Drill Bit Types & Characteristics
Thanks & a tip of the hat to Ed Wingate RATCB for this data
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High speed steel is a relatively cheap hard tool steel used for most ordinary purposes. It cuts wood plastic and other easy materials well. The bits can bend so they are very durable for hand drills. The steel is tempered so if they overheat they are softened and ruined.
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Tungsten carbide is a very hard material and can cut hard materials like glass, rock, stainless steel. It is pretty heat resistant and will not de-temper. Difficult to sharpen and it is usually braised to a steel backing. Its weakness is that it is very brittle and can crack easily. It is often used in wood working tools where cracking is not a big problem with the soft wood. Very expensive compared to steel. In our case, carbide tools stand up to FR-4 phenolics very well where tool steel dulls fast. Almost all printed circuit board drilling and routing is done with very high speed tungsten carbide tools. Carbide is often used in metal working lathes where a small tool edge can last a long time in a well controlled situation without being subject to impact damage.
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Cobalt alloys are super hard like carbide but less likely to shatter or break and not terribly expensive. But when they do, the are almost explosive and send shrapnel all over the place. Cobalt actually gets harder as it heats to about 500F. Cobalt cutters and drills are used where cutting very hard materials is needed and the cutter has to take some abuse without breaking. It can be used in hand drills and is popular with machine tools. It has high wear resistance and is difficult for a normal person to dull. Sharpening really isn't an issue since the tool is probably worn out by the time it dulls. They do fatigue over time so best to replace them on time. When I cut 6-4 titanium with cobalt tipped blades, the blades do not dull but the teeth eventually fall off.
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Titanium-nitride is that gold coating you often see on tools these days. It structure is supposed to be harder than diamond. It is vacuum deposited in a thin coating rather than a tool material. It mainly helps chips slide off the flutes. Nice for, say, soft aluminum, titanium, copper, and other materials that like to stick to and gum up tools. It also adds corrosion resistance and holds cutting oil. It can be thought of much like the coating on Teflon cookware in its function. Since it is so hard, the coating is super durable. Even my most used cutters just show small wear of the coating at the very cutting edges.
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I think the best bang for the buck is Ti-N coated Cobalt. It is strong and the tools will last a very long time. You do have to be a bit gentle with them but they will not dull and they can cut anything from wood and plastics to titanium and stainless steel alloys. 6% aluminum - 4 % vanadium - 92% titanium alloy will easily overheat tools due to the very poor thermal conductivity. It likes to grab and gum tools, and is super hard (designed to defend against high-velocity bullets...). Ti-N Co tools are just about the only thing that can touch it. Otherwise it's ECM, water jet, and plasma torch. With all the hard alloy tools, safety glasses are NOT optional.
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July 19, 04. Drilling Copper/Brass & other soft metals. Original poster: Ed P. "Also, and this is one of those tricks of the trade, use a stone to make a .015" or so flat on each cutting edge of the drill that is parallel to the centerline of the drill and runs at a 90 degree angle (perpendicular) to the work piece. That will keep the drill from "catching" when breaking through the bottom of the material on brass and other soft materials. Drills modified in this manner will still work fine on any other material, but will save you a trip to the emergency room of your local hospital to re-attach severed fingers! I hope no one here drills metal without clamping it down first, at least "after the first experience"! I have drills ground as you described and they work quite well in acrylic as well as brass, for the same reason. Tap Magic - Useful on just about any metal known to man, includes brass. I frequently use WD-40 for brass because it's not as messy and easier to clean up than "Tap Magic". Tap Magic works on stainless, Inconel, Monel, Beryllium, Molybdenum, Aluminum, Magnesium, Copper, Bronze, Brass, Titanium, Cobalt, Nickel, Cast Iron, etc. Ed Wingate RATCB.
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6-14-11