Note fire grid (was an old bathroom untensils shelf that used to hang in the shower). Not entirely sure if that is needed really, but does work well. Air goes over hot embers before it reaches main fuel wood. Also see semi-final geometry of pie segments of chimney hole. I left four long to stabilise the chimney, and possibly run a screw through them later. So far, I only bent them so the chimney sort of snaps onto them. Works.