Making Holes in Frames

[SCOTI]

I've been drilling some holes for my rear airbags & it's a pain in the rear.

I've drilled the 7/16" holes for the bolts that locate the bags but still need to make the larger (much larger) holes for the 1/2" air fittings. The adapters that I'm installing require a hole that's about 7/8".

It's difficult enough drilling upside down for 1/2" holes. A holesaw isn't going to cut it here because there's multiple layers of steel (c-notch plate + original frame + coil spring reinforcement crossmember). I tried some hardware store 'die grinder' tips from Home Depot & they weren't worth the money spent.

What do you guys/gals use to open up holes in metal w/o killing yourself? Where do you get your grinding bits @ that will last long enough to get the job done?