Handle Hole
Why do you need a hole 7" deep? Most any tool handle I've ever made, some for square carbide tool shafts, has only needed a hole 2-2.5" deep. Installing a metal ferrule on the end of the tool handle around the hole (with at least 1/4-3/8" of wood around the hole) will help keep it from splitting for most uses. A short length of copper pipe works fine as a ferrule.
I'd also round off the square shaft (on a grinder) where it is going into the handle (and then you only need a 1/2" hole for 1/2" square stock), size the hole diameter so the shaft slides in smoothly with a little pressure, but not loose, then use epoxy when gluing the shaft into the handle. Filing a groove or two in the round portion of the shaft going into the handle will help keep it from turning in the hole after the epoxy sets, but not really necessary.
I think rounding the shaft where it goes into the handle will provide a stronger tool overall as more of the tool shaft will be directly supported by the wood around it instead of just being held by the epoxy. Has always worked for me and haven't split a handle yet even with some pretty nasty catches. Good Luck and have fun!