I’ve just sorted mine out, I mounted a belt sander in a Work Mate bench and then just ran each corner over it, far easier to control the metal using two hands with the sander held steady. It sands off the corners surprisingly easily and I have no more sharp edges on the corners. I was particularly concerned about people brushing past the fire pit and cutting their legs when there was no fire in it.
You can obviously round the corner off as much as you want but I just did enough to take the sharp edge off so the fire pit looks the same.
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