Maybe I'm missing something but if you are trying to get through some kind of metal before you hit the concrete then you can't use a masonry bit first. I had this same issue but my beam was square metal box incased and filled with concrete so I used a regular carbide tip bit at low speed to get me through the metal then the masonry bit to finish the hole. I used tap-cons to mount my shades and complete the job.
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Philadelphia, Broomall, Pa, The Villages, Buttonwood
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