Are there better drill bits than cobalt?

[gspd]

The speed, pressure and cutting oil you choose have a lot to do with how long the bits last and how well they cut.

[ME 109]

I'm with Curt on learning to sharpen a drill bit by hand, and his advice on the requirements for grinding wheels.

imo, a drill bit moves through two axis when sharpened by hand, and most 'drill sharpeners' use one axis resulting in a larger (flatter?) contact area of the cutting edge.
Probably the hardest thing with sharpening by hand is keeping the outer points of each cutting edge level with one another. (at whatever angle)
please feel free to correct my interpretation.

[Roy Gavin]

I still got most of pops Dormer brand HSS drills - must be over 50 years old now. They have a black oxide finish.

Still got his can of Trefolex? cutting paste too - a half pound tin looks like it will last two lifetimes.

They get an occasional sharpen using a Eclipse Sharpening Jig, a neat little item which wipes the bit along a sheet of wet and dry as it wobbles along, and this gives the correct back cut.

I dont have the skill or wheel to do them by hand, but that is how I have seen the pros do them.

To save the other bits I buy a packet of #30 double ended bits and drill a pilot hole with them.They dont get sharpened.

The secret to drill life is slow speed , plenty of pressure and lube and keeping the drill cutting, not spinning, and this is easier if you drill a pilot hole first.

[gspd]

No formal machinist training, I rarely drill pilot holes first....... hmmm....
I thought that's what a centerpunch mark was for.
I usually set the belts on the drill press for the slowest speed and use a lot of pressure.
And I'm not stingy with the cutting oil.

Is it correct to assume, that if you're getting a nice even 'coil spring' shaving coming out of the hole, that you're doing it right?

With some metals I get chips and chunks of shavings instead of a 'spring'.

I haven't yet found any bits that survive things that are rough and have been heated treated,
like the remains of a cotter pin in a tierod end hole that you heated red hot (to get the nut off) after it's been in salt water for decades (or one Quebec winter).
The split in the remaining section of cotter pin prevents any drill from going straight, and usually the bit breaks when it snags on the hardened outer walls of the original hole.
Pin punches sometimes work, but they don't last too long either when using them for that.

I don't know if I'm explaining it right,
but if you work on rusty cars a lot, I'm sure you know EXACTLY what I mean.

Peter Egan could write an entertaining column on removing old cotter pins.
Maybe he already has?

[Jean]

Curt is right-on. Learn to sharpen bits by hand. quench frequently.
If you drill aluminum a lot, you'll find the bit-angles need to be different from what works best for steel.
Always use some sort of lubricant.
When you are drilling big holes, drill pilot holes, this keeps the load off your bigger expensive bits as there is less material to remove at one bite.You also get a better hole! (Really!) More metal to remove at once means more pressure, more load on the cutting parts hence more heat and possibly chipping the cutting edge.
Buy bits larger than 3/16 inch or so from an Industrial supplier...get the smaller ones separately, but get the best. The small ones ARE expendable.
The Black&Decker store usually has a discount bin of smaller bits...good place to get a bunch that will do good general purpose metal working, and not so expensive that you will weep when you break one.

[The Veg]

I can't seem to get a year out of a toaster oven anymore!

Really? I have a DeLonghi that has been utterly perfect for eight years! It includes convection & dehydration settings, comes with all sorts of grates & pans, and is compact outside yet big enough inside to take a 10" pizza. I've baked cookies & breads, roasted small things, and even made jerky in it. It's prob'ly my favourite kitchen accessory. I never knew I could get so enthusiastic about a toaster oven!

[ME 109]

We are not allowed to sharpen drill bits at my work, because it is modifying the tool.
We go through a LOT of drill bits. Mainly drilling aluminium up to 1-3/4" thick. Often drilling out broken steel bolts in the ally. Usually gets messy drilling out a broken bolt and a die grinder is often used to finish the job by removing ally from around the broken bolt.
Hole sizes up to 1-1/2" are drilled with no cutting fluid because most of the drilled holes are filled with ally mig weld.

A pilot hole helps when drilling larger holes because it centres the larger drill bit and prevents contact of the centre of the larger drill bit, which is the least effective area of the cutting edge.

A perfectly sharpened drill bit will give two even sized swarf twists.
Not perfect will give two unevenly sized swarf twists.
Or one swarf twist and chips.
Chips only is from a not quite right sharpening. The angles of the flutes may be the same but the angle of the cutting edge is off. (difficult to put in 'my' words)

Usually mild steels are higher speed (the smaller the faster) and stainless is low speed with lube.
When I used to sharpen large drill bits from say 5/8" up to 2" I used a simple jig that allowed me to measure the outer cutting points and get them even. Then the angle of the back cut needed to be correct as well.

A drill press as opposed to a hand drill is the best way to prolong the life of a drill bit.

Usual disclaimer.....all imo.

[Ken in Oklahoma]

Those sharpening wheels get expensive. Question is....is it worth it to invest in a sharpening system with it's costly abrasives, or just buy new bits? I hate the throw away system. But hell, I can't seem to get a year out of a toaster oven anymore!

Editing:
I made the following post before I read Curt Henry's excellent post. I decided to let my post stay rather than deleting it. Maybe it might be helpful to somebody. I'll defer to Curt about making the grind flat rather than curving it the way new bits are. I've often wondered if flat wouldn't work as well.

I have a Drill Doctor that I shouldn't have bought. It's fiddly to use and the diamond wheel is coarser than I would like to have for drill bits. I used it a handful of times initially then went back to doing what I did all along, sharpening drill bits on a grinding wheel. By hand.

I reccommend this to anybody contemplating buying a Drill Doctor.

It's not so hard to do. I do the grinding on a "fine" grit wheel, usually using the edge of the wheel, but sometimes using the side. (I know, I know! I stay mostly out of range and press very lightly.)

The first thing to do is get a virgin large bit and look at the tip. This is what you're aiming for. To grind the bit you will hold it at the appropriate angle to the face of the wheel. Then lightly touching the cutting edge of one flute to the wheel you will sort of roll the bit down such that the back edge of the flute is shorter than the cutting leading edge. Then you will rotate the drill bit 180 degrees and grind the next flute.

You probably won't get to the point where you're pumping too much heat into the drill bit but I keep a glass of water handy to keep the bit cool. If you turn the tip of the bit blue or straw color while grinding it, you've probably screwed the temper up. You'll have to grind the bit back to harder steel. That's when you really have to keep the bit cool with water.

But how do you keep the two cutting flutes the same length and how do you avoid changing the angle of bit at the tip? The short answer is that you don't. I tend to grind the tip of the drill bit to a sharper Vee angle than it came with and sometimes one flute does more cutting than another. You'll know if one flute is longer by watching the curls of steel rise up the drill bit when you're drilling. For 99% of the drilling I do my not-quite-precise grinding job is good enough, and a hell of a lot better than a dull drill bit.

The process is, of course, cheap. But the convenience of being able to touch up a drill bit when you discover it needs it is nearly priceless for me.



Ken

[Major Softie]

We are not allowed to sharpen drill bits at my work, because it is modifying the tool.

Unbelievably stupid. Sharpening is not modification, it's maintenance. If sharpening is modifying, then dulling is modifying, so the tool is modified the instant it is used.

Yeah, I know, you already know all that. Where do you work that has this stupid gotta-have-been-made-by-a-lawyer rule?

[George Ryals]

If an employee is working on tools (sharpening a drill bit) when his job is producing product, then he is not making money for the company.