Passing along method to cut large holes in center of floor skin that I can not get into drill press.
1) Make a Backup plate of 1/8" steel with 1/4"die center hole that is 1" larger in square than diameter of hole.
2) Drill center hole in skin to 1/4" dia. Replace Pilot drill in hole saw with 1/4" drill rod
3) Hold in Backup Plate in place with stacks of Rare Earth Magnets
Another option to make a Backup plate to that can be held with surrounding holes for rivets or anchor nuts if an access plate will cover the hole, match drill rivet holes to the skin prior to cutting the large hole and use Clecos to hold Backup plate in place. I used a 4.5" dia jig to drill pilot holes for access plates riv-nuts and also to drill holes in skin surrounding the 3.5" dia. access holes.
4) Use slow speed to cut hole, the Backup plate with center hole will keep hole saw from chattering and jumping around with thin sheet metal.
I drilled both 5 hole and 6 hole pattern in Jig plate since in some access plates, a 6 hole pattern was needed instead of 5 hole.
For my Yukon build, I ended up with over 12 access holes in my interior floor skins and the drilling jig plate helped speed up the job.
