My father in laws partner destroyed their business by working to too close tolerances.The problem with my lathe on those is it's just not beefy enough to knock em out quickly. Also I'm very kind to her and never really push it hard. That taper was done in 3 passes and the tube was originally 1/2" so that was turned down (steadily) then slowly parted off. and although it's plenty good enough to see them to excellent tolerance it's not beefy enough to bash em out quickly. I'd get em down to perhaps 10mins but any quicker on the material with my little lathe and I'm working it harder than Id like to.
Never made any money but turned out super work....+ or - 1 thou is cool unless + or - 10 though is good enough.