I actually made a 'chuck' to hold a 3/8" bolt:
- I took a scrap piece of oak and rounded it off.
- Chucked it into my 4-jaw chuck and drilled a 3/8" hole through it.
- Drilled a 1-1/8" hole about 2/3 of the way through the block.
- Tapped the 1-1/8" hole with my 1-1/4" Beall spindle tap.
- Took the 'new' chuck out of the 4-jaw chuck, removed the 4-jaw chuck from the spindle, then mounted the 'new' chuck on the spindle with the 3/8" bolt sticking out.
The key it to use the proper length bolt to make sure you have a good number of threads sticking out for the plate to screw on to.
I further modified the 'design' by sticking a 1/4" piece of plywood with a 3/8" hole drilled in it on the bolt, rounded it off, and use it as kind of a stabilizing washer. I found that when using the offset holes not all parts of the plate were supported again something. This solved that problem.
Man, I really need to take a picture of this, huh?