I think that you should make your holding jig deeper so that your fingers are not inline with your cutter. When i was much, much, much younger I made a jig simlilar to yours using a milling cutter and my drill press to rout a recess' for hand mirrors. The handles were too close to the cuttter path, the cutter caught the material and jerked my thumb into the cutter. Being much, much younger I still had decent reflexes. That being said, I still have four spiral scars in my thumb to remind me to deep my fingers well away from any spinning cutter of any sort.