Is there a design flaw with the blade holder jig for sharpening jointer blades ? I am trying to sharpen 5/8 inch wide blades (supposed to be able to sharpen minimum 1/2 inch width blades ) at a 30 degree angle, and when I try to sharpen, the blade holder scrapes on the grinding wheel before the edge is sharpened even close. My grinding wheel is not that old, only worn down about 3/8 inch from original diam.