i could drill the hole deeper yes sure. Can I not just use a thin milling cutter and take the corners off
what is a wobble broach? https://www.ebay.co.uk/itm/Broachin...233022929623?_trksid=p2385738.m4383.l4275.c10
Was that what you were trying when you snapped that milling cutter previously? What diameter of cutter would you end up using? As long as the cutter you have has sufficient length on the flutes you probably could. but the 'slot' will always be rounded on the corners, of course.
Mines a through hole. No reason it needs to be blindNo I was milling down large T nut the cutter snapped because it came loose due to me not having a spanner to tighten the arbour. I would use the thinnest cutter I have I guess 4 or 6mm, a slight rounding in the corners should be ok I am making a handle for the machine vice