Make sure that you smith all items AFTER receiving the task from Doric. Doing it beforehand will not count, thus you will be required to make them again.

1. Return to Doric and ask if he has any more tasks for you to do. He will ask if you want to help take the fight to the Trolls. Exclaiming your interest, he will inform you that Commander Denulth is looking to lead another assault on the Trolls. You will then be asked to make 2 Steel chainbodies and be handed a Task list.
   
   
2. Create the 2 items (this will use all 10 Steel bars) then teleport to Burthorpe. You will find Commander Denulth East of Burthorpe Castle.
   
   
   
   
3. When talking to Commander Denulth, a soldier will report to him that a Troll has taken out one of the cannons. You will need to return to Doric to learn how to make a Cannon part.
   
   
4. Make the cannon part on his anvil before returning to Burthorpe - Note that the Bronze bars must be in your inventory, they will not work from your Metal bank.
   
   
5. Teleport to Burthorpe and instead of running East to the Commander, go North into the castle. Climb the stairs in the North East corner, then the steps in the South East corner to reach the roof. Repair the middle cannon along the North wall of the building and return to Commander Denulth.
   
   
6. Inform him that the cannon has been fixed and you will receive 500 Smithing experience and 1,500 charges on your Gofannon amulet.