I ordered the two pack of step bits from Bobby, which includes the small one (3/16" to 7/8")and the larger one (13/16" to 1 3/8"). Need the bigger one for my heating elements. I'm not sure how well they are going to hold up being relatively inexpensive bits.....not Greenlee's. With my HERMs system I will have a total of 12 holes to drill or punch. I will have 7 bulkheads combined in the three vessels, 2 site glass ports, a temp. probe port in the BK, and two larger holes for the heating elements (one in the HLT and one in the BK). If the bits don't hold up, I have a set of Greenlee punches that a patient of mine is letting me burrow, but it appears at first glance that they are conduit punches. Looks like I could punch the 7/8" holes for the bulkheads, but that's about with his set.
I think that I would rather drill initially, because I would hate to have a bolt snap or ruin the die on one of his punches. Greenlee punches are ridiculously expensive, so I'm reluctant about using them despite the fact that they punch a nice cleaner hole than drilling. I think I'm going to take Bobby's advice and drill slow, with moderate pressure under high torque, with plenty of cutting oil and see how it goes. I'll start with the small bit and knock out the 9/16" holes for the two site glass ports and the temp. probe port first. Then I will use the larger bit to drill the 1 1/4" hole for the heating elements. Then I will switch back to the small bit and start drilling the 7/8" bulkhead holes until it fails, at which point I'll try to use the larger bit to finish the rest of them. If both bits fail before then, I'll resort to the punches.