Recently I have been making some wood lighted Christmas trees. I carve a .5 inch hole for a countersink area and a smaller hole for the bulb to fit thought. It carves the countersink area fine and when it comes back to carve the smaller holes I hear a grinding like gears skipping a tooth. Then it starts air carving. It messes up my z zero. There isn’t anything blocking it. Its not a belt issue since its a z plus. It does this several times then works fine for a while. I tried to make a cribbage board and it did it again and I lost about .25 off my depth for the holes. Any help or duggestions would be appreciated.