Hydraulic chucks are very common workholding devices – especially on CNC turning centers. They provide a tremendous mechanical advantage. That is, a relatively small amount of input pressure results in a huge amount of clamping pressure at the jaw.
For this reason, it can be difficult to determine with the standard chuck pressure gauge that is equipped on most turning centers to tell just how much force is being exerted on the workpiece. This is because the chuck pressure gauge measures the input pressure going to the chuck – and is not very helpful for determining accurate chucking pressure at the jaw. For this reason, many CNC users tend to crank up the chuck pressure valve just to be sure they have enough pressure, which of course, can place undue wear and tear on the chuck.
This coupled with not following the chuck manufacturer’s recommendations for grease and/or other lubrications can lead to a decrease in chucking pressure. But unfortunately, if you don’t know (accurately) how much pressure you’ve been applying to the jaw, you’ll never know when this pressure drops.
The only way to accurately know is to use a chuck pressure gage that measures pressure at the jaw. These devices are available from tooling or chuck manufacturers and should be part of every setup. Again, if you don’t know how much pressure you’re exerting, you won’t know when wear and tear on the chuck cause it to decrease. This can lead to a very dangerous situation.