Blacksmith achievement in Terraria (Xbox 360)

This achievement can take some time and especially if you only craft armors and weapons, by far the best way to achieve this is by crafting a lot of crystal bullets. You only need a crystal shard and musket balls for this. You will have to be in Hard mode for this. If you haven't reached hard mode yet, you can check out my other guide on how to get there:

Musket balls can be bought at the arms NPC for 7 copper a piece, you will need 25 balls to craft 1 pack of crystal balls. The arms dealer will spawn as soon as you have a gun in your inventory and have an empty room ready for him.

Crystal shards can be found anywhere underground as long as its in the hallow, presumably your main house will be on hallow once you reach hard mode so you shouldnt have too much trouble finding some hallow underneath the world. You only need 1 crystal shard for each crystal ball pack.

And of course, as the achievement states, you will need an anvil! And it will have to be a mythril anvil, so you might want to mine cobalt and mythril in hard mode first before you're able to do this.

Further, these crystal balls are also really strong gun ammo so for sure they can be handy for the hard boss fights!