Okay my character has 100 skill level for smithing, with all the perks unlocked. I improved my dragonscale armors, deadric bow and sword once to the legendary level, but now I can't upgrade it anymore. When I try upgrading, the screen says that I "lack the required skill". I tried it after equiping a neckpiece, a glove and a ring with 'Fortify Smithing' enchantment and I could upgrade it once more but after that I couldn't upgrade it anymore. I know that we can upgrade a weapons and armors even after it reaches 'Legendary' status, so why can't I? Please help!!!

Maybe, just maybe, to upgrade it more you'd need to fortify your skill even higher than the last time you upgraded it?

If thats not the case, maybe beth slapped a sneaky cap on it

I tried it, doesn't work

Okay, so you've upgraded it to legendary, and legendary again, and you need to upgrade it again? How powerful do you need your weapon? I'm in my mid 40s with a Blades sword and a Dwarven Bow I just recently upgraded to legendary (only high 60s skill at the time plus gear) and haven't had too much trouble even with the strongest enemies in the game.

You might want to look up the alchemy/enchantment exploit loop on youtube to make stupidly powerful fortify potions & gear

I've only ever been able to upgrade to legendary once. I'm not exactly sure how to do it again.

But I'm above the armor cap so I don't really care to begin with.

Now drink a fortify smithing potion and try again.

Yeah but with the exploit loop you can potentially enchant a weapon that one shots an elder dragon on master. I don't know how thats fun, but apparently you can do it.

I personally don't think the it was actually intended to improve a weapon past the initial rank of Legendary. Still, once you get to that point, it takes the skill being increased in 40 point increments to improve any further.

Even if you enchanted gear and/or potions, if you do not buff the skill level by an additional 40 points, you will not be able to improve it any further. So, with a skill level of 91 and the perk, you can reach Legendary. Then you need a skill level of...131, 171, 211...

You can also put Fortify Smithing on any piece of apparel for the torso: robes, apron, armor, etc. That would give you a fourth buff instead of just three. Drinking a Fortify Smithing potion while wearing the enchanted gear will provide an additional buff. Equipping the Notched Pickaxe if you have it will give you yet another buff.

As has already been noted, once you have improved something you cannot improve it any further unless your skill increases by the amount necessary to get an additional improvement. If you are already at 100 in Smithing with the necessary perk, the only way to increase your skill is to keep adding additional buffs that stack with each other via enchanted gear and potions, or to sub in new gear/potions that provide a total buff that is more than what you had on the previous trip to the grindstone and also a big enough increase to let you improve the weapon further.