Need help drilling holes in hardened. (reamer?)

[92lt]

So, first off, I am not a machinist although I have some mechanical experience. So please go easy on me....

I need to drill out the holes on a truetrac differential carrier about 1/16" bigger. It's hardened. I've read it's anywhere from c38 to c60. A hand file does cut into it. I doubt it's c60. I tried a new cobalt drill. No luck. I've read in posts where they suggest using a quality hss reamer.

But if a cobalt drill didn't work, there's no way a hss reamer would cut into it, right? Any suggestions?

 

[FredC]

Was the new cobalt drill a good one? Some pretty junky tools are being passed off as cobalt these days.
What speed was the drill turning? Supported in a machine or with a hand drill? c38 to c60 is quite a range if we are talking about Rockwell "C" hardness.
If the part cuts easily with a file, it cannot be too hard to drill with a good drill high speed drill bit or reamer. Fixtured in a machine with steady feed and support would be better if the part is on the high end of the hardness range.

 

[92lt]

Hmm. It was a new Irwin cobalt bit. So not the best quality I'm sure. Very low speed, hand drill, lubricated. (I have a cheap bench top drill press too, but it spins way too fast even on slowest setting for drilling metal) So maybe just poor drill bit quality then?

Would a Norseman CAR reamer be the correct style (and decent brand) reamer to buy?

Thanks. Learning a lot here

 

[L Vanice]

The size of the existing hole was not mentioned, and that is important in making the best choice of tool to enlarge it "about 1/16". The simplest answer is to use a carbide-tipped reamer with cutting fluid in a good quality drill press or vertical mill, paying attention to the recommended RPM for whatever size the reamer is. A hand tool will not do the job.

For certain size holes, a HS core drill might work, but you still need the cutting fluid and a solid low speed machine tool. For those who are not familiar, a core drill is a special type of drill bit designed for enlarging existing holes.

Larry

 

[durableoreo]

Yeah, you need a rigid setup

1/16 is a pretty big bite for a reamer. A reamer would probably be more rigid than a drill, which is a pro. But in this case, it would be using a reamer like a core drill.

My first though is a piloted counterbore drill but that's probably not handy. I'd try a screw-machine length M42 drill first. If it wanders, you might need a fixture with a hard steel drill guide. Maybe play with chamfers before going nuts on a fixture. If you're ordering tooling, the carbide-tipped reamer sounds like a good option.