I have my smithing to level 100 but cant make any daedric artifacts past flawless. Same with blades and nightingale

Honestly, no idea. My enchanting makes better weapons that any daedric artifact out there. Now, when I make a character that isn't min/maxed, this will probably not be true.

You might consider making a set of smithing gear if you know the enchantment. That + using potions to buff the skill works wonders for everything that I've tried to improve.

I was wondering about this as well.

I can't get any Daedric artifacts past Epic and my Smithing is 100 with all perks unlocked. Whenever I try to improve them past Epic, it says in the upper left-hand corner of the screen "You do not have the skill required to do that action" or something to that effect.I even have the Dwarven power and tried it using Blacksmithing potions and equipment with Smithing skill enchantment on them.And I still can't improve them any further.
I think that the devs made it so you can't improve them too much and have an uber weapon just to balance out the game.

Find or create the potion for Enchanting. Use that to Enchant Fortify Smithing on the possible pieces of clothing and jewelery. Find or make a Fortify Smithing potion and after donning your Fortify Smithing gear ... drink some.

Smith!

Oh yeah. If you have the Notched Pickaxe ... equip it.

I have the notched pickaxe it does nothing

Smithing works in steps, you raise smithing 13 or something levels and you can upgrade base damage with one on weapons and armor two armor rating.
as you have skills and perks you typical get two more damage for each step, however geting an small skill increase or bonus might not take you to next level.
Now if you don't have the perk for the weapon and many unique items don't have material perks they are twice as hard to upgrade, you can find, buy or make enchanted items with smithing bonus +40% and potions up to 50%. think you need 180 to make everything legendary.
However you can continue to improve items you have perks with past legendary, so they will usually be better if you are an good smith.

It ain't much it's true but when I put on my Blacksmith Apron and all my other fine Smithing gear I feel naked without it.

I just drink the philter of blacksmithing and then upgrade my weapons and armour. Gets them to legendary every single time

Check out this thread:
http://www.gamesas.com/topic/1333470-complete-character-design-freedom-damage-resist-caps-and-ridiculous-damage-thread-9/

From UESP, Legendary (without perk skill needed 168. With perk, 91). I think, even with the appropriate perk, unique items don't quite fall into that catagory. So a Daedric aritifact would need a skill higher than 100 even if you have the perk since it doesn't seem to qualify as daedric as far as the perk goes.

It's because some items are affected by the smithing perk (2x) and some are not.

http://www.uesp.net/wiki/Skyrim:Smithing - this link contains a table describing the relative skill needed to get items to legendary. With the smithing perk you need 91 smithing skill to get an item (of the perk category) to legendary.

But without the perk (or an item that doesn't have a perk, most daedric artefacts) you need 168 smithing skill, which you can achieve through enchanted items or potions.

No. i have a Legendary Daedric Sword. you might have to get your one handed skill higher.

That's absolutely nothing to do with smithing skill, the daedric sword is affected by the 2x perk, which you probably have. Read my above comment if you don't understand.

Oh my bad.