I too use the pen saver mandrel and occasionally a blank slips. For me this either means I need to tighten it a bit more. 1/8 turn of the handwheel usually does the trick. Or that my tool is too low or dull. If I raise the tool rest, make sure tool is sharp and snug up an extra slight turn, then no problems.and just got the pen mandrel saver from PSI, dont care for that one, good for 1 barrel pens but when turning 2 barrels on the mandrel the barrel closest to the head drive slips alot! no matter how tight you have it.