Reply To: Utter frustration – Auger Bits

Here are a few pictures that might explain how a single spur bit should work. I think those bits are easier to understand.

In the first, the spur is cutting the circumference of the hole. No chips have yet been lifted.

In the second, the cutter is lifting wood. Notice it didn’t remove any wood that wasn’t pre-scored by the spur.

The third picture is at almost a 360° turn. Notice shavings are being lifted by the cutter on the right, but no wood is bein lifted by the spur wing on the left. The bit would bind if it did, because scoring to depth by the spur has not yet occurred there. The binding might strip the snail threads in the wood.

The fourth picture is a two spur bit. The same thing is happening, but twice a turn. Two smaller spiral shavings are being pulled from the hole instead of one large spiral shaving.
Each spur has cut the circumfrence of the hole so the cutter in back of it can lift wood.

I picked bits with about the same snail pitch, so they cut about the same depth each turn.