What size hole through gear for key to turn aluminum tube?

As you might know, I'm fitting an aluminum tube (6061 .065" wall
thickness) over the gear sticking out of a motor shaft. It fits
perfectly IMO. So now I either glue it or key it (if "key" is the
right terminology). I'm confident that my glue will do the work, but
I'd like to key it to make removing and replacing the aluminum tube
easier.
The motor and its gear have been pressed and glued against a 2 x 4
so that it is secure during drilling.
I need to know what size hole. I plan to drill with a cobalt bit and
then fashion the shank of an inexpensive equal size bit for the key.
I'm planning to go all the way through the gear/shaft/gear so that
the key will stick out from both sides and the aluminum tube will be
torqued on opposite sides.
By the way. Would there be an issue with just drilling a shallow
hole into the motor gear and using a key to turn the aluminum tube
from one side only? Does that throw things off balance? The motor
will be spinning at 5,000 to 10,000 rpm.
The motor shaft diameter is 1/5". The gear diameter is about 1/2".
The gear length is .3".
Should I use a 5/64" or 3/32" drill bit? I might be able to do the
drilling with a smaller 1/16" bit, but is a 1/16" key diameter
big enough to turn the 6061 .065" wall thickness aluminum tube?
Will that drilling risk loosening the gear on the motor shaft?
Thanks.