Drill bit materials question

from

The most common bit material is high-speed steel. There are still the odd cheap carbon steel bits out there but the price difference is not enough buy them over the better HSS bits. These days there are also tungsten carbide, titanium and cobalt bits, all designed for lasting longer and drilling harder material. They are all more expensive than HSS bits but will last considerably longer. Tungsten carbide will last approximately 3 times longer, titanium will last approximately 6 times longer and cobalt is hard enough to drill stainless steel and should last 10 times longer than HSS bits. Buy the type of bit according to how much you expect to use them. For the average home shop the HSS bits are fine.

There are five common lengths associated with metal cutting drill bits; stubby, jobber, two lengths of aircraft bits and extended bits. Stubby bits as their name implies are shorter the standard jobber bits and are intended for harder use situations because there is a much less chance of them breaking. In comparison with a ¼" jobber bit which is usually about 4" long a stubby bit is only 2-1/2" long. Aircraft bits come in 6" and 12" lengths and extended or "long boy" bits are usually 18" long.

Brian W

That page is down, I'll try later. Thanks for putting them in order of life expectancy. The cobalt bit definitely cut into that bolt, but when I went from starter bit to larger, it bound and chipped, I took it back. I don't know what the B&D power points are made of, but I was impressed with it. Of course, my other bits weren't sharp so bad comparison.

The Brand new titanium bits didn't do a thing though. Isn't there a good type and a crap thin plated or sputtered (?) coated type that wears out quickly? I got 2 sets cheap from one of those Cooper Tool venues.

Thanks, Mike oh. Happy New Year - good luck and health in 2004

Mike, sorry I didn't transcribe that URL correctly - too many "w"s. I'll try again:

Brian

HSS does most jobs, but it's very important to use it properly when drilling difficult materials. Use the correct RPM and even more important, always enough coolant. If the drill gets too hot, it's gone. At the cutting edge, temperatures of several hundred °C are easily achieved. Drill chips must never be colored from heat. I drilled once 120 12mm holes with a standard HSS drill into 10 mm 18/10 stainless and it was still sharp afterwards.

Coated drills (a.k.a. Titanium drills) consist usually of a HSS base material and a very thin layer of Titanium Nitride, or similar compounds to reduce wear and friction, applied by sputtering or CVD. But if the base material is low quality, the coating doesn't help much. A good rule of thumb is: if it's cheap it won't last long.

Cobalt drills are a high grade HSS, with large amounts of cobalt.

Solid tungsten carbide, eventually coated are the best you can get, they last very long if treated well, but are brittle and unnecessary for most applications.

Drills made of pure cobalt or Titanium do not exist.

Andreas R.

"Active8" schrieb im Newsbeitrag news: snipped-for-privacy@news.east.earthlink.net...

"Andreas Rutz" snipped-for-privacy@deletethis.gmx.ch

I don't know much about the newer coated twist drills, but historically speaking the earliest form is high-carbon steel. Though these are considered bottom of the lot today, with careful use, and a sharpening system that you commit to, they would still work fine for mild steel. They also are a consideration where breakage is a concern--because broken carbon-steel bits can be annealed and drilled out, making their removal easier than for bits of more sophisticated steels.

HSS was developed 1880s to its general introduction in machine tooling around

1900. I don't have a feel for how much you should be concerned when HSS produces blue chips, but you can run it to do so. It's introduction revolutionized machine-tool design, because it could be run faster/hotter.

And as pointed out, cobalt bits are one form of HSS. Sometimes in sales language generic HSS is designated as M2, and cobalt as M42.

Carbide (tungsten carbide) tooling came in in the late 1920s--"Carboloy" was one of the main brands. It became the production tooling standard (not just in twist drills), replacing HSS in that regard. In metal lathes, for example, the carbide toolbit inserts used today have generally replaced the former general practice of grinding full-solid HSS bits--making for a more "throw away" rather than hand grinding, skill-based technology.

For occasional use on unsophisticated steels, any of the above will suit once you get familiar with the toolbit's feeds/speeds, lubrication (carbide usually is not lubricated), and sharpening. Also understand that "twist"drill is not the be all and end all of making holes. Frank Morrison