Very nice work!
One thing to consider,the weight of the head and speed at which you will turn it,and whether or not 1/2 inch aluminum shank will be rigid enough.
I'm assuming you are making 1/2 inch shank to fit a 1/2 inch holder?
You might consider making the shank as large as your largest holder.
You might also consider having it anodized when finished.
I wish i still had the machine time to make tools like that,but i would be hung from the company sign and stoned.