Making single flute D bit

It may not have had enough clearance, also should have a second clearance angle, and the margin could be split or thinned, in other words, it should look more like an end mill point.
 
ericc said:
You can make a flat bottom drill from an old drill bit. 4140 is not an appropriate steel for making cutting tools. It is more suitable for mandrels, blocks, screwdrivers, wrenches, pry bars, etc. If you have some Kasenit or old fashioned pack hardening equipment, you could try to case harden the 4140. In a pinch, you can use iron wire and boric acid with a torch and get it screaming hard (that's as hard as it will go without grain growth or decarb) with no drawing temper. It will cut...for a while.
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I wish I knew more about hardening. I don’t have any special equipment. Just a blow torch for my hardening endeavors.
 
benmychree said:
It may not have had enough clearance, also should have a second clearance angle, and the margin could be split or thinned, in other words, it should look more like an end mill point.
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Ok, I’ll give it another go. I figured the drill rod D bit would work better and make a nicer hole, but I guess it’s my grinding skills. Anyone have a modded drill bit handy to snap a pic of?
 
What diameter, center cutting end mill?
 
Aukai said:
What diameter, center cutting end mill?
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No a drill bit ground to drill flat bottom holes. 5/8 is the diameter. Are you saying I should use an end mill? I have drill stock I can get for super cheap. I can’t afford to buy anything right now. The drill stock, or old drill bit I have laying around. I can get those for a dollar, or two.
 
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I use center cutting end mills if I have them for shallow flat bottom holes.
 
Practice sharpening the bottom of that drill bit, it's free. As mentioned above, make it look like a the bottom of an end mill.
 
The flute profile of a drill bit is dependent on the point angle. I'm not surprised it didn't work without re-grinding the base and flank to something that provides better angles for cutting. You won't get any center cutting with a cut-off drill, either. My effort would be spent on making a D-bit for bottoming, like the plan you started out with. If you don't have any HSS stubs handy, get a stick of some O1 or W1, and slather it with damp borax before heating and quenching the roughed tool like @ericc said. Then clean it up on the wire wheel and do the final grind. It will work. D-bits are seriously underrated in this world of easy-bake insert carbide. They got machinists through a lot of challenges for a century and a half before computer generated tooling came along. There are some great chapters in the texts about D-bits, they shouldn't be so easily disregarded.
 
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