Making Money with Weapon Smithing - Kenshi
Weapon Smithing is probably the most profitable crafting profession to raise in Kenshi but it's also the one that will take the longest to pay off. The reason for this is because Weapon Smithing is unlike every other trade skill in Kenshi. In order to make better weapons you'll need to both raise your skill and research ranks of "Basic Weapon Grade" along with other technologies at a Researching Bench. To learn more about researching in Kenshi I recommend my Kenshi Researching Guide, it'll give you a bunch of information to help you understand the basics.
At first you will start out with a plain ol' Weapon Smith which will only allow you to craft items up to Refitted Blade rank. In order for you to craft anything better you'll need to research Weapon Smithing II which allows you to upgrade the forge and craft better items. When you upgrade the forge every weapon you craft from then on will also cost you Fabric along with the Iron Plates. A tip that I use on every play through is stick with a Weapon Smith 1 until you get your smith's skill into the 90s - then upgrade your Weapon Smith to 2.
Eventually you'll be able to make a Weapon Smith III which will allow you to craft items up to Edge Type 2 -- this is the highest quality you can craft a weapon to without mods. Technically you can only craft up to Edge Type 1 at max but if you get a Critical Success then it'll make an Edge Type 2. Also, much like when you upgraded your Weapon Smith to rank 2, upgrading it to rank 3 will increase the amount of reagents that it uses. Instead of Iron Plates and Fabric it will take Steel Bars and Fabric to make weapons.
As far as what weapons should you make to sell - I typically recommend Guardless Katanas since they take up very little inventory space, have a low weight (1kg) and have a high sell price. Guardless Katanas are also one of the best secondary weapons in the game if you plan to use a cutting weapon which is another reason this is a good wep to make. This way any of them that you create and don't want to sell can be used on your team.
In addition to upgrading your Weapon Smith you will also need to research new qualities at the Research Bench to craft better weapons. Advanced Weapon Grades is required to make Mk I - Mk III weapons and Edgewalkers is required to make Edge Type 1 and Edge Type 2 weapons. You will start making a decent profit after you've researched Advanced Weapon Grades and start pumping out Mk I and better weapons regularly. Below you will find a list of the highest quality Guardless Katanas and their sell prices so you can gauge when and how much your profits will be.
Guardless Katana Mk I: 4,375 Cats
Guardless Katana Mk II: 5,090 Cats
Guardless Katana Mk III: 5,752 Cats
Guardless Katana Edge 1: 6,782 Cats
Guardless Katana Edge 2: 7,135 Cats