SteveHGraham wrote:How do you know when you need a bench center?
The requirements set forth by the print will make that determination.
When a guy makes a part on his machine, he's inclined to think it's perfect, that all features are to specifications, but if you've ever used the dials on a machine to establish a dimension, you come to terms with the fact that they aren't always in lock step with what they're told (I trust my dials, but I've had negative experiences).
Surf centers allow for an easy way to inspect a part. They may not be a requirement for the guy who has little talent (not implying you don't), or the guy who doesn't care if a part doesn't comply with the print. Some don't. Surf centers tend to be a QC tool, and may not see much use otherwise. All depends on what you're trying to accomplish. If you must satisfy requirements for other parties (where QC is requirement), you may find them useful. Most folks will never use them, although they may out of curiosity.