She said she tried a new mat, so that isn't it. I'm wondering if there could be something in the post and hole assembly where the blade goes around. Whenever I change a blade I notice that very fine residue accumulates there and it has to be carefully cleaned out. Also, could there be something wrong with the turn post (axel?) in the middle that is not perfectly round? My dad and hubby both worked with metal tolerances, etc. and I know a flaw in metal might throw off the rotation of the blade.