I have a mini mill designed for MT3 taper, I've been trying to figure out if the slot my MT3 tools go into is tapered internally or is just a straight hole (It's hard to tell). What's the standard, can morse tapers mate with normal holes wihout losing concentricity. I wondering because I'm planning on designing a spindle at some point and having it machined in a machine shop. I'm thinking it would be nice if I didn't have to bother with the internal taper but concentricity is paramount. So do I need to design an internal taper?