Drill Bits - What is best?

[mikehaugen]

Cobalt can be sharpened on a regular grinding wheel, carbide requires a "green" wheel.

 

[the old grind]

Not to be a smart-arse 'cuz I retired as a tool grinder, but +1 to all said above, esp using a drill press with cobalt (or carbide ). I can only add that:

Coatings are perhaps misunderstood by most. As a rule on cutting edges they work by reducing friction/heat/wear as the chip rolls up the flute. Grinding it away from the relief portion of the cutting edge comes at little to no sacrifice since only 'over-feeding' the driill typically allows contact there. (say by power-feeding Z-axis, etc).

A drill bit (exact term subject to nomenclature debate elsewhere..) is only as good as the quality its edge. A cheapo HFT bit can be sharpened nicely, but likely comes poorly done OOB. HSS stamped (honestly) on a shank is a good start if in doubt as to what's being looked at. ('carbon steel' is for wood.) That said many home/workshop sharpeners have the same debilitating shortcoming by 'indexing' the tip to the wheel from a point somewhere up the flute. Bits with a different rates of twist will then not sharpen to the same relief angle, thus to the same ability to cut.

A 'Drill gauge' is but a few bucks at the supply house, and learning to use it can make even 'snag' sharpening work once you learn to check your work as you get the hang of it. (not rocket science) There's how-to's all over the net and 3/16" & up sizes are pretty easy. If you don't 'thin the web' after a few resharpens of a bggie (>1/2"?), expect to have to 'pilot' a hole with something smaller before going in.

 

[whistlepig]

Carbide has to be sharpened on a diamond wheel.

 

[the old grind]

A 'green' wheel is silicon carbide vs the aluminum oxide of typical vitreous ('rock' to me) wheels. They break down quite a bit during use and throw a lot of dust. We often use them to sharpen cemented carbide tools where HSS and carbide contact the wheel, usually when grinding a secondary relief. It's kinda old school nowadays but a must have for the home shop. (We 'clean up' edges with a fine diamond hone before making chips.)

On the CNCs we use various diamond (carbide) and CBN (cubic boron nitride) wheels (HSS) with a 1/8" or so thick band of grit mat'l around an aluminum hub. Program offsets account for wear as wheels break down and are re-dressed between batch runs. New wheels, or dressed dimensions, are entered into a wheel file on the controller. Vitreous wheels are a mess with coolant systems and don't hold square nearly as long. (Don't get me going, I just do mill & lathe work in my home shop now & really miss the old days of making sparks .... : (..)

 

[Pete Judd]

Depends what you want to put holes in. I use almost always use forsner or brad point bits for the wood that I butcher. Some carbide, some HSS. Don't put holes in steel much anymore.

 

[whistlepig]

It boils down to the dressing of the stones. With a diamond faced wheel against carbide there is little or no dressing. Diamond on carbide is a slow process. With the softer stones more dressing is required. As the softer stone degrades so does the quality and crispness of the sharpening. A degraded (grooved) stone will not give a clean and even edge. Some of the good softer stones on high speed steel cut much quicker and clean themselves better without dressing. A much better choice for HSS. But not for carbide.

 

[charlz]

A cheapo HFT bit can be sharpened nicely, but likely comes poorly done OOB.

I was walking through Lowes the other day and saw Skil brand 'titanium' drill index marked down at least half price. I opened the set and it looked like the bits had been sharpened by a two-year old with an angle grinder. I ended up opening 3 sets because I just couldn't believe that all of them would be that bad.... but they were.

 

[newbury]

Conditions have to be right for cobalt. Proper speeds, feeds, and rigidity. Putting a cobalt drill bit in a cordless drill will be sure to disappoint. Cleveland, in my opinion, makes the best HSS drill bits.

I'm sure glad I didn't read that BEFORE I drilled my bucket. I started with a new HSS and it was futile. Ridgid cobalt bits and a DeWalt portable made it a breeze.
/edit - once I got the jury rigged set up done

On a side note I've found chainsaw chain oil works well as a lubricant, especially if you have to drill upside down. It tends to stick to the bit.

 

[sal64]

high speed steel is best for reg steel. cobalt is to hard has a chance of chipping.titanium wount make a differance its only good for highspeed milling and drilling plus when you sharpin it the coating is ground off the tip.

 

[sal64]

Can the cobalt bits be sharpened? I know lots of folks like their Drill Doctors.

yes reg grinding weel.