Somebody mentioned about chipped bits. I am not familiar with the bit of a comm lathe but on a normal lathe the bit is shaped for different materials or how much material you intend on taking off in one pass. It is also shaped to direct the swarf.
When i chip a bit on a normal lathe and make a pass it will tend to leave drag marks on the workpeice. Its as if the tip is heating up too much. But its certainly no where near as clean a cut as a new unchipped bit. Whether this is the same on comm lathe bits i dont know..