i don't normally use carbide on the little lathe as its not worth the cost. i normally kill them on the big lathe doing silly things that they haven't been designed for
the problem is that the big lathe lives somewhere else at the moment as i don't currently have space for it. this means most little jobs get done on the mini lathe but take double the time. the big lathe is a 36ich harrison that can quite easily manage 4mm cuts if i had it wired up on 3 phase. it currently has a 3hp single phase motor in it but i will change it back when it goes in my new workshop that i plan to build after the roadster