Shouldn’t Diamond-Tipped Tools Just Fall Apart Under High Stress Use?

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Yes, Diamonds are the (usually) hardest substance available for a variety of industrial applications.

Yes, they are found on everything from the tips from dentist’s drills, to masonry saw teeth, to the surfaces of angle grinders.

Is a diamond tip really that much more effective in most applications?

For extremely hard jobs, what’s preventing the diamonds from falling out of the much softer material they’re embedded in?
Wouldn’t the fail point be wherever it’s weakest?

In: Engineering

I mean they do? I’m a dentist and the burs I use go dull pretty quickly. Most are single use, and even the ones that are designed to be sterilized and reused have to be replaced fairly often.

The diamonds fall out and break pretty quickly because technically they’re just glued on (resinoid bond) or embedded in the tool.

There are lots of other types of bonds that we use for abrasives, one of the most prevalent being the vitrified bond which heats an abrasive and bonds the grains together. You see this in AlO3 often (corundum) which is a 9 on the MOhs scale of hardness as opposed to a 10 for diamond.

I’m not sure what answer you’re looking for, but due to the hardness, diamonds are in fact quite brittle and therefore fall apart during use. Vitrified bonds take advantage of the grain falling apart to reveal new cutting edges, but I’ve never seen a vitrified diamond cutter.

There are several ways to measure how robust a material is.

You’ve touched on one of them: hardness. This is the measure that diamond excels at. It measures how well a material resists being scratched, or how well it can scratch another material. When you try to scratch one material with another the harder material will have almost no damage, while the softer one will see all of the damage. The harder the hard material is the closer to zero damage it takes. This same thing happens when cutting, where the cutting or grinding, where you want the cutting or grinding tool to take as little wear as possible, so hardness is the thing you care about.

There’s also strength. That’s the measure of how much force it takes to break something. That’s the measure by which an object will fail at its weakest point. Generally the tools you mentioned aren’t breaking due to forces, so strength isn’t the quantity that needs to be as high as possible. Note that strength may be measured in terms of the strength of a material as an intrinsic property (e.g. “steel is stronger than brass”) or as an extrinsic property of an item (e.g. this rope has a strength of 100 lb).

Another quantity is toughness. A tough object is the opposite of brittle–copper is tougher than ceramic. Tough materials can withstand impacts well. More formally, toughness is a measure of how much energy it takes to break a substance.

Then there’s stiffness, which measures how much a material bends when you apply a force to it.

Very often materials that are hard are not very strong, tough, or stiff. With a cutting tool you want the bulk of the tool to be strong, tough, and stiff, but the surface you need to be very hard. To achieve this the tool is often set up with two materials, such as a steel tool with a titanium carbide coating, or steel with a diamond coating. This gets the best of both worlds.

> For extremely hard jobs, what’s preventing the diamonds from falling out of the much softer material they’re embedded in?
Wouldn’t the fail point be wherever it’s weakest?

That’s exactly what happens. The softer metal wears down, the diamonds fall out or break. But regular tools do that to (this is why you have to sharpen knives). Diamond tools just do this slower.

It’s important to note that diamond tools aren’t “sharp”, they don’t cut stuff like knives. They abrade stuff like sandpaper. There’s a bunch of of extremely hard rocks gouging out material as they get moved against the piece. As the diamond tool gets worn down new diamonds are exposed, unlike non diamond tools that rely on a cutting edge.