There are hundreds, maybe thousands, of articles on the web about the differences between a hobby and a business. Legally, you are required to pay taxes on any profits you make in any activity. The difference in the IRS perspective really comes down to deducting losses and depreciating assets. That is when they will exercise a litmus test to determine if you have a hobby or a business by their definition.
There are activities in some hobbies that require licensing. Hobby farming comes to mind; you don't need a license to be a hobby farmer but you may need a license to spray certain chemicals or buy/administer certain vaccines for livestock. Knifemaking as a hobby may not require any license but that doesn't mean that you are not bound to the local laws for selling, transporting, distributing certain kinds of knives.
Your last post makes it sound like you are intending to make money at knifemaking at some point. When you begin to streamline your processes, manufacture in quantity, and buy in bulk, you will need to start looking at business licensing as required for your area.
Bob