Here are the steps.
I attached the Disk Sander to the accessory quill shaft which I will explain below. I then lifted the SS into the drill press position and chucked a size F metal drill bit. For a 5/16 x 18 tap into aluminum, charts indicate size F is correct.
Remove the original set screw from the casting.
Mark the new bolt location with a Sharpie.
Drill#Bit.jpg
Secure the casting on its side using a bench vice and align the Sharpie mark to the drill bit. Pay attention to rotating the casting in the vice until the drill runs perpendicular to the axis of the channel so the final screw will also.
Then....
