I was a Journeyman Machinist working in a job type shop with portable work for many years before I went back to Mech. Eng school
Here's what I have used for additional strength when even a standard key is not enough to hold. You can use a Pin Key as shown on attached link,
Shaft Keys - Types and Their Design
It's shown about 1/2 way down the page.
It's easy to do in-situ with just a couple of drill bits and a hand drill if there is room. A standard straight dowel can be used. It can be drilled as deep as you need for the shear strength required. It may even be tapped and a set screw or bolt installed for additional piece of mind.
The only caveat is that the hub must be flush or close to the end of the shaft and the hub should have some meat on the outside as it introduces different forces into the hub than a standard Woodruff or square key.
For a 1/4" Dowel use a 1/8" or 3/16" drill first and then drill with the 1/4" to depth
, if you use a drill that's been sharpened correctly you will end up with a thous or so clearance on the dowel.
A 1/4" x 1" long dowel has tremendous shear strength.
I have seen bolts/shear pins cross drilled but in my experience unless a tapered dowel is used they always seem to get some slop in the hole with an oscillating loads.
And put your bucket under it to catch the drill chips!