Vacuum pump question

Well, I finally got the vacuum pump I purchased on ebay up and running. Now for a couple of questions. It is pulling between 18 and 20 inches on the gauge. Is this normal or what should I be looking for. The specs on this particular pump is listed at 26 inches max. I know I'm probably not going to get that, but what is a happy medium? Also, what kind of vacuum is needed to hold a piece on the lathe? Having no experience with this any information would be greatly appreciated.

Also, on another note. Has anyone ever tried using a vacuum setup whenever they soaked their bowl blank in DNA?

Bobby
Louisiana

Bobby, I try to use the bleeder valve and shoot for an average pull of 15 inches. Never had any problems at that setting.;)