Here is a picture of my full size keg that I am in the process of converting to a keggle.
I have already cut the hole in the top and I am in the process of polishing it.
I used the same angle grinder that I used to cut the hole in the top, to polish the keg up. Of course, I had to get some polishing wheels to use on it.
I do have some cornies that I need to polish as well.
Here is the thread that details the process and equipment needed:
"polishing your keg" is more than a clever euphemism
Although most of those are the big kegs, you can use the same process on the cornies as well!