I have tried to find a thread about this and sorry if I overlooked. I was hoping someone could please tell me how many times I can upgrade a weapon on the grindstone. I thought it was only once, but today I noticed I was able to upgrade my scimitar again to (flawless). How does it work and what is the max amount you can upgrade a single weapon?

It is based on your smithing skill, and can be increased for specific levels of armor/weapons through smithing perks.
Using some potions/enchantments can increase your smithing more, and there is no upper limit if you use alchemy to enhance enchantments to enhance alchemy, etc, to enhance smithing.

The upper level (found using cheats) is beyond the point where an iron dagger deals hundreds of thousands of damage.

So if i drink enough blacksmithing potions can i upgrade it past flawless or would i have had to drink it before that final upgrade, if it is the final upgrade? Sorry still kinda confused

You can only use one potion at a time (You can make better potions than you can find).
While this potion is in effect, your maximum upgrade level is a little bit higher than it was.
Also, one upgrade on any item automatically brings it to the highest upgrade level you can reach at that time.

Thanks I was wondering this as well.

Ohhhhhhh.... Thanks!

So if i have my blacksmithing at 100 and a perk on elevin armor. I would only have to use one refined moonstone to get it to flawless

Yep, although there are levels beyond flawless

Fine
Superior
Exquisite
Flawless
Epic
Legendary

So what specs does my character have to have in order to reach epic and legendary?