with a drawbar exactly. can't come loose with a drawbar. i suppose a jacobs taper could come loose just the same but at least just the chuck drops off. and by putting a jt on the spindle it limits the size of the chuck
My dp has a female morse quill with a jt arbor fitted into it for smaller drill bits.
The reason the mill has a drawbar is because the jt or whatever taper would work loose with side cutting forces, whereas in a dp, the force is always pushing the taper connection together. I cant think of a single real milling machine or jig borer not out of china that has a JT spindle...
Pete my (now ex) meddings had a solid quill with a external jt on it. It didn't exactly run true though. Which is why its now my boring bar table and I have a new brown progress after I ventured too near homeandworkshop with some plastic one day