# Making single flute D bit



## FTlatheworks (Aug 18, 2021)

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?


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## Janderso (Aug 18, 2021)

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


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## FTlatheworks (Aug 18, 2021)

Janderso said:


> 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.


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## FTlatheworks (Aug 18, 2021)

Janderso said:


> 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.


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## Firstram (Aug 18, 2021)

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


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## RJSakowski (Aug 18, 2021)

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.


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## pontiac428 (Aug 18, 2021)

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.


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## ericc (Aug 18, 2021)

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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## benmychree (Aug 18, 2021)

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.


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## FTlatheworks (Aug 18, 2021)

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.


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## benmychree (Aug 18, 2021)

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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## FTlatheworks (Aug 18, 2021)

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.


I wish I knew more about hardening. I don’t have any special equipment. Just a blow torch for my hardening endeavors.


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## FTlatheworks (Aug 18, 2021)

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.


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?


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## Aukai (Aug 18, 2021)

What diameter, center cutting end mill?


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## FTlatheworks (Aug 18, 2021)

Aukai said:


> What diameter, center cutting end mill?


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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## Aukai (Aug 18, 2021)

I use center cutting end mills if I have them for shallow flat bottom holes.


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## FTlatheworks (Aug 18, 2021)

Aukai said:


> I use center cutting end mills if I have them for shallow flat bottom holes.


I initially was going to do that, but I just paid for my fall classes.


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## Firstram (Aug 18, 2021)

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.


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## FTlatheworks (Aug 18, 2021)

I resharpened it, but we will see. I will post a pic soon.


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## pontiac428 (Aug 18, 2021)

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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## Larry$ (Aug 18, 2021)

Even a "center cutting" end mill doesn't plunge cut really freely. There is no relative motion at the center. Difficult for them to clear the chips. Your drill bit grind didn't have any cutting edges near the center! A D bit grind has the advantage of lots of chip clearance. It would be pretty difficult to hand grind a D bit so the split was dead center. 

If your project will permit, drill a small shallow hole in the center, slightly deeper the the final flat.  Then use a drill bit that you have flattened and relieved to form cutting edges.


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## Jimsehr (Aug 18, 2021)

Search on this site for ( Hand grinding a flat bottom drill ) by JimSehr Oct 23 2017.


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## francist (Aug 18, 2021)

Here’s a direct link to Jim’s thread…









						Hand grinding a flat bottom drill.
					

Turning a Harbor Freight drill into a flat bottom drill.  https://photos.app.goo.gl/cFSx3uBtlJKqWXA42




					www.hobby-machinist.com


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## ericc (Aug 18, 2021)

Here are some pictures.  The smaller drill is the one @Jimsehr gave me.  It works great.  The large drill is not center cutting.  You have to have a hole in the center to clear the web.  You can see the primary and secondary faces.


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## FTlatheworks (Aug 18, 2021)

pontiac428 said:


> 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.


That’s what I thought, but I’m no professional. The fact that people used d bits to make the first bored gun barrels I thought was a testament to the D bits reliability. I haven’t had much luck in making this angle right on the old drill bit. Turning drill rod, which I acquired tonight, then grinding two sides at a mild angle/flat seems easier than trying to get this drill bit right.

I’m determined to succeed with both methods.  Being biased towards our own ideas when someone agrees with them is always good too….


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## FTlatheworks (Aug 18, 2021)

ericc said:


> Here are some pictures.  The smaller drill is the one @Jimsehr gave me.  It works great.  The large drill is not center cutting.  You have to have a hole in the center to clear the web.  You can see the primary and secondary faces.


Thank you ericc


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## FTlatheworks (Aug 19, 2021)

francist said:


> Here’s a direct link to Jim’s thread…
> 
> 
> 
> ...


I will read this in a few minutes.


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## FTlatheworks (Aug 19, 2021)

pontiac428 said:


> 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.


Is the borax a must? Also, should I drill with regular bit first?


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## pontiac428 (Aug 19, 2021)

FTlatheworks said:


> Is the borax a must? Also, should I drill with regular bit first?


The borax just keeps the steel from oxidizing and pitting when you do your heat treat.  As far as I know, it plays no other role in metallurgy.  Removing stock with a regular drill and finishing the profile with a D-bit will make it easier when you are going for a flat bottom, but no pilot hole is needed for a  D-bit if you grind a relief on the bottom edge from center on the non-cutting side.  Just extend the 30 degree relief in the diagram below all the way to the center and it will plunge and leave a flat bottom.  For more info, read the attached Deckel manual for a brief, or check some of the texts like Moltrecht if you have a copy, or the Workshop Practice series available on our H-M download library.


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## Jimsehr (Aug 19, 2021)

If you search this site you will find a video where I drilled a steel plate with a flat bottomed drill. I drilled straight into the plate without a starting hole. The drill cut about .005 oversize. I used a new Harbor Freight drill that I cut shorter to make it more stout. Jimsehr


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## FTlatheworks (Aug 19, 2021)

pontiac428 said:


> The borax just keeps the steel from oxidizing and pitting when you do your heat treat.  As far as I know, it plays no other role in metallurgy.  Removing stock with a regular drill and finishing the profile with a D-bit will make it easier when you are going for a flat bottom, but no pilot hole is needed for a  D-bit if you grind a relief on the bottom edge from center on the non-cutting side.  Just extend the 30 degree relief in the diagram below all the way to the center and it will plunge and leave a flat bottom.  For more info, read the attached Deckel manual for a brief, or check some of the texts like Moltrecht if you have a copy, or the Workshop Practice series available on our H-M download library.


Awesome, thank you.


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## FTlatheworks (Aug 19, 2021)

Jimsehr said:


> If you search this site you will find a video where I drilled a steel plate with a flat bottomed drill. I drilled straight into the plate without a starting hole. The drill cut about .005 oversize. I used a new Harbor Freight drill that I cut shorter to make it more stout. Jimsehr


That’s not bad. Unfortunately this hole needs to be perfect, so I will be making a couple thousandths under 5/8 when I make this d bit.


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## Jimsehr (Aug 19, 2021)

FTlatheworks said:


> That’s not bad. Unfortunately this hole needs to be perfect, so I will be making a couple thousandths under 5/8 when I make this d bit.


I wish you well with your d bit. I can make a flat bottomed drill in about 10 to 15 minutes. So I could make an undersized flat 5/8 and follow it up with a flat 5/8 if I had to be sure of finished size. 
Jimsehr


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## FTlatheworks (Aug 19, 2021)

Jimsehr said:


> I wish you well with your d bit. I can make a flat bottomed drill in about 10 to 15 minutes. So I could make an undersized flat 5/8 and follow it up with a flat 5/8 if I had to be sure of finished size.
> Jimsehr


How did you grind that so nicely. I’m at the mercy of my crappy grinder mounted in a dumb place at work. I want to design a surface grinder with an XYZ vice using a cheap bench grinder, or any motor for that matter. I have tried to match your clearance angle and it still doesnt cut worth a damn. Is it possible I have burnt the bit up grinding on it. Maybe I took some hardness out? You guys are making it seem so easy, but I have never seen anyone do it nicely in person and have it come out like a pricey flat bottom bit, D bit, or End mill holes. I should also mention I am drilling this hole 1/2 inch depth at a 10 degree angle.


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## Janderso (Aug 19, 2021)

Jimsehr said:


> If you search this site you will find a video where I drilled a steel plate with a flat bottomed drill. I drilled straight into the plate without a starting hole. The drill cut about .005 oversize. I used a new Harbor Freight drill that I cut shorter to make it more stout. Jimsehr


Yeah, I found that Jim.
Pretty sweet. It looks like a center cutting end mill made from a broken drill bit. 
A keen eye for sure.


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## FTlatheworks (Aug 19, 2021)

FTlatheworks said:


> How did you grind that so nicely. I’m at the mercy of my crappy grinder mounted in a dumb place at work. I want to design a surface grinder with an XYZ vice using a cheap bench grinder, or any motor for that matter. I have tried to match your clearance angle and it still doesnt cut worth a damn. Is it possible I have burnt the bit up grinding on it. Maybe I took some hardness out? You guys are making it seem so easy, but I have never seen anyone do it nicely in person and have it come out like a pricey flat bottom bit, D bit, or End mill holes. I should also mention I am drilling this hole 1/2 inch depth at a 10 degree angle.


Alright, I get it now. The angles on a drill bit are much more complex and the pics don’t capture what really needs to happen. I think I understand d bits and making a flat bottom from old bits. Here it is guys! Thanks for sticking with me to figure this out . I will show the bit, then the results in a little bit… no pun!


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## FTlatheworks (Aug 19, 2021)

Did better, not great. I think I could get the bit better with more work.


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## Jimsehr (Aug 20, 2021)

FTlatheworks said:


> Did better, not great. I think I could get the bit better with more work.


If you mail me a drill I will sharpen it for you. And that way you will have a model. So that you can learn to sharpen your own. You pay postage both ways and it’s a deal. Jimatcf@hotmail.com
How you learn practice, practice, practice.
By the way ANY drill will probably cut 3 or 4 thousands oversized.
Most important thing grinding a flat bottom drill is splitting the point.
Jimsehr


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## FTlatheworks (Aug 20, 2021)

Jimsehr said:


> If you mail me a drill I will sharpen it for you. And that way you will have a model. So that you can learn to sharpen your own. You pay postage both ways and it’s a deal. Jimatcf@hotmail.com
> How you learn practice, practice, practice.
> By the way ANY drill will probably cut 3 or 4 thousands oversized.
> Most important thing grinding a flat bottom drill is splitting the point.
> Jimsehr


I’ll take a pic, but I got it down last night. I appreciate the offer though.


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