Suggestions for drilling through steel-concrete-steel sandwich?

[Digmixfill]

I'm putting a ledger plate on either side of a 9 inch wall. A pair of old railway lines sits exactly where the holes need to be.

I've drilled a few holes using cobalt bits 4->8->10->12mm, then switching to masonry for the centre. Then back to cobalt for the rest of the steel.

The steel is an inch thick or thereabouts, amd It's buggeringly hard too.

 

A mag drill base won't fit inside the web Any suggestions on how to drill these holes quickly?

 

A hole

 

 

The sandwich

[Tennentslager]

Ffs 

Star Trek laser 

[Onoff]

14mm mm masonry bit. Then switch to a 14mm Morse Cobalt hole saw (the best imo, piss all over Bosch) on a 300 mm extension bar. Use cutting paste too. Temaxol, RTD, Trefolex etc.

 

https://www.uktools.com/av10-morse-master-cobalt-bi-metal-holesaw-14mm-916.html

[Digmixfill]

1 hour ago, Tennentslager said:

Ffs 

Star Trek laser 

For the win!

 

1 hour ago, Onoff said:

14mm mm masonry bit. Then switch to a 14mm Morse Cobalt hole saw (the best imo, piss all over Bosch) on a 300 mm extension bar. Use cutting paste too. Temaxol, RTD, Trefolex etc.

 

https://www.uktools.com/av10-morse-master-cobalt-bi-metal-holesaw-14mm-916.html

 

The steel in railway lines is really hard stuff. I had read online, before I started drilling, that trying to work with anything other than carbide tipped tools would end with me spending time dressing/sharpening the tools. That was very true.  I'm sharpening the larger bits after every hole.

Do you think a bi-metal hole saw is up to inch thick hard steel?