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Is this as simple as being very careful with an angle grinder? Any brewnosers with the tool for the job willing to give me a hand doing this? The top of the keg is a bit concave, but I am wondering if it could be hammered out flat with a rubber mallet or something before cutting. I use the keg as a fermenter, but the small sanke hole is starting to concern me when cleaning. Corny relief valve also provides a better option for a blow off tube.

The inspiration:

I'm guessing a plasma cutter would be the best tool for that job, an angle grinder might work if you take your time. The plasma cutter would leave you with a much cleaner cut though. I don't think a welding shop would charge much to cut the hole.

It would be tough to get that tight of an oval with an angle grinder. A dremel with a cut off disk might work better but its going to take a while. I would cut it slightly small and then finish it with a grinding stone.

Thanks for the replies. Any recommended welding shops in the city?