using 70-X Tapmatic with 5/8 tap on radial arm drill

I set up my radial arm drill with a 70-x Tapmatic threading attachment. I am using a 5/8"-11 tap going through 3 layers of steel totaling 1" in depth. The tapping tool came with a #3 jacobs taper I am using a no 4 morse taper for quick change. I have the speed set to 60 RPM. I used to do all the tapping by hand, this cuts the time down and cuts the threads more accurately.