I've had good luck using "speedbor" flat spade bits. They are boring normal flat bits but there's a cutting tang on the outer edge of both flats, and they work to cut the circumference loose before the main cutting edge lifts the swarf out. [![enter image description here][1]][1] Not a brand recommendation, there are plenty of examples at your average bigbox store. [1]: https://i.sstatic.net/l45gP.png