Stefan Gruber
Avoid unsafe clamping issues
Chuck jaws are the only interface between workpiece and chuck, making them a crucial component for increased productivity and efficiency. The use of the right chuck jaw guarantees perfect power transfer and secure part clamping, as well as optimal utilization of the machine and tool capability, increasing machine uptime.
If jaws are not bored correctly, you could face unsafe clamping issues such as run out, suffering repeatability, tool life issues and reduced part quality. Learning how to correctly bore jaws will allow them to last much longer and produce higher quality parts.
One of the most important tips when boring jaws is to choose high quality jaws. This comes down to several different factors including quality of raw materials, quality of design, and quality of manufacture. High quality jaws are proven to last longer, reduce base
jaw wear, and eliminate corrosion. Consistent quality material and precisely ground jaws that have perfect flatness ensure the best fit and finish to your chuck master jaws.
When mounting your jaws, it is important to use the appropriate quality grade bolts and to bolt the jaw down properly with the manufacturer’s recommended torque specs. This ensures maximum jaw rigidity while boring the jaws and clamping the workpiece; a more rigid jaw connection translates to improved jaw life and torque transmission. Another consideration is to locate the jaw in a position that will allow you to bore without interference by the jaw mounting holes. This will ensure maximum clamp depth and full contact area is obtained with the workpiece.
When machining your jaws, bore them at the midstroke of the chuck; this eliminates any difficulties loading the part. Another important step is to bore the jaws at the clamping force used to clamp the actual workpiece using a jaw boring ring or fixture. This ensures the bending moment experienced by the jaws while clamping the workpiece is compensated for and concentricity is preserved. Without this step, the higher the clamping force used, the more stress that is added and the higher the bending moment that can occur, causing unnecessary clamping issues, such as only partial contact of the jaw with part or runout issues.
A relief cut or undercut should be machined in to eliminate the slight radius from the cutting tool at the base of the step of the jaw. This ensures the workpiece remains in place instead of shifting during clamping.
Finally, properly deburr the jaws to assure flatness. Afterwards, when boring the jaws, they should always be paired with the base jaw they were bored on so that loading part repeats against workpiece stop. Mark each jaw with the number found on the base jaw for maximum repeatability when remounted.
When looking for jaws, it is important to have the right quality jaws from the right partner.
Stefan Gruber is in technical sales, Schunk.
