Drilling Hardened Steel

Another approach would be to try a chainsaw file. They are meant to cut hardened steel and will allow you to move the hole with some control. See if it will cut; if it does, great.
 
I agree with above...Use a cheap masonry bit.. Sharpen it up and go at it on the drill press. I have done this plenty of times and you will get lots of holes out of one bit.
 
If I am correct here he will be breaking into the old hole. this can cause masonry bit to bind. Masonry bits hate that type of drilling. Diamond burrs seem as if they will work.
cdhknives, how did you harden it the first time? Send it out?
 
The blade was heat treated by a professional bladesmith. I'm just a hobbyist...I let the pros handle heat treating high end stainless steels...1900F for 1 hour, controlled quench, tempering 3 times for 1 hour each, liquid N2 cryo after first temper, etc. Not for my half dozen blades a year!

I tried to plunge a 1/4" carbide mill but it chipped the cutting edges. Then I tried a 3/8" 4 flute ball end mill and it cut very nicely...once I tightened up my spindle preload collar. I just replaced bearings and I'm thinking the rear bearing race didn't seat fully. Grrrrr.....:mad:

End result:
20150613_155336_zps7x5hsx2t.jpg
 
There may be a way to locally anneal the area. Many years ago I had a similar problem and had read somewhere that using the head of a nail to anneal a small area can work. I clamped the blade I was drilling to the drill press table and brought the head of a 16-penny nail into contact with the metal. I ran the drill press at high speed and used a fair amount of pressure and the area under the nail head got red hot. I let it cool naturally and drilled through without a problem. It didn't seem to affect the hardness of the rest of the blade. Now, this was over 20 years ago and I'm going from memory so the details are getting dimmer but the general process is right. If you try it, maybe do it on an old spare blade first?

Oops, you just posted the photo above - too late!
 
As mikey just suggested a local area can be annealed.
Use DC current. If you use a battery charger there must be a resistor ( or light bulb ) in line to keep from letting the smoke out.
Use carbon electrodes either side of the area to be annealed and heat it up.
Not tried this myself but heard of it years ago.
 
CD nice job. I was wondering about the heat treating. I stop at w/o-1 after that it is over my head, and the equipment to high priced. Never sent any thing out is it pricey as I would think.
Mark
 
A chainsaw file isn't ever going to cut hardened steel. Chainsaw blades aren't very hard. I doubt they are even up to 52 RC,which is the hardness of a good spring steel. That is fileable,but starting to get hard on the file. Soon wears a groove in a triangular file when filing saw teeth sharp.

I drill holes through all manner of hardened steel-even fully hard files and full hard HSS power hacksaw blades. I just use inexpensive masonry bits run as fast as a regular drill press will go. It heats up the steel yellow hot and scoops it out as it drills.

You will sometimes melt the brazing that holds the carbide tip in,so let the drill cool a little intermittently.
 
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