How to drill hardened steel

I am a job-shop machinist Calcutta. And forgive me, but I must disagree about needing custom fixtures to grind a drill bit. That is precisely why I did not recommend the straight flute carbide drill, since those have much weaker edges than a spade. If you notice, the actual cutting edge on the spade is negative, while on the straight flute, (or, ironically, due to your inquiry as to whether I was a Tool and Die Maker, Die Drills) the norm is a neutral edge, which is weaker.

I am able to freehand grind my carbide drills with a diamond wheel quite readily, although I probably have a great deal more practice and experience than most here. The only thing I use that could remotely be considered a fixture is a small machinist's protractor to make sure that my cutting edge angles are symmetrical (such can be had new for less than $30 and probably even less on EBay or a similar site. I must admit it may be beyond the ability of some here, but if the exact hole size is unimportant (most freehand ground drills will cut slightly large depending on how close to symmetrical one can get the cutting edges), most should be able to do passably well with a little practice. If a carbide drill can be ground on a green wheel in your estimation, I must admit to being curious why you think a fixture would be necessary to grind one with a much freer cutting diamond wheel?

Cool job. Something different everyday. I'm a machinist in a factory so I get something new everyday too. Helps with the job.

Reasoning behind the fixturing was because you were talking about micro serrations or something along those lines for the need in a diamond wheel for edge retention. So I was assuming you were talking about precision grinding more so than freehand. I don't have a problem with freehand. I do it everyday too. Either wheel will work for the hobbyist. I was just going on the fact that a green wheel is cheaper than a diamond wheel. It's whatever dude wants to buy. If money is no option then by all means get the diamond.

The main reason I would recommend a straight flute drill is they have split points a lot of the time which would reduce the pressure needed to cut, and the neutral rake would take less pressure than the negative rake on a spade drill. It's up to him. I have both and use both quite often. I'd say by now he has it drilled. Lol. I'm sure ten different machinists would take ten different approaches at it. That's just the nature of us. As long as it works then it works.

That tap eroder was basically what I was talking about when I was mentioning an edm sinker. Same concept.
 
Cool job. Something different everyday. I'm a machinist in a factory so I get something new everyday too. Helps with the job.

Reasoning behind the fixturing was because you were talking about micro serrations or something along those lines for the need in a diamond wheel for edge retention. So I was assuming you were talking about precision grinding more so than freehand. I don't have a problem with freehand. I do it everyday too. Either wheel will work for the hobbyist. I was just going on the fact that a green wheel is cheaper than a diamond wheel. It's whatever dude wants to buy. If money is no option then by all means get the diamond.

The main reason I would recommend a straight flute drill is they have split points a lot of the time which would reduce the pressure needed to cut, and the neutral rake would take less pressure than the negative rake on a spade drill. It's up to him. I have both and use both quite often. I'd say by now he has it drilled. Lol. I'm sure ten different machinists would take ten different approaches at it. That's just the nature of us. As long as it works then it works.

That tap eroder was basically what I was talking about when I was mentioning an edm sinker. Same concept.

RHC - Rockwell Hardness C

HSS Drill Bits - Work well up to the 50ish RHC
Drill - Mild steel, Some tool steel, Some Spring Steel
No Drill - Hard Plate, Anti Drill Plate, 404c Stainless Steel
Pro - Good in Hand Drills and most drilling applications
Con - Has limitations in hardened steels

Cobalt - Works up to 58ish RHC
Drill - Mild Steel, Some Spring Steel, Some Tool Steel
No Drill - Hard Plate, Anti Drill Plate, 440C Stainless Steel
Pro - Good for hand drills and most drilling applications
Con - Has limits with hardened steel

Carbide Tipped - Will drill almost any steel, Hard, Stainless or Mild.
Pro - Drills all steel
Con- Blunt tip requires extreme pressure to produce cuttings. Drill bit is hard to start on all steels.

Diamond Coated Drill Bit - Cuts on most steels(Not Hard Plate) just not for long.
Pro - Will Drill most steels (Not Hard Plate)
Con - Cutting stops quickly after diamond grit has warn off, Then behaves like HSS bit

Solid Carbide Drill Bit - Cuts all steels.
Pro - Sharpened points wont "walk" like carbide tipped bit. Cuts all steel
Con - Sharp tip and fine edges can chip easily and ruin drill bit. Not for hand drills. Expensive!

For more information enter “The Ultimate Guide To Drill Bits” ____ Tube video into your favorite search engine and watch the video.
 
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