Black Oxide Drill Bits?

[Jim Koepke]

Anyone know what this means?

The Orange Borg had a lot of stuff in the aisles for Christmas season. One of them was a 35 piece set of fractional 'Black Oxide Drill Bits" labeled Ryobi for $3.

They are in a plastic index. Not the greatest, but it will keep them from getting lost in the bottom of a drawer.

Figured they would be good for wood. There are multiple bits of the smaller sizes.

Quan size
7 ----- 1/16
7 ----- 5/64
6 ----- 3/32
3 ----- 7/64
3 ----- 1/8
1 ----- 9/64
2 ----- 5/32
1 each of sizes 11/64 through 5/16, there isn't a 9/64 bit

At that price it may be a good set for when someone wants to borrow a bit.

jtk

[Bill Houghton]

Black Oxide is a coating on the bits. It's intended to reduce corrosion, see here: https://en.wikipedia.org/wiki/Black_oxide . It's very common on jobber's (standard length) drill bits. Of itself, it doesn't indicate quality or lack thereof: my uncle's industrial-grade drill bet set is black oxide-coated, and so is the cheap Chinese set that I keep for times that I have to drill something really gross/might ruin a good bit.

Almost certainly Chinese-made, and how good they are then depends on Ryobi's quality control expectations and follow through.

[Jim Koepke]

Black Oxide is a coating on the bits. It's intended to reduce corrosion, see here: https://en.wikipedia.org/wiki/Black_oxide . It's very common on jobber's (standard length) drill bits. Of itself, it doesn't indicate quality or lack thereof: my uncle's industrial-grade drill bet set is black oxide-coated, and so is the cheap Chinese set that I keep for times that I have to drill something really gross/might ruin a good bit.

Almost certainly Chinese-made, and how good they are then depends on Ryobi's quality control expectations and follow through.

Thanks for the info Bill. The set is made in China. My main set of drills are a numbered set in two indexes so I thought a cheap fractional set wouldn't be a bad idea.

One of the 1/16" bits was tried in a piece of wood and went through without trouble in an egg beater drill, so far so good.

jtk

[Bill Jobe]

I was I'm charge of hardware for the last 2 years before I retired and learned that the black oxide, at least at that time, was phosphorus, and a bit oily.
Don't know if we are talking about the same thing, though.

An amusing thing happened while I was still running CNCs. We frequently used a triagular insert that came in metalic, black and yellow. We had one operator who was very cocky and arrogant. He told everyone that the yellow inserts were by far superior, that they lasted well beyond the lifespan if the 2 other colors.
One day the representative of the manufacturer of the inserts we used came in and we talked with him for several minutes as a group. At some point the operator I mentioned commented on the superiority of the yellow tips (actually gold in color). The rep from the tool company told him the gold color was simply a coating that had no effect on the quality of the tip.
Personally, I had to fight hard not to laugh. Not sure how the others handled it.

[Patrick Chase]

Anyone know what this means?

Black oxide is magnetite (Fe3O4), an oxide of iron that is *not* rust (Fe2O3) and that is hard and mildly rust resistant. It also provides some lubricity when machining ferrous metals.

A "black oxide" drill bit is one that has gone through a conversion process that creates a layer of magnetite on the surface. It's very similar to what the gun folks call "bluing". It isn't a "true" passivating layer like patina on bronze, because it will still eventually turn into rust.

There are excellent black-oxide drill bits on the market, for example I have US-made Chicago-Latrobe 150 and 190F black-oxide HSS bits and find those to be quite good. One "gotcha" to be aware of is that black oxide bits have been known to be "faked" by painting low-grade steel or even iron black.

[Chris Fournier]

What others have said about black oxide. When I buy drill bits I buy made in the USA and get what I paid for every time.

[Patrick Chase]

One additional remark: In my experience black oxide doesn't buy you much of anything for wood or plastics. The hardness difference between a black oxide HSS bit and an uncoated one is negligible (and becomes zero once you sharpen :-) and the lubricity advantage is only applicable when drilling ferrous metals.

I use uncoated HSS bits like these for wood and plastic. They're not cheap, but quality tools seldom are. This is the corresponding black-oxide set. I suspect that the price difference is because the blackening process doesn't add significantly to the cost (it's quite simple) and black oxide bits are more popular and therefore higher volume.