Best way to cut 1"+3/8" plate together

[performance]

Again, it's futile whatever you skills are because you have an insulative air gap, ever so small it may be between the two plates. It cannot cut through it, no matter the heat you put into it. Once you cut through the top, you have to essentially preheat the bottom plate all over again. It is nearly impossible to do because of the way the oxyacetylene burns the carbon out of the metal. Once thermal continuity is lost, it won't cut. That's why you can use a torch to "wash" a nut off an axle stud, or a stuck or gaulded bearing off a shaft and NEVER touch the piece underneath. Not so easily done with plasma because the arc is 10k degrees and if electrical continuity is there, its going to cut.

[sticks]

I'm coming in late to this, but if you are still fighting this, I'd spend the $40 on a Champion CT7 plug cutting drill bit. 1" max depth so you would have to probably end up coming up from the bottom, twist drill bit, or use a torch for the last 3/8". Don't need a mag drill, just a good 1/2" hand drill.

Crane mounting holes...you really want to have tight tolerance on those bolt holes unless this is only like a #3k crane.

ETA - I have done multiple layers of oxy cutting. It is a PITA, but if you have a drilled pilot hole that helps. Your top hole will be 3/4 but you will be closer to guesswork on the bottom of the hole due to the nature of the torch flame drift, angle of the torch head...just going to be ugly in general. Not helping that you are doing the 1" first then the 3/8".

[Rambozo]

Another unclean option is to use a cutting electrode with a stick welder. They burn through multiple layers pretty good. But like a torch, a lot depends on the skill of the operator.