Drill bit hardness

[MikeF2316]

I needed to turn one of my Gearwrench Impact Hex bits into a security version. So I chucked it up in the lathe and took out a suitable center drill and proceeded to make a suitable centering hole. All no problem. Then I took one of my tungsten coated twist to finish the hole. Well, I might as well have been using a piece of coat hanger! I tried a slightly smaller one that was brand new, and it also made no progress - not even small chips, nothing but heat. I was able to find a larger center drill in my stash that had a long and large enough guide area to finish the hole. This center drill, like the first one had no problem drilling the material, even generating some continuous spiral waste.

So what are these center drills made from? Gearwrench says their hex bits are made from "Impact Grade Alloy Steel". I'd like to have at least a basic set of twist drill bits hard enough to do this if and when there is a next time.

 

[Jason280]

I'd be curious if you might have work hardened the piece without realizing it. I recently had to drill a hole sideways through a 1" chrome Craftsman deep well socket, so I drilled a 1/8 or 3/16" pilot hole....went through like butter. Stepped up to my needed hole diameter, which was around 5/16, and burned out two different bits. Ended up having to finish the hole with a carbide bit...

 

[CallumRD1]

What size drill were you using and what speed were you running it at?

 

[larry_g]

Coated drills mean nothing. A manufacture can put some fancy named coating on a twisted coat hanger. Most of the coatings that are sold in the retail store are worth nothing to the average homeowner. Coatings on good drill bits are designed for production use in specific materials. Spend your money on good quality bits and you will succeed. Most common center drills are just high speed steel. There seems to be a thread on drill bits here every month, Search out a few and you will find that a few name brands come up in every one.



lg
no neat sig line

 

[BillK]

Solid carbide is what you need. They cut that type of stuff like butter but require a very rigid setup. In the lathe like you had it would be perfect.

 

[MikeF2316]

Coated drills mean nothing. A manufacture can put some fancy named coating on a twisted coat hanger. Most of the coatings that are sold in the retail store are worth nothing to the average homeowner. Coatings on good drill bits are designed for production use in specific materials. Spend your money on good quality bits and you will succeed. Most common center drills are just high speed steel. There seems to be a thread on drill bits here every month, Search out a few and you will find that a few name brands come up in every one.



lg
no neat sig line

One thing I didn't mention, I was using cutting oil as well. I used a 3/32 and 7/64 bits with no effect. I was using 600 rpm, (feeding by hand) which seemed like a slow enough speed as I wasn't in a rush and only had one hole to drill. I used the same speed for the center drills. The large one that I finished up with had a minor diameter of 3/16" and length of 1/2".

I was also under the impression that center bits weren't anything special, so was surprised at how they had no problem when the other bits wouldn't even make a chip.

My research seems to indicate I need a set of Cobalt bits for drilling the harder steels, but I wanted to hear it directly. Threads here seem to have questions and answers about general quality, not a specific answer to a question about a specific type of steel.

Thanks for any additional help.

 

[MikeF2316]

Solid carbide is what you need. They cut that type of stuff like butter but require a very rigid setup. In the lathe like you had it would be perfect.

Thanks for this. I was leaning to cobalt.

 

[larry_g]

One thing I didn't mention,

I was also under the impression that center bits weren't anything special, so was surprised at how they had no problem when the other bits wouldn't even make a chip.


Thanks for any additional help.

A second thing you failed to mention is brand and materials of your bits that failed. I'm assuming they are discount bits from the hardware store?

Triumph or Cleveland twist are good brands, or used to be, I haven't bought many bits lately. Cobalt is a harder bit for harder materials. Carbide is harder yet but more brittle. And again a carbide bit from ebay for a dollar is probably not of the best quality.

lg
no neat sig line

 

[MikeF2316]

A second thing you failed to mention is brand and materials of your bits that failed. I'm assuming they are discount bits from the hardware store?

Triumph or Cleveland twist are good brands, or used to be, I haven't bought many bits lately. Cobalt is a harder bit for harder materials. Carbide is harder yet but more brittle. And again a carbide bit from ebay for a dollar is probably not of the best quality.

lg
no neat sig line

The drill bits were from a set that I've had for at least 10 years, this is the first real problem I've had with them. I've drilled large holes in stainless and mild steels with them. I don't know where they came from, (but I'd guess not a country known for high quality tools) they were a gift from my father. I recognize they're the problem, I want to get some better ones, ones I keep aside and only use when there's a issue with this set.

 

[454ragtop]

I'd recommend Triumph cobalt. That's what comes in the Ridgid/Snap On screw extractor kits, work good drilling hard bolts. Carbide are very brittle, tough to use the smaller sizes without breakage.

 

[Indexmill]

It seems odd that the center drill cut fine even the second time after failing with drill bits. As said above, center drills are just HSS but a good brand of center drill will be the finest HSS.

You never did say what brand the drill bits were. Do you KNOW that they are HSS?

I am kinda surprised that the center drill cut it fine.

 

[Astro_Pneumatic_Tools]

How hard are drill bits? Most we have tested are 61-66Rc for M2 HSS which yours would be just playing the odds
What is the "impact grade alloy steel" likely 6150 CR-V if they dont have Cro-Mo stamped into them.
What is their hardness? Likely 44-50Rc
Why do center drills drill into (most) things easily? Cutting angle, chisel edge size and shank mass and size compared to a twist drill. You have a very sturdy tool and little to no heat when you're dealing with a mostly solid, short, minimally fluted center drill.

What you likely need is a small end mill to follow a center drill or if you must use a twist drill, M42 Cobalt HSS and change your feeds/speeds based on the drill diameter.

Drilling into hardened/quenched alloys is tough, it's not just a matter of having a drill bit that's harder than the material. Some materials just don't like to move, like 303 vs 304 stainless - -similar hardness but one is a pain to machine.

 

[larry_g]

Another note, I use screw machine length bits for the goto bits. I use the longer bits if I have to. They are a lot stiffer and less tendency to move around or wind up.

lg
no neat sig line

 

[neophyte]

Drill bits designed for drilling armor plate usually have a straight or almost straight flute.
Some centering drill bits have a similar or closely similar flute design.
It’s possible this flute design works better on the hardened steel of the screwdriver bit.

Centering drills are also somewhat specialized.
A hundred or possibly a thousand times more spiral twist drills are manufactured than centering drills are manufactured, and that is per size.
Since most drill bits are manufactured on industrial production lines in huge quantities, it’s possible that the centering drills, routinely come of production lines meant for industrial use, whereas common twist drills are more likely to come off of production lines meant to supply cheaper home lines.

As far as coatings go, titanium nitrate provides an anti galling characteristic for certain metals like aluminum, and even cheap twist drills may benefit from a cheap titanium nitrate coating if you’re extensively drilling aluminum.
I don’t know that the coatings will do much for harder steel, unless the bits are industrially coated bits that can cost two or three times what uncoated industrial bits cost.

Drilling plunge speed can also come into play, because some metals beed to be drilled very quickly to prevent work hardening.
With covalt bits you’re actually supposed to use high rpm drilling speeds rather than lower speeds.

 

[Maui]

Your drill bits are probably made from a lower alloy content tool steel rather than an M grade high speed steel. They will likely be softer than an equivalent M2 or M42 drill bit, and not do the required job as easily or as effectively.

 

[MikeF2316]

To address questions:

The drill bit set I've been using is one of those complete set, triple index kits that includes 1/16-1/2, 1-60 and A-Z. Plus it came with some extras in fractional sizes 1/8-3/8 which is why I have some brand new ones. I can't imagine my dad buying me anything but HSS. As I said above I have drilled stainless (don't know the grade) successfully with them.

I was also very surprised the center drill worked, I didn't expect it to. But I gave it a shot since the original smaller one had no trouble.

Since I've drank lots of the Milwaukee Kool-Aid, I stopped at Home Depot on my way home from work and picked up this cobalt set as it was the path of least resistance. No idea as to the grade, I wasn't able to find out with a quick googling.

https://www.homedepot.ca/product/milwaukee-tool-cobalt-drill-bit-set-15-piece-/1001041176

I put the 3/16 in the lathe, it went through the hex bit like it was butter.

I had a sale flyer from KBC tools in my mailbox. And what do you know, they had solid carbide bits on sale! So I ordered a 3/16, 1/4 and 5/16. If I need anything bigger in the future, I'll order as needed.

 

[Astro_Pneumatic_Tools]

No idea as to the grade, I wasn't able to find out with a quick googling

https://www.homedepot.ca/product/milwaukee-tool-cobalt-drill-bit-set-15-piece-/1001041176

M35, which is great too.

 

[Dingleburry]

Last time i needed to drill a hardened steel, i heated it up.
The bits i use are pretty good. Lawson products in house brand. Just HSS.
It was a hardened pin, with a ****** plastic handle on the end that broke. Tried drilling didnt touch it, sharpened my bit just in case, tried it again,just mangles the cutting edge. ****. What do now?
Broke out the propane torch, fed her some heat, didnt check temp. I should have though. It was far from glowing hot.
Needless to say, it drilled. Swarf came out straight (not curly) with torn/jagged edges.

 

[Dingleburry]

M35, which is great too.

Curious on your bit testing. Can you elaborate more on it?
Did you test at multiple points? As in are the full length of the flutes hardened? What was shank hardness? And hardness between cobalt and HSS, brands? Any major outliers Or are they all pretty close regardless of price/brand?
Also did you test them for durability in drill press/cordless drill? Notice if the hardest ones are too brittle?
Etc?

Thanks

 

[MikeF2316]

M35, which is great too.

Thanks for that.

The Gearwrench bit was not marked with "CR-MO" like all my other impact stuff (including my Astro Pneumatic stubbies) so I guess it's 6150 CR-V. So is that harder than CR-MO? I was honestly surprised I had trouble drilling impact grade, I thought they were soft enough to drill easily to prevent shattering.

 

[Astro_Pneumatic_Tools]

Curious on your bit testing. Can you elaborate more on it?

Not in too much detail, but we do drill bit testing here and independently including spectrometer tests year-round. Many dozens of tests a year.

Did you test at multiple points? As in are the full length of the flutes hardened? What was shank hardness?

Yes when possible, drill bit size permitting. Whether by differential heat treatment, draw back annealing or via machining process cooling, the shank is more often than not softer than the chisel point and flutes. Usually around 2-8 sometimes 10 points, which is to say its still very hard.

And hardness between cobalt and HSS, brands? Any major outliers Or are they all pretty close regardless of price/brand?

Cobalt is a HSS, but yes between cobalt added 5%, 8% and no cobalt added there often is hardness difference, but not as much as you would expect. Usually 3-6 points above M2 depending on the intended use and design of the drill bit. I have not seen major outliers across brands or COO's among same alloys. M2 will usually be within 2-5 points of another among same use drill bits. Differences are more pronounced among different or specialty tool steels.

Also did you test them for durability in drill press/cordless drill? Notice if the hardest ones are too brittle?

Drill press
Cordless drills
Air drills
Impact drivers
Left-hand drill bits in cordless tools

Harder drill bits will always break easier, but also hold an edge longer. But usually not in controlled testing, you need to use the bit like a mechanic does to see this difference in breakage. Cobalt bits aren't easier to break when abused just from the few points in hardness alone, adding that cobalt % displaces other minerals found in M2, M7 or otherwise that help make the bit ductile. But cobalt's high red-hot hardness means it's hardness doesn't just disappear when really going to town so it has its benefits.

Thanks for that.

The Gearwrench bit was not marked with "CR-MO" like all my other impact stuff (including my Astro Pneumatic stubbies) so I guess it's 6150 CR-V. So is that harder than CR-MO? I was honestly surprised I had trouble drilling impact grade, I thought they were soft enough to drill easily to prevent shattering.

Depends on the application, but yes Cr-V is usually a few points harder, and more difficult to drill and machine once hardened/quenched.

 

[HAP]

You SFPM was much different with the smaller bit. 600 RPM was likely way too fast. 300 is probably the highest it should have been with the larger bit...

 

[fsae0607]

Ummm....

https://www.harborfreight.com/33-pc-security-bit-set-68459.html

https://www.amazon.com/dp/B000O5XDOG/?tag=atomicindus08-20

 

[MikeF2316]

Ummm....

https://www.harborfreight.com/33-pc-security-bit-set-68459.html

https://www.amazon.com/dp/B000O5XDOG/?tag=atomicindus08-20

That's cool, except... And I see I never mentioned the size, but I was doing this to a 13 mm hex bit - it's hard enough to find a hex bit in that size. I wasn't able to find a security bit.

 

[fsae0607]

That's cool, except... And I see I never mentioned the size, but I was doing this to a 13 mm hex bit - it's hard enough to find a hex bit in that size. I wasn't able to find a security bit.

Ah ok. I was thinking: the effort to purchase a cobalt/carbide drill bit on ebay, you could just buy a security bit set.

 

[purplezr2]

That's cool, except... And I see I never mentioned the size, but I was doing this to a 13 mm hex bit - it's hard enough to find a hex bit in that size. I wasn't able to find a security bit.

Curious to what it is for?

 

[MikeF2316]

Curious to what it is for?

It's not actually a security bit in the true sense. The crank on my patio umbrella is a 1/2" hex crank, held on with a 10-32 screw down the center. The "allen head" it goes into is plastic and stretched out so the crank only spins, doesn't deploy the umbrella. My 13mm hex bit fit into that plastic nice and tight, but the bolt was in the way. Now I can deploy my umbrella with a ratchet! And since pictures are worth 1000 words:

Crank and empty socket:

Drilled Hex key installed:

And the hex key won't live in there, I'll have to go to my toolbox to open the umbrella every time I want to.

 

[Dingleburry]

Not in too much detail, but we do drill bit testing here and independently including spectrometer tests year-round. Many dozens of tests a year.

That is great info thanks!

I have a set of lawson products bits that i love. The falcon line.
I was curious about their "limits" so to say.
So i piloted about 40 1/8th holes in 1/4 steel plate, then WITHOUT oil used a 5/16 bit, max drill speed and feed pressure. Was an m18 fuel drill whatever the rpm is. The bit cut to the end no problem, but the drill was so hot you couldnt touch it.
I dont use cutting oil anymore ever, unless its a gr8 bolt or 1inch+ deep hole.

Then i used lawson "premium" regency bits and i chipped the tip first use enlarging the hole, sharpened it, chipped it again. Never used their "premium" again. And when the cheap ones didnt cut something, their premium didnt either. Garbage!

Thats why i was asking if you did real world tests and if you have found the bits on the harder end of the range too brittle. Also been using/abusing the same set for 5+ years, with resharpening of corse. Just wondering if ill run into a softer part eventually lol
99% of my drilling is cordless drills.

Even found pic, have one of tip but too large wont upload

 

[Szilagyi]

I find brand and country of origin (ie how they're made) make the difference, not claims of steel and coating. I am poor and use regular store brand drills for most things, but I have a 13 piece set of Chicago Latrobe drills for hard stuff. They are black oxide coated hss with standard chisel tips and they outdrill any of the fancy drills I own. They are pricey though. Another good but pricey brand is Norseman.

 

[MikeF2316]

I visited KBC tools and grabbed 3 solid carbide bits. Made in USA! 1/8, 1/4 & 5/16. I should be ready next time.

 

[BFHtime]

I visited KBC tools and grabbed 3 solid carbide bits. Made in USA! 1/8, 1/4 & 5/16. I should be ready next time.

please post a link

 

[ClappedOutBport]

To address questions:

The drill bit set I've been using is one of those complete set, triple index kits that includes 1/16-1/2, 1-60 and A-Z. Plus it came with some extras in fractional sizes 1/8-3/8 which is why I have some brand new ones. I can't imagine my dad buying me anything but HSS. As I said above I have drilled stainless (don't know the grade) successfully with them.

I was also very surprised the center drill worked, I didn't expect it to. But I gave it a shot since the original smaller one had no trouble.

Since I've drank lots of the Milwaukee Kool-Aid, I stopped at Home Depot on my way home from work and picked up this cobalt set as it was the path of least resistance. No idea as to the grade, I wasn't able to find out with a quick googling.

https://www.homedepot.ca/product/milwaukee-tool-cobalt-drill-bit-set-15-piece-/1001041176

I put the 3/16 in the lathe, it went through the hex bit like it was butter.

I had a sale flyer from KBC tools in my mailbox. And what do you know, they had solid carbide bits on sale! So I ordered a 3/16, 1/4 and 5/16. If I need anything bigger in the future, I'll order as needed.

Are they in a black, metal case, single latch on the front? Fractional left, number top, letter, right? I once dulled a harbor freight drill drilling 3" of aluminum in the lathe with one. No it wasn't me. I've drilled well deeper in tough steel with a quality bit and have it still be perfectly sharp. Also, oil can keep drills from biting sometimes and cause work-hardening. It doesn't always help.

Spark test yours.
Dull Orange sparks, few in quality, long travel distance, grinds slow: Best, what you will find on almost all MT drills
Yellow, slow: Can be ok, but don't expect wonders
Short, bright, whitish, explode like fireworks: Seems to be junk
All else: Also junk.

I've hand ground some drills that when away so fast you'd think you were grinding lead. Best just to toss them in the scrap bin and grab another.

I visited KBC tools and grabbed 3 solid carbide bits. Made in USA! 1/8, 1/4 & 5/16. I should be ready next time.

Be careful. Easy to break. No sudden movements.

 

[MikeF2316]

please post a link

https://www.kbctools.ca/products/search/?Keyword=hi-tuff carbide

 

[ChevyEFI]

I would have spent a lot of time finding a hex standoff. More than you did drilling your socket. Good work / discussion.