Spot drilling case hardened steel

[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]

Originally Posted by mrainey Hey Mike, great minds think alike!

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

[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.

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]

Originally Posted by Zumba Thanks for the replies. I don't need to drill hundreds.... I need to drill thousands.

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]

Originally Posted by 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....

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]

Originally Posted by lakeside 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 ,