I am having to drill through the Boron UHSS in a few spots on my build. It's crazy difficult. I have to graduate the hole up to 9.6 MM for rivnuts. I have been doing this by starting very small and using the next drill bit size until I get to 25/64" (9.6 MM).
It takes forever to drill one hole.
I just ordered an 8 MM spot weld bit to see if it will make getting started easier.
Any additional advice is appreciated.
If the hole doesn't have to be precisely located, +-.05" estimate, I would locate the position of the hole, then use a center punch to put a small indentation in the hole-to-be's center.
Next, take a Dremel tool, or high speed pneumatic grinder and put on a 1/4" high speed ball-end carbide steel bit. (Not the crappy ones that come in a Dremel took kit
.) Grind the bit carefully into center punch indentation and grind a small hole through, or even 1/2 way into the boron UHSS. The heat that is generated by the bit helps to soften the metal enough to create a starter hole. (Don't everheat the grinding bit by pushing too hard, if you change its color, you have destroyed it.)
Then I use a carbide step drill to gradually enlarge the hole to the size you need. (I recently purchased a high quality 12 step drill bit for about $100.00 ) (Anything that is not carbide will dull down very quickly.)
The other approach if you can't budget or don't want to spend the money on high quality bits, purchase less expensive high speed steel cutting drill bits (Not Hobo Freight Ti Nitride coated crap.) knowing they will go dull and plan on throwing them away or sharpening them and only using them on wood or aluminum in the future.