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HDC -- High-quality "normal" twist drills today are made from several different alloys, but they can be pretty-well divided into two families: "high speed steel" and "cobalt high speed steel". The cobalt high speed steel will withstand higher temperatures than standard high speed steel, and for this reason is often preferred for drilling holes in stainless. Standard high speed steel drills can be "bright" (no special finish, just bare metal), "steam oxide" (smooth black), or have any of several different platings or coatings including "chrome clad" (satin silver looking), Titanium Nitride (TiN), Zirconium Nitride, or Titanium Aluminum Nitro-something-or-another (TiAN). The coatings serve a useful purpose, but primarily in high-production use. For home shop use or even non-production commercial machine shop use, the standard high speed and cobalt high speed drills serve well. I've been really happy with the cobalt high speed drills (which have a slightly-to-moderately yellow/brown appearance) for almost everything, but some say that the cobalt high speed drills are more brittle than standard high speed. With standard high speed, I much prefer the steam oxide finish to the bright. Far more important than material or finish, though, is QUALITY, and the quality of the product is controlled by the maker. American or GOOD imported drills (from Japan or Europe) will cost a lot more than the bottom-of-the-barrel excuse for twist drills being sold in the dollar stores. But some of the dollar-store specials don't last long enough to drill a single hole in wood . . . they don't have a chance drilling into metal. So where do you get good drills? Well, if you can live with standard high speed drills, you can find decent drills at good hardware stores. They will usually be steam oxide "jobber length" drills with a conventional 118-degree point. To get better drills than those, you'll almost certainly have to go to an Industrial Distributor or mill supply house (including mail-order suppliers such as MSC, Travers Tool, Airgas/Rutland, and so on). These suppliers will handle the same steam-oxide standard high speed, 118-degree point drills as the hardware store, but will also have both standard and cobalt high speed drills with 135-degree "split" points. The "split" point has the web of the drill ground in such a way that a secondary drill point is created . . . the drill will start cutting metal amost immediately instead of having to PUSH the metal away from the drill's web like standard-point drills do. If you need to do much drilling at all, the split point is the way to go in my opinion. The one "common" source for split-point drills is Sears. The Sears Craftsman Zirconium-coated drills have split points and supplemental chip-breaker grooves in the point. They are pretty good drills, but I suspect it has more to do with the point geometry than with the pretty yellow coating. One big shortcoming with the Craftsman Zirconium drills: they are offered in a VERY limited number of sizes. The only old-fashioned "carbon steel" drills I've seen in years have been super-cheap trash that isn't worth the effort to bring home from the store. At the other end of the spectrum is the solid carbide drill, which is very expensive and will hold up in a manufacturing environment for a very long time, but they chip and break very easily and should NOT be used with hand-held drill motors. One final thing: high speed steel is sensitive to thermal shock and a great way to destroy a high speed steel tool is to let it get hot and then chill it rapidly. Dipping a high speed steel tool in water to cool it when grinding is a good way to overstress the metal, as is starting to drill a hole and then squirting a cutting potion onto it. John
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