Re: Sinclair case holder wobble
Try chucking the holder in a jawed chuck drill. If it still wobbles then it's the holder.
Otherwise it's the looseness of the slip in holder on the electric screwdriver. MY Black and Decker is a loose wobbly POS for turning. Unfortunately that's why I purchased it.
Either way call Sinclair they're good helpful folks who want you to get the most out of their equipment.
ETA- OH, also check your cases for warped rims. Set them on a peice of glass or small hand mirror or other dead flat hard surface to look for bent rims.