Quetzalcoatl.Kenrusai said:
»You may or may not know this already, but when griding dragonforged equips, try and have the piece(s) at level three. This'll give you a 15% chance of upgrade from Wyverns, 18% from Drakes and 20% from the Wyrm in the everfall. Additionally, the offline Ur-Dragon gives you a 50% chance, while the Online Ur-Dragon will gurantee a dragonforged piece. Those listed dragons will only dragonforge one piece at a time, as opposed to "The Dragon" in the main story quest, that will dragonforge all current equipped items upon defeat.
That's not -entirely- accurate. There is still a lot of speculation about forge rates on the forums but the consensus atm is that level 0 gear has a 0% chance and level 3 gear has the highest chance.
Drakes, or more specifically the one near the shadow fort, have the lowest forge rate, but are the only dragons to respawn before post-game. The respawn time is 7 days. It can forge multiple pieces of gear, or none at all. The best way to farm it is to wittle it down to 1 HP, since the Arisen has to land the killshot on the heart, this is easy. Then run out of range and save, then you just have to one shot the drake, and if nothing is forged reload. Rinse and repeat. There is a camp nearby that you can rest for 7 days and forge gear until your heart is content.
Just personal experience, but I find that gear has a higher chance if you have less gear equipped. It seems to not roll on empty slots, or at least not roll on slots that may already be forged.