Drill bits which ones and why
 

Over the years I've learned to slow-down the speed when drilling metal, and use a good cutting oil, but the bits still break, get dull, lost, etc. So I'm sort of always on the look-out for a new set. Anyone know the difference between Black Oxide, Titanium, Cobalt, etc.?? What do you buy, and why?

I bought a drill Dr. once. I had it out of the box for about 30 minutes before I wanted to throw it out the window. Probably just don't know how to use it, but I could never get small diameter bits sharp(er). Anyone have experience with bit sharpeners and could comment on which ones work, if any??

I'd post a picture of my drill bit drawer, but it probably looks like everyone else's. Lots of sets, mostly incomplete. I know there's probably a few out there that have very complete, and sharp sets. :eek::eek:
Just curious, and we're talking "metal". What do you buy? Do you run'm until they're broken, lost, or dull. Or, do you sharpen them, and if so, how?

I've got a Drill Dr.

I haven't used it in a couple of years. When I sharpened all the bits I had it seems like I now have a lifetime supply.

Good quality high speed steel bits do the trick for most applications. (not China made)

Cobalt or Carbide tiped drill bits are used to drill through hardened material but are expensive for everyday use, and can chip easily when used improperly, due to their hardness.

You also must develope a feel for machining. To much speed burns up the bits.
Cutting oil, while it lubes and aids in cutting, it also generates more heat. Heat kills the cutting edge of the drill.

Unless you can flood the part with cutting oil or water soluable cooling medium while drilling, you will only generate more heat by adding oil, wd40....

Moderate speed with enough pressure to cut, and cleaning the flutes regularly, really helps the life of a bit, but all will eventually need to be sharpened.

If you manage to generate enough heat to wear the sides of the drill bit along with burning up the lead cutting edge , you might as well throw it out, and buy a new one.

As an ex-machinist I have learned how to sharpen a drill bit on a bench or pedestal grinder.

I just get a big set of titanium nitride coated drill bits from Harbor Freight... that way I am not too attached to them... I do the slower speed and oil as well.

+1

I Have a higher end Drill DR and love it.

I know many alarm/radio/accessory installers love using a stepped Unibit. I haven't myself but have watched and it seems to be quite convenient and effective.

Black and Decker bullet bits are nice because they start themselves.

Standard Hitachi bits from Lowes are incredibly nice in their index and are not made in China.

Any european bit is going to be amazing but will cost a pretty penny in the weak economy/high euro zone we are in.

the bottom end of the scale for drill is high speed steel black oxide drill.. They are for general use and dull easliy in non oiled situations.

Cobalt drills are a type of High speed steel drill . The metal has a higher percentage of Cobalt in it to make the drill more heat resistant and tougher. Usually these drills have a nicer self centering drill point and work well for most aplications. They dont chip like carbide drills do


Carbide drills are for worked hardened material and for high speed use.. they are brittle and break easy.but are very hard. I would avaoid using them to hand drill holes .

Titanium coated drills usually start out as just Highspeed drills or cobalt drills with a extra but of harden coating on them .. Slightly better than non coated drills

if you are drilling repeated holes of the same size ie. mfg a part, i would suggest a coolant fed indexable insert drill. best of all worlds.

coolant flushes chips out... numero uno rule of drilling expel chips. oil water air.

helical inserts are indexable (twice) and helix allows chips to curve more and expel themselves.

sandvik(alma mater) komet, mitsuibishi, iscar(alma mater).

if drilling just oddball holes buy a HUOT drill index. pick flavors metric standard ,american made no broken bits quality u.s.a mfg. plus they ARE SIZED CORRECTLY!

+1 on what Charles says about USA Drills

As others pointed out the quality of the metal that the bit is made from will make a huge difference in how long it lasts. Don't waste money on micro grain carbide and similar unless you are drilling hardened metal in a drill press because it is to brittle and the bit will chip or shatter and they are pricey. Another thing to consider when you are buying drill bits is that you can get split points as well as standard points. I prefer split points because I feel like they walk less (the web is thinner because of the split) even though the end is 135 degrees instead of 118 degrees. I am hard on drill bits and I treat them like they are made to be thrown away so I use cheap bits (harbor freight) for most jobs and good quality bits when I am working on something important like drilling and tapping a hole in an engine block etc. I have a Drill Dr. but I have always found it easier and quicker to sharpen bits on a pedestal grinder.

+1

The overall angle of ~120 deg on a drill bit is not as important as the cutting-edge angle.
A skilled Machinist can grind a drill bit on a bench-grinder just by hand; anything over 1/4" diameter is easy but, when it comes to smaller bits, you'll need a strong light and magnifying glasses on your nose so you can see what you're doing.
Go to a Machine shop and offer a case of beer to a Machinist to show you how to hold the drill and get the right angles when sharpening on a bench grinder. (Safety glasses!)
Practise with a 1/2" drill on your own bench grinder; a clean wheel is a must.
I sharpen my bits by hand; with a strong light and magnifying glasses.
When drilling, the way that the chip comes out tells me a lot about whether the angles are good, or the speed is right, or how much force to apply.
And I use cutting oil as lube and to reduce heat. (Right on, Sherwood)
Practise will get you there. :)
I believe a Drill Doctor works if you follow the instructions.

"Cutting oil, while it lubes and aids in cutting, it also generates more heat. Heat kills the cutting edge of the drill...."

Hmmm. How can drill lube add more heat than that generated by the cutting tool? MHO: The purpose of a cutting oil is to reduce friction, transfer heat and thus provide a better cut.

Sherwood

my understanding is that most drill bits have an angle that is 'general' purpose - not optimal for wood cutting & not optimal for metals either. Different metals require or benefit from different angles - a student machinists text or a handbook will list what angle for what metal.

For DIY work, I bought a big Sears set of HSS bits in the 1970s. I then replaced the worn "standard" sizes with Ti coated bits & that has worked for me.

Unibits are fine for thin sheet metal. I would avoid them for something thick.

Kerosene is a sort of general lube. People have used soap way back when...

Same here and they actually work quite well even on harder steel! Price is right too.

My father was an engineer and knowledgable regarding machine techniques. He could easily sharpen a bit with a bench grinder. I could never get the hang of it and bought a Drill Doctor. I was less than happy with the DD the first time I used it. But, a quick call to DD customer service informed me of what I as doing wrong. Now works like a charm.

Steve

Sherwood,
Take any statement out of context and you will be perplexed. Consult a machinist on the posting in its entirety...Then you will know why.
Ponder this for a moment...When drilling a blind hole, where would all that "hot" oil go? Thats right! It will puddle right there in the drill hole and heat the drill bit quicker than without.
When drilling without oil, at the proper speed and feed, the bulk of the heat stays with the chip, while the denser parent material will stay cooler. Add oil, and more heat is transfered into the drill bit, which is the lesser mass.
The previous post on drill bit angles for different materials is completely correct.

My father was also an engineer, deeply involved with manufacturing and finishing hydraulic castings. His advice to me for drilling was not to slow down, as it is the heat that destroys drill bits. They would set their machines to apply so much pressure that the the bit would start to bend, then back off one notch.

Thank you for all the replies. I was probably a bit too impatient with the DD, and should give it another try. New bits are always a pleasure to use, but I can hear my Dad in the background "you're wasting money, just sharpen the damn things."

Irwin makes the Turbo-Max bit which is one of my best sellers. It is a pilot point and resists walking. They are warranteed not to fail but only in 1/4" and larger sizes. I've had a set for quite some time and only had to replace a few of them.