[J_of_Today]

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.

 

[J_of_Today]

I'm using cobalt bits and they aren't cutting it too well. Maybe I fried them?
I started with a 3/16, then went to a 25/64. Still takes forever.

 

[J_of_Today]

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.

They have to be pretty exact because they have to line up for L Track installation. If anything is off, it screws up the whole track. If you make the hole too big the rivnuts won't work.
It's funny, per my last note, I was using Cobalt bits (started small and moved up to the larger bit) and it took hours to drill a couple of holes.
On the next 3 holes, I used a cobalt set from Hobo Freight (love that) and started very small, then just went on up the line until I got to 3/8". This also takes forever but it works. Then I hit it with the 25/64 and I am through.
I can't believe how bad this sucks.

Using these:

135° Split Point Cobalt Drill Bit Set, 29 Piece

Amazing deals on this 29Pc 135° Point Cobalt Drill Bit Set at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

 

[J_of_Today]

Go slow, use lube.

Who's going to say it ...

 

[J_of_Today]

Blair Tools Rotobroaches. They're spendy, but I swear by them. I have the small kit, the large kit, and some spot weld bits. I've used them for years.

https://www.amazon.com/Blair-BLR11091-Diameter-broach-Rotabroach/dp/B005TQWUXU

How well do the spot weld bits work on the boron steel?

 

[J_of_Today]

Thank you all. While I am not drilling 7/8 holes, I am drilling up to 25/64 for rivnuts, so a little over 3/8". This thread and your comments have helped a lot. I've never drilled through so much metal in my life. At this magnitude, you can't afford to destroy the drill bit.
Many rivnuts and two drill bits later, I've gotten a lot better at this ... key has been to slow the RPMs down so much that you can see the drill bit turning and to not push too hard. The bit does the work and the metal spirals or flakes away. When I've nearly punched through I pick up the RPMs to prevent blowouts and the bit from seizing. Blowouts can cause issues seating the rivnuts (only happened to me once so far).
I've not had to drill another hole in the boron steel sections yet, but l when I do, I'll add lube to the bit to keep things going.