Drill bit questions

[MightyThor]

I know this is probably the wrong place for this post, but all you here seem to be machinists of one sort or another so I need info and advice. I have bought my last set of cheap sh@# drill bits. The last set I got was so bad that Harbor Freight turned them down. I have literally unscrewed half of the bits when the cutting edge catches and the flukes untwist. So I am gonna buy good bits. So what is the best. I can find High speed steel, cobalt, split tip, multi tip, carbide tip, I expect to be drilling steel, including some harder stuff like circular saw blades etc. Will also be drilling aluminum , plastic, brass, wood, etc. Also, what is the difference between sets that are fractional, and those sets with numbered drills.

[mtgrs737]

An industrial supply is a good place to look for drills, but expect to pay a good price for them. The cobalt steel drills are supposed to be better that High Speed Steel but a good HSS bit will last a long time if not overheated. Tin coating has never been a favorite of mine as I don't think they last that much longer than the plain drills. I do like carbide tipped drills but they are expensive and hard to find, however there are some jobs that only they will do. I have a lot of Hanson drills as they are resonably priced and have a good service life. I stay away from any drill made in China as a general rule, even though I am sure that that there are some made there that are good. Buy Made in U.S.A. and you will have a decent drill IMHO.

[StrawHat]

What mtgrs737 said about overheating is correct.

I would guess the #1 cause of dull bits in the construction field is due to spinning the bits too fast and overheating them. Nice and slow, they cut and don't get dull.

As to fractional, alphabetical and numerical bits... it is all a numbers game. Each one is a different scale for the diameters.

The machinists on the forum can explain those.

[JSnover]

Thor,
If you buy fractional sizes it'll keep things simple but you won't have as many options. I'd get one set of each, all in HSS, that way you'll have every hole size up to half-inch covered. Cobalt is better but they'll cost more and they're not indestructible. For really hard stuff, buy some carbide-tipped drills. If you feel like spending even more money, get some solid carbide bits but use them carefully. They're brittle, so they're easy to break and the cutting lips can chip pretty easily - drop it on a concrete floor, might as well drop it in the trash.
Buy american if you can but I've had good luck with drills from eastern europe lately.

[No_1]

Gentlemen,

My .02 worth: The key to long drill life is coolant. There are many drill/tapping fluids on the market. Some are specific such as aluminum only and some are general purpose. It only takes a drop to do the job. On larger machines there is a coolant pump that supplies a constant stream of fluid that runs back in the tank. For smaller machines like the common home style drill press or a hand drill the squirt bottle of fluid will do the trick. Speed is a factor of bit life but on some metals you need speed. Buying "made in the USA" is sometimes a good sign of good products and the bonus is we support our own economy.

Invest $80 in a product like this : http://www.drilldoctor.com/product.asp?specific=106 and you will never have a dull bit. Those who have skills can sharpen a bit on a bench grinder just as well as a man with a drill sharpening machine but if it is easier to skip the learning curve by purchasing the sharpener.

High speed steel (HSS) is a good general purpose bit where you cannot go wrong. Carbide, carbide tipped and colbalt are good for their intended applications but if you break one off in the piece you are drilling you are just about as screwed as you can be and if you can't get all the pieces out (none embeded in the wall of the drilled hole) you will have problems re-drilling or tapping that hole.

R.

[scrapcan]

No 1,

Good advice. I have seen some amazing things done with cheap jobber HSS bits. An machinist friend was very good at sharpening and setting the angles based on the material and rate of feed he expected for the materials being drilled. He did it by hand, but having 50 + years of tool grinding probably gave him an edge that most of us will never have.

I worked a as glazier for a short time while in college and he also sharpened our glass drill bits for us. that is another topic all together. But coolant/lubricant is just as important (can't beat turpentine for drilling glass).

[Red River Rick]

Invest $80 in a product like this : http://www.drilldoctor.com/product.asp?specific=106 and you will never have a dull bit. Those who have skills can sharpen a bit on a bench grinder just as well as a man with a drill sharpening machine but if it is easier to skip the learning curve by purchasing the sharpener.

One of the first tests I give our new apprentices is to sharpen a drill by hand. If you can't sharpen a drill by hand, how do you expect to machine anything.

Those drill sharpening gismo's are OK for sharpening pencils, that's about it. Most of them "DO NOT" provide enough clearance, but rather grind radialy.

The biggest problem with drill failure is two problems:

1) Not enough spindle speed (turning to slow)
2) Not clearing out the chips often enough (too deep of a peck)

A simple formula to calculate the spindle speed for drilling, using HSS drills is 4 x the cutting speed divided by the drill diameter. The cutting speed for Mild Steel is about 100, so 4 x 100 divided by say 0.125 (small drill) = 3200 RPM.

Cutting speeds for other materials can be found in most Machinist's Handbooks as well as off the net.

Coolant should be used whenever possible, cutting oil if available. Maximum depth of peck would depend on the diameter of the drill, a good starting point would be approx. 20% of the drill diameter.

As some of the others have mentioned, solid carbide drills are great when used on "RIGID" machines (CNC equipment). They don't fair so well on conventional equipment and drill presses.

RRR

[georgeld]

RRR:
Great post.
Thor: www.wholesaletools.com, or MSC.com ask for their big books and study them.
you'll know more then and they'll mail 'em free.

You'll want to get DoAll brand HSS bits for general drilling. They're about the best quality
bit made at a reasonable price.
Get a set of each: fraction, numbers and letters to half inch and bigger one's that
you'll use most often as a starting point.

Any you'll be using on blade's get carbide bits and a good fine cut wheel rated for
carbide tools. and never ever use it for anything else. SO it'll keep a perfect face.
You'll need a wheel dresser for that too.

When I was in the shop we sharpened all our tools and bits down to about 1/16th.
was as fine as I could see even with 23y.o eyes and big mag glass on the grinder.
I got pretty good at it, but, shop closed down in '67, I've seldom had need, or tools
to do such grinding since so I'm far out of practice.
But, know afew facts. You can shrink, or enlarge a hole by the angle on the bit.

Get one of those constant spray coolant set ups for about $30-80 depends on your
'needs. Some are air powered, others electric.
I started my machist trade in the drilling dept. We drilled everything of all size's. From #80
the smallest bit made, to 5" on a huge radial arm press and everything in between.

From soft gummy aluminum, plastic, pure teflon, silver, titanium and all kinds of steels.
After two yrs drilling holes I was more than happy to transfer to a lathe. They closed down
before I got to the mills though. AND I developed an ulcer from the tight tolerance's
full time in two more yrs and went to a big turret lathe about half inch slop. Big enough
it had it's own overhead powered crane.

Coolant is the real trick AFTER good sharpening of GOOD quality bits. Dont' feed very fast
and don't ever put any pressure on the bit. IF it won't cut with a little weight, it's not
sharp enough. The way I was taught to drill. Soon as the cutting comes out of the hole and
starts to raise, pick up, drill in a steady light pumping motion. You don't want a full
curl to the cutting. Neither when drilling on a press, nor on a lathe either. When half
the hole is drilled I've had the foreman have me pull the bit out and if it was too hot
for his fingers, he'd chew ass for over heating the bit and parts. Aluminum and soft
stuff gets hot quick, when it does, it's gonna gum up the bit. So don't let it get hot.

Hope this helps a little. Like shooting, drilling takes a lotta practice to do it right. All the holes'
we drilled had to pass pin gage inspection too.

Good luck,

[calaloo]

A Drill Doctor is well worth the investment. It is not a run-of-the- mill drill sharpening jig. It uses a diamond wheel to grind the correct clearance and even grinds split points. Nickle bits are almost as hard as carbide without the brittleness. everyone should have a few left-hand bits. Broken off threads can often be backed out by drilling them with a left-hand bit.

Bill

[Buckshot]

............MightyThor, my suggestion would depend upon what you're going to be using them for, and how. I have a 29 pc fractional set in the top drawer of the workbench, and they're used for general stuff. I've had them a long time. I think I paid $49 for them. They're Hansen's. For typical homeowner deals and used in a drill motor I'd get some straight HSS bits. Probably bright finish (un-coated) and jobber length. They'll probably be 118*. I prefer 135* split points, but the others will get the job done.

BTW, most coatings on drill bits are for industry and NOT for the homeowner, or maybe even the hobby machinist. Another factor is that when you sharpen them, the coating is gone. Industry can make great use of them. Optimum conditions (coolant, right coating for the right material, correct speeds and feeds etc) make them do what they're supposed to.

I do have lots of coated bits, but NONE of the sets I've bought were specially coated, and the coated ones weren't bought because they WERE coated

................Buckshot

[JIMinPHX]

High speed is good for general purpose use.

Cobalt is softer, but takes heat a little better.

Carbide is very hard & very heat resistant. It is the only choice for drilling hard materials (like a saw blade), but it is brittle & expensive. Carbide bits are not for everyday use.

Coatings, like TiN or TiCN are helpful in abrasive materials like cast or other materials where additional natural lubricity is needed.

118 degree is the traditional drill point angle.

135 degree points are less likely to hand up & dig in at the end of a through hole, but they like to skate around when you try to start them.

A split point removes the likelihood of the drill bit skating around so much. They also generate less heat in some materials, like stainless.


There is also another angle to worry about, but you have little control over it unless you are grinding your own points. It is called the clearance angle & normally ranges from 91-120 degrees as viewed from the point end of the bit. On a split point bit you can’t see the clearance angle. Reading that angle & grinding your own points is a whole story in & of it self. With copper & brass it is fairly important to have a clearance angle nearly 91 degrees so that the bit will not dig in & hook up. Copper & its alloys love to have a bit dig into them, especially if you are not dealing with the harder heat treats. Stainless & aluminum both like very positive clearance angles, near 120. Plastic likes clearance angles that are positive off the scales as well as dead sharp edges. Most other materials are somewhere in the middle. More positive angles are preferred for hand drilling because they require less drill pressure.

There are different types of bits for wood. Paddle bits, or wood borers are usually the first choice. They are the flat-headed ones with a big point in the center & two smaller points at the edges of the cutting surface. They are cheap, fast & make nice clean holes. If you need to cut a hole that goes off the edge of the wood a little bit, then you want a Foristner bit, which has a big round head at the cutting surface. Believe it or not, high speed twist drills that are made for use in steel can be ruined by drilling wood because they can get too hot. Twist drills are OK for occasional use in wood as long as you don’t go too fast for too long, but if you need to punch a lot of nice holes in wood fast, buy a real wood bit.

For plastic, I’ve always used twist drills that I reground with very very very positive clearance angles. The paddle bits may work well here too, but I haven’t tried them. Here too the enemy is heat. Drilling many types of plastic can produce enough heat to ruin high quality twist drills. I’ve used carbide on plastics in some production jobs. With many plastics the material will spring back & give you a hole that is smaller than the drill bit that you used. This is especially true with a drill bit that has a dull margin (outside edge).

Fractional drills are the most commonly available. Their only limitation is that they have a minimum difference in size of 1/32”. If you need a hole that is in-between fractional sizes, then you need to go to letter or wire size drill bits. Some taps specify letter or number (wire size) drill bits for their pilot holes. Other than that, you can use fractional for most common uses. Some sizes cross over. I seem to remember that an “E” bit is actually 1/4". If you start with a fractional set, then add a stray letter or number bit as needed for special uses, then you should be set for 99.99% of what you will run into.

Spindle speeds, lubrication & coolant all matter too. If you spin a bit too fast, you will overheat it & ruin it. if you run it too slow, it doesn’t work efficiently. If you lubricate it, it will work better. If you add flood coolant, you can push it a lot harder with good results. To oversimplify it, put a drop or two of oil on a piece of metal when you start drilling it. Increase the drill speed until the oil starts to smoke, then slow down a little bit & use that drill speed. Stop to clear chips & add another drop of oil every 1/2 of a drill diameter of depth that you drill. Again, that was an oversimplification & not exactly the perfectly kosher way of doing things.

Do not use lubrication in cast iron. Just go slow.

If you are drilling something like stainless that generates lots of heat & is famous for destroying drill bits, then go very slowly & use flood coolant of some type. In a machine shop, they have water-soluble oils that recirculate for stuff like that. It the outside world, running a garden hose to keep cool water pouring on the stainless as you drill it gets you by. With stainless, cooling is more important than lubrication.

[scb]

Thor, What I did was years ago I bought a descent - not the best, 3 in 1, 115 pc drill set. When I brake or burn one up and have to replace it I'get a Tin coated Chicago-Latrobe. Alot of the drills in these sets will very seldom if ever get used, but it is nice to have them around. The ones you do use you'll use alot that's why you get good ones. Buying them one at a time doesn't hurt so much. My $.02

[floodgate]

I do the same as scb, but got TWO of the 115-piece sets, and marked one, for BRASS, after "breaking" the cutting lips very slightly to an eyeballed 1* negative rake; this also works better on hardwoods and a few other materials; the other set is marked "STEEL" for more general use. I have other, individual sets of fractional, number, letter and metric sizes, but the two 115-piece sets live in the cabinet under the lathe and get the most use. I try to keep up with replacing dulled or broken ones, or doing them up on my Drill Doctor; but I do see some empty slots.

floodgate

[Johnw...ski]

My suggestion is that you stick with HSS the cobalt drills are ok but that split tip they all seem to come with is much more difficult to sharpen. Cobalt drills don't do well with a regular point because their web is thicker. As far as letter, number, and fractional, it all depends on what you are doing and what you need, a good machinest would have them all. Oh, and don't forget metric size drills if the other three aren't enough.

When I was in the business and my eyes were better I could sharpen driils, even the small ones, with the best of them. I still don't think much of those drill sharpening contraptions. Get yourself a good grinder with good flat square edged wheels and use it for sharpening only, not grinding anything and everything. Get yourself a few cheap drills and buy a drill gage similar to the picture, there are also much cheaper versions that will do fine, and practice sharpening your practice drill untill there is nothing left. Sharpen it, try it on something, if it cuts fine, if not examine it with a glass and try and determine why it won't cut. The point angle may be off and will show up with a glass, there may not be enough clearance and will show up as scuffing behind the cutting edge.
Touch up your drill untill you get it to cut and grind it flat and sherpen it again.
I promise you will get good at it.

Hope this helps and good luck,

John

[bohica2xo]

As a Tool & Die maker that finished his apprenticeship in 1980, I will add my 2 cents.

I recomend the Drill Doctor for anybody that drills more than a few holes a week - in anything harder than wood.

I can still hand grind a drill down to about .093 dia. I can make a .250 drill cut .265 if I want it to. And I own a Drill Doctor. It is simple, convienient & repeatable.

If you want to make a 118 degree split point, no problem. Want them 140 degrees? OK. Want to add a split point to a standard drill? Go for it. A very flexible machine. Diamond grinding wheel, so it will sharpen a carbide drill.

Most machine shops have a drill grinder of some type. A nice Gorton or Black Diamond will cost about 4k. Many are now using the Darex at about 1800 bucks. Hand grinding drills is still done, but not at the volume it used to be.

B.

[mstarling]

The Drill Doctor does work ... and it will save many, many dollars in drill bits. It does what it advertises to do.

[georgeld]

Most drill grinders I've seen will put the tape on them just find.

What about getting the back clearance angle on though???
Thats the most important parts about grinding drills.

[Bret4207]

I'm just an amateur shop monkey, but I love my Drill Dr. I know it doesn't do all the tricky stuff I learned in machine shop class and read about in the books, but it takes the bits my kids used or I found at an auction and gives me a place to start. If I need a special or really sharp bit I have a good start. And since my eye sight is..... well, lets just say I'm not 19 anymore, it sure makes things easier.

I bought 2 drill index sets, the Chiwanese type years ago. The plan is as the bit's break, get lost, etc they'll be replaced with good USA made ones. I just don't have the money to put $300.00+ dollars into a good set. MSC sells good ones individually as does Brownells and lots of other places. Last I checked MSC had about the best prices and delivery.

[georgeld]

Bret:
I've found: www.wholesaletools.com or wt.com beats MSC by a bunch on prices. THey've got a bunch of drill sets, plus loose one's.

[alamogunr]

Bret:
I've found: www.wholesaletools.com or wt.com beats MSC by a bunch on prices. THey've got a bunch of drill sets, plus loose one's.

Not Bret, but where do you go to find drills in all the sponsored links that pop up??? I tried a couple of the links but they just sent me to more links.