How does a spade bit work?
Spade bits are among the most simply designed drill bits in that they are flat, with sharp edges on opposite sides.
When you drill a hole with a spade bit, the first part of it to touch the wood is the centre point. This sharp point keeps the bit from skipping around while it bores a hole.
If the spade bit has spurs, these are the next to get to work, scoring around the edge of the hole and effectively cutting it from the outside in.
The lips are the last to engage, and they cut material from the bottom of the hole. When it comes to removing waste material, the lips do the majority of the work.