Making single flute D bit

[FTlatheworks]

Could I use 4140 tool steel to grind and harden a single flute D bits for drilling flat bottom holes in mild steel? I would make it on the lathe, harden with a torch, then use it in a drill press. Do I need to use drill stock instead?

 

[Janderso]

Drill rod is what I use but you could always get creative.
Check Hudson’s tool for 4140ht (as one source) to see how hard it can get compared to drill rod.
I’d be curious

 

[FTlatheworks]

Drill rod is what I use but you could always get creative.
Check Hudson’s tool for 4140ht (as one source) to see how hard it can get compared to drill rod.
I’d be curious

I don’t want to use 4140, it’s just what I have.

 

[FTlatheworks]

Drill rod is what I use but you could always get creative.
Check Hudson’s tool for 4140ht (as one source) to see how hard it can get compared to drill rod.
I’d be curious

It says 4140 is LSS, I’m assuming low speed steel. It’s used for gears, wrenches, flanges, and all other kinds of tools, but not cutting tools.

 

[Firstram]

Grab a regular bit and flatten the end. Drill hole then flatten the bottom with modded bit.

 

[RJSakowski]

Fot a flat bottomed hole, I ground the end of a deill flat and ground relief. As @Firstram said, drill to depth with a regular drill first and finish with the modified bit.

 

[pontiac428]

As far as hardness, 4140-HT < M2 < O1-HT. Depends on the diameter and depth of the hole and what base material you're cutting, but D-bits are very capable for flat bottomed holes. They're a little slow and don't clear chips well, but if you give them good relief on both sharp edges they get the job done.

 

[ericc]

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.

 

[benmychree]

4140 is not a tool steel and will not generate sufficient hardness for cutting tools. As others have noted, grind a regular twist drill to a flat bottom configuration, adding clearance to the cutting edge and secondary clearance behind that clearance for chip space, and use it to clean out the bottom of the previously drilled hole; this is standard procedure in industry. It is best to enter the flat bottom drill into the hole before rotating it.

 

[FTlatheworks]

Here the one I tried to make for a drill bit. The second is the hole it made before it stopped working. Tried to adjust angle many times before I gave up on the middle of it.