Black oxide drill bits and land/margin geometry?

[uart]

This is something I've noticed for a long time and never really understood the reason. I actually had to google what these parts were called (land/margin) to ask my question, so let me ask away.

Almost every time I've looked closely at black oxide HSS drill bits, the part near the leading edge of the flutes looks quite different to that of your typical "bright finished" HSS drill bits. That is, the "margin" area on the leading part of the "land" region always seems particularly raised and prominent (like a ridge) on these black oxide bits.

In contrast to this, on most "bright finished" HSS drill bits I see the margin is less noticeable, with a much more subtly ground relief in the land region behind it.

If anyone's not sure what I'm talking about, this picture of some cheap drill bit from HF should illustrate. If you zoom in close on these bits you can see how pronounced the ridge is on the leading edge of the flute.
See: http://www.harborfreight.com/29-pie...with-3-8-eighth-inch-cutdown-shanks-2642.html

Just curious. Does anyone know why this prominent margin ridge seems so often to be associated with black oxide HSS drill bits in particular?

 

[A_Pmech]

Perhaps you're comparing across drill lines and brands?

The Precision Twist Drill bright and oxide drills I buy (don't remember the list #'s offhand) have the same geometry.

 

[Ign]

That ridge just indicates uber, über cheap Chinese **** I've been weeding these out of my Huot index. I honestly don't know WHY they do that, but it makes for a lightweight bit which just = weak. If you order even the "Interstate" black oxides from Enco they are not constructed this way.

I'm slowly weeding the Interstates (no name import) out too, as I burnt up several in 316SS yesterday. Those that didn't burn up had a ton of runout or one that appeared to spin true drilled a .250 hole from a .221 (#2) bit!! I ordered some Clevelands on Amazon last nite in fact.

 

[Techie1961]

Perhaps you're comparing across drill lines and brands?

Ditto! Most quality drills that I see are pretty consistent in this regard. One thing that I see a lot of in cheap bits is the propensity to have them coated. For some reason, people think that a nitride coating equals quality. It doesn't. You have to have a strong base material first. The coating is just an add-on to suit different requirements.

 

[uart]

Yes this is clearly something to do with the quality and price of the drills. If you have a high quality set of black oxide drill bit then I assume this doesn't apply.

I agree that most of the black oxide bits I see here are on the cheap end of the scale. But the point is this, I've also seen many very cheap and nasty "bright finished" HSS drill bits, and they never seem to have this very prominent ridge like these cheap black oxide one do.

I've seen these in literally dozens of different brands and over a period of many years, and it's *always* the cheap black oxide drill bits that have this particular land/margin geometry.

 

[A_Pmech]

Maybe the cheap black oxide drills all.come from the same company?

 

[larry_g]

Ditto! Most quality drills that I see are pretty consistent in this regard. One thing that I see a lot of in cheap bits is the propensity to have them coated. For some reason, people think that a nitride coating equals quality. It doesn't. You have to have a strong base material first. The coating is just an add-on to suit different requirements.

I've been saying this around here for years. A cheap *** drill bit with gold paint is still a POS. If your not in a production setting the coated drill bits are not going to be for you. If you are in a production setting then you tailor the bit and coating the the material and process being done.

lg
no neat sig line

 

[Ign]

Maybe the cheap black oxide drills all.come from the same company?

This. Most of the cheap 115pc indexes are this way too. In their defense, I did get through two years of school with an inexpensive index like this, but we were mostly just working basic steel and aluminum. Plus it gave us a chance to get good at sharpening by hand LOL

The company that makes these? The Chicom Acme factory in Everywhere, China

Again, I don't know why the brights don't come this way, and I completely respect the OP's curiosity for curiosity's sake, but I just don't care. I've learned to stay away from China bits and that's all I need to know. Most of the places that sell what the OP are asking about are places that are not reputable machine tool suppliers, like HF and Northern.

I also got some YG-1's on ebay which I think were Taiwan, but inexpensive for what it was (parabolic #21) and they walk all over the place in 6061 deep holes. Ironically the best bit for this application was Accupro from MSC, which is just MSC's house brand and I generally don't think much of them.

 

[uart]

Again, I don't know why the brights don't come this way, and I completely respect the OP's curiosity for curiosity's sake

Thanks Ign. Glad to see someone else has noticed this too.

Yeah I don't want to get into a debate about cheap drill bit or anything. I was just cleaning out the shed yesterday and found a few old "half there" sets of cheap black oxide drills. Some were those small 10pc under 5/16" sets that you often see for just a few dollars, others were from cheap driver bit sets where they include a few drill bits in the kit etc. Some were fairly new, others were 10+ years old, all different brands. It just struck me that they all had that really prominent ridge like margin, and none of the other drills in either plain bright finish or the gold coloured coating (even very cheap ones) were like that.

Just to make the point, here's another cheap drill set from HF. Same brand (Drill master) and similarly priced, but this time in the gold TiN finish. You can zoom in on this one and they don't have those super prominent ridges. They just have the more usual land/margin geometry.

http://www.harborfreight.com/29-piece-titanium-nitride-coated-drill-bit-set-5889.html

Anyway I realise that I said this the wrong way around. I didn't mean that all black oxide drills have this super prominent ridge, but rather (at least as far as I can tell) all drills with this super prominent ridge are black oxide.

Just one of life's mysteries I guess.