Did you create the slot for the business cards before or after turning. If after, do you have a jig you use to stabilize the turning? Excellent wood choice and excellent set!
I turned the business card holder to a dome shape, then pushed the tool rest up so that a corner of it was between the jaws of the chuck. That prevented the chuck from turning and I just sawed a slot in the dome and cleaned it up with hand-carving tools and a file. Then I sanded, sealed, and finished.
Now, about that wood envy...
Oh, our time is up for today, we'll have to discuss that next week.