[Joey Milia]

While some sort of insert would probably be better design wise I'm just going to comment on the broaching.

I've heard that it's recommend your broaching length doesn't exceed 2x your broaching diameter. So for 1/2 hex 1" would be the edge of that recommended range. However, 192 has done up to 1.5" long 1/2 hex in aluminum belt pulleys for our drivetrain without problems. This is done with cutting fluid on a hydraulic press. If you don't have access to a hydraulic press this may not be possible with an arbor press. There will obviously be higher loads involved as you'll have more teeth engaged at once so be extra careful the broach is kept straight. 6061 is probably the safer bet, softer should be easier to cut.