I regularly make similar tensile specimens out of ¾” steel and aluminum bar stock. The gage section of the specimens is turned down to ½”. I make them on a Warner & Swasey turret lathe. The tooling used is a Kennametal tool holder with ½” round insert. The round tool is used to make all cuts in the gage section of the part. The profile cut is made in 3 passes two .050” ruffling pass and one .025 finish pass. Each pass starts at the right hand side of the part and then plunges in, then cuts towards the head of the machine. The machine Is old, so the spindle speeds are low in my case (750 rpm) and the surface finish would probably be better if cut at a faster speed. But in all of my trials with these parts I have found that cutting the profile in one motion is best, because if there is any step or mark from using two different tools to cut the radius and the gage section it will result in a stress point that can throw off the tensile testing.