Angle grinder with1mm thick cutting disc is what you want.
This is what I did. Instead of going with the norm and cutting a circle in the top of the keg...I cut around the top weld where the domed top meets the cylindrical sides if that makes sense.
Then used a flap disc and some fine grit sandpaper on the edges to make them smooth enough so I wont slice myself on them.
I did this for two reasons. First one was so I could make a lid out of the top of the keg, and the seam gave me a neat line to follow...this made it much easier to cut a straight line around the top. Second reason, was that I was concerned that if I was to hoist the bag using a pulley or something similar there was a chance I could catch the bag on the edge of the hole and potentially tear it if I cut a section out of the top.
Theres many ways to do it, I find this one worked best in my situation.
This is what I did. Instead of going with the norm and cutting a circle in the top of the keg...I cut around the top weld where the domed top meets the cylindrical sides if that makes sense.
Then used a flap disc and some fine grit sandpaper on the edges to make them smooth enough so I wont slice myself on them.
I did this for two reasons. First one was so I could make a lid out of the top of the keg, and the seam gave me a neat line to follow...this made it much easier to cut a straight line around the top. Second reason, was that I was concerned that if I was to hoist the bag using a pulley or something similar there was a chance I could catch the bag on the edge of the hole and potentially tear it if I cut a section out of the top.
Theres many ways to do it, I find this one worked best in my situation.