Re: Drill Bits
Most of the "Cobalt" drills I have seen on the market are simply coated. True Cobalt drills are quite brittle and should only be used in soft materials such as Aluminum or Zinc castings etc. A true Cobalt drill will fracture on the margins if used to drill steel, its very brittle but surface drilling such as that required to remove rivets would be OK.
Having likely tried every drill on the market I recommend Cleveland Twist drills to anyone that asks, yes they are expensive...yes you may have trouble finding them except from machine shop suppliers. Another good twist drill is Chicago Latrobe, also expensive...you get what you pay for.
They are worth the money if you do a lot of drilling but may be more drill than you need for home use. They aren't magic but they hold an edge no matter how far you grind them back, most drills have soft cores and once you lose that initial edge they wear quickly if resharpened a few times.
I still have my original set of Clevelands in a complete letter/fractional/number set from 25 years ago, it cost me $180 back then including the case and each drill came individually packaged. Except for a couple of number and 1/16" drills that were broken they are all still there and have been resharpened dozens of times. I split the tips and backcut them myself on a bench grinder, it just takes some practice and a calibrated mark one eyeball to get them perfect.
I also have numerous cheapo drill sets that get used around the house for stuff that I could care less if they get broken..I seem to inherit them when the original owner wears the initial edge off them. I throw out the worn ones after a few sharpenings since they won't hold an edge after that. But if you do a lot of metalwork and need accurate sized holes invest in a good set of Chicago's or Clevelands...they might last you a lifetime once you learn to sharpen them yourself.
