i should clarify further too..

i am not recommending forstner bits, I am just saying it can be done. I use augers.

On a side not (sort of) I have for a long time been thinking about seeing if I could whip together a dedicated mortise borer. It is not always nice to go for a spin around (or into) a timber!

I have used the half sized hole method before too, it is a good procedure when you are working with some particularly hard to drill wood, like hickory, in which case the torque on a 2" or 1 1/2" bit is very very high.

I've also used the 'mouse ears' method of drilling out the corners with a small bit so that I don't have to clean them out. This only works if the mortise is totally hidden in the joint. It's also a good approach if there is any danger of water getting in the joint, as it can easily drain out. It is a whole lot faster too.