[Zumba]

I bought a solid carbide spotting drill to get through the tough shell of some case hardened steel shafting - 60rc.

It worked fine in the beginning, but now the bit has dulled after only 20-25 holes. At $25 for the bit, that's $1.00 per hole.... not worth it.

What's happening is that it requires a lot of downforce to get the cutting going. The bit sits there spinning for awhile, not moving down at all. I'm arm is hanging on the quill lever. Then suddenly the quill plunges down a few thou and smokes the bit. That's probably what dulled it in the first place. I have flood coolant going but it just sizzles while the heat builds up.

How much pressure should be required to spot drill hardened steel? I'm thinking about installing a stepper motor on the quill of my mill and running it at something ridiculously slow like .020"/min. I don't have the hand control to move the quill that slowly. Maybe I should use the knee?

In any case, I have to use the BP clone for this operation because some of the shafts I'm drilling are 8ft long. Might be time to convert the manual mill to CNC....

[lakeside]

If you have a die grinder or dremel that you can control use a small round wheel and break threw casing first of course if you have 100s to do this will not be worth the effort

[mrainey]

Maybe you could first grind the case off the spot you're drilling?

[mrainey]

Hey Mike, great minds think alike!

[lakeside]

Hey Mike, great minds think alike!

Your right Mike R, I bet you know what kind of cold beverage I drinking :cheers:

[HuFlungDung]

Try drilling dry, or with a small air blast to clear the drill often. The heat may help to soften the metal to some extent.

From what drilling I have done in hard materials, I find it necessary to resharpen the drill quite frequently. The best point is the split point grind, because this has almost zero web thickness. It is very difficult for the web of the drill to extrude the hardened material.

A diamond grinding wheel is a necessity for redoing carbide drills versus a green SiC wheel which is next to useless, IMO.

[Zumba]

Thanks for the replies. I don't need to drill hundreds.... I need to drill thousands. (chair)

Hence I'll probably need to stick with the carbide spotters. The mill is the only thing I have at the moment with the accuracy and capacity I need.

Huflungdung, I think I'll try resharpening it. I thought about doing it, but wanted to make sure before dropping money on a new grinder. Would you recommend using something like an HF carbide tool grinder or a drill doctor?

[lakeside]

Thanks for the replies. I don't need to drill hundreds.... I need to drill thousands. (chair)

Program a 4 flute carbide end mill to break case harding in one quick pass on Y and the go to spot drill. What size hole are you drill?

[HuFlungDung]

Drill Doctor will not likely work for resharpening unless you get one with a natural diamond grinding wheel, as CBN would be the normal type for HSS drills.

Rather than a carbide spotter, I'm thinking of a die drill, as these have the right point grind on them.

[ajl6549]

I bought a solid carbide spotting drill to get through the tough shell of some case hardened steel shafting - 60rc.

It worked fine in the beginning, but now the bit has dulled after only 20-25 holes. At $25 for the bit, that's $1.00 per hole.... not worth it.

What's happening is that it requires a lot of downforce to get the cutting going. The bit sits there spinning for awhile, not moving down at all. I'm arm is hanging on the quill lever. Then suddenly the quill plunges down a few thou and smokes the bit. That's probably what dulled it in the first place. I have flood coolant going but it just sizzles while the heat builds up.

How much pressure should be required to spot drill hardened steel? I'm thinking about installing a stepper motor on the quill of my mill and running it at something ridiculously slow like .020"/min. I don't have the hand control to move the quill that slowly. Maybe I should use the knee?

In any case, I have to use the BP clone for this operation because some of the shafts I'm drilling are 8ft long. Might be time to convert the manual mill to CNC....

how many pieces? how fast spindle etc.

[M-man]

Use a hydralic toolholder to get the drill runout to be as close to zero as possible.. (0.01mm) runout takes about 50% of tool life, 0.02 takes a lot more and so on... And make sure u use the recomanded speeds and feeds.

[dertsap]

Program a 4 flute carbide end mill to break case harding in one quick pass on Y and the go to spot drill. What size hole are you drill?

i agree , but peck drill it dry with a light peck and feed , similar to what you would do to burn out a broken tap
use some older burned out carb endmills ,stubbier the better, regrind them as needed
then it won t hurt the pocket book so much ,

[Zumba]

The problem is that the case hardening goes down as deep as .150". I tried a 3/8" carbide endmill on a piece of scrap and the flat that it created when going down that deep was too wide.

I think my only hope is to constantly resharpen the spotter dril. I will also use a collet instead of a drill chuck to minimize runout.

[lakeside]

what size hole are you drilling could you sprial down the .15 with a center cutting endmill undersize first.

[dertsap]

seco makes an insert type counterboring tool , they work unbeleavably well on some hardened stainless we do ,unsure of the exact hardness but it is tough material and an interupted cut as well and the tool stands up to it , we can do a lot of parts with one insert , unsure of numbers because those parts are in the production end of the shop ,i ve ran them a few odd times and it is an impressive tool

[SeaSchell]

Staright flute carbide drill, McMaster, MSC, etc. Coated $15.00 or so, Drill at high RPM, Dry with air blast, (not Chiller), Don't over pressure feed at start.

[Derek.C]

A diamond or ceramic tool would be the first tool of choice for myself. Or find a way to break through that case hardening first but it will have to be the entire drill dia otherwise you will have the same problem with your drill getting chewed up. Try a carbide or diamond burr to break thru . Also what is the material and depth of the case.

[HIGHtungsten]

DUde the answer is so simple. heat your steel up to red hot and let it cool down in sand for a day. this process will soften up the steel.

[stevelang]

cheap masonry bits can go thru case hardened easy.

this is an old post but may be useful to the future search, I read this somewhere and tried, it works great, use masonry drill bits after grinding a little spot with the dremel to get it started and to avoid wooble, it goes like butter, you have to use a drill press and apply some pressure, keep on cooling the bit with alcohol or water spray mist, stop before you go too deep because the masonry bits are not precise, take over drilling with a normal steel drill bit, each masonry bit will last only a couple dozen holes but at a couple of dollars or less each, it might be worth it.

[Newby2]

If you are using a 90 degree spotting drill, a drill doctor will not help
They only grind a 118 and 135 degree drill bit. On the other hand, I have one (drill doctor) that I use at work and the wheel on it works very nicely on solid carbide drills. I resharpen 135 deg. split point SC bits to use in a CNC lathe
Steve