Drill bits / tough bolts

I'm having trouble getting through my pinch bolts. They seem to be a much harder metal than all the other bolts I've drilled.

I started with this POS Irwin drill bit. Spent about 15 mins on one lousy bolt. Then switched to the milwaukee and it went straight through. Perfect, I found the right bit. But then when I got to the pinch bolt I was getting no where. You can tell it's a lot tougher metal than all the others (it's the bigger one in the pic)

Any strategy to getting through these? It's literally gonna take ~30 mins per bolt of straight drilling at this rate.

I don't know why the milwaukee is so much better, they're both cobalt. I guess that's the best kind?

 

You might have work hardened the hole you started. Pinch bolts are usually 8.8 or 10 hardness. Start with a new drill bit in a new spot on the bolt. If you have a drill press, use it. Believe it or not, I have the best luck with inexpensive black oxide bits that I order from McMaster-Carr. I've done the safety wiring (WERA) on an entire bike with one bit.

 

I was wondering if this was a thing. So while drilling, the metal can I guess "case harden" and become a lot harder to get through?

Would not using oil while drilling cause it to happen?

 

Yes. It's all about heat, so oil can help, but I've drilled really tough metals and accidentally work hardened them simply by not applying enough pressure and overheating the hole. Sometimes you have to slow down the rpms with bigger bits, but little 1/16" bits work best at high speeds, like Dremel speeds, so it's tough. Use steady pressure, good oil like Tap Magic and back off to clear chips to keep the heat down.

 

Learning from the garage journal forum, Dewalt cobalt bits are some of the better bits to use. Also, use oil. I followed this advice and had a much easier time going through the bolts. Oh, and a drill press makes it much easier.

 

I went to the drill toolbox and looked - the bits are Chicago-Latrobe, which is a well respected and very old company that makes excellent tooling. MSC may use them as well.

 

This is a timely thread for me. I've had good success with some Bosch Cobalt bits on my rear axle nut, but struggled yesterday getting through one of the upper triple pinch bolts. Read a little about work hardening, but wasn't sure if that would actually make that big of a difference.

 

Milwaukee HSS are better than their Cobalt bits and better than everything else at HomeDepot/Ace/Lowes/etc for this, IMO.

 

Is that the black oxide one?

 

yep

 

I like to take a file to the bolt area I'm about to drill to knock off the surface hardening.

 

Personally I use carbide bits and proper drill oil, last one I bought was $20 special order. Expensive but they last forever as long as you don't use a hand drill and snap them. I use a press and a jig. Same thing I use to drill cranks and transmissions shafts. Also moving up a few 64ths helps. Plus it makes getting the wire though easier when your an old geezer.

 

I don't know what to do.

I bought some Dewalt black oxide bits. Started a new hole and applied some oil, went about 30% through in less than a minute.... then wouldn't drill any further. Started more new holes and couldn't get anything started. Switched to a new bit and still can't get anything going.


Maybe these are aftermarket pinch bolts that are super hard or something.

 

Most likely you are not applying enough pressure or using too much rpm. 8.8 bolts really are not that hard compared to even HHS bits but can work harden very quickly. Your chips should be silver, once they start to hit yellow you are either to fast or too hard. Blue and you just smoked a bit. Can't tell you the rpm, but what I use is pretty low. I am sure a real machinist will offer some insight soon. I just checked and I use 3/32 bits.

 

Alright I ran to Ace and matched a 12.9 grade bolt to the one off the bike. Went straight through that bitch. The previous owner must have put some crazy hard steel bolts in.

Thanks for all the info. The Dewalt black oxide bit works best.

 

This is 95% of most peoples problem when drilling.

 

I made the mistake of thinking slow was the way to go. Same problem you mentioned. Same bit, same drill at high speed went right through. And oil always.

 

Cool good to hear!
Yeah, they could have been titanium bolts.

My brother in-law was an airplane mech/fabricator and super slow and lots of pressure is the way to go. Also use a coolant when drilling through Ti(oil is better than water if colant is not avail, but tends to smoke), if not within seconds you can hardened them, because they capture the heat and hold it in. If no chips, then feed is not hard enough and the Ti was hardened even further.

 

I use my cordless drill, turn much slower than the corded drill which seems to help.