Recently I picked up a drivers backrest on ebay. It's a pretty simple design that uses the stock passenger pillion mount.
It's a 3/8" thick x 1 1/2" wide piece of hardened flat-bar, with about a 1 inch slot cut into the end. [See image below]
What I want to do is lengthen the slot [shown in red] by about an inch, so I can slide the backrest further back.
I know there's got to be some sort of drill bit, similar to a router bit, that cuts sideways, but I don't know what it's called. Anyone have any ideas?
Keep in mind, this is a pretty stout metal bar and needs a bit that can handle it.