Is it carbide?

I went out to my favourite second hand shops today and among the things I got in a bundle was a 20mm slot drill, 105mm long with a chip on each cutting corner. For a small piece of metal it feels rather heavy. Is there a way to tell whether an unmarked bit is HSS or carbide?

I don't think tooling grade tungsten carbide is magnetic?

Tony

I think measuring the density is the easiest method The density of tungsten carbide is 15.6 gm / cc. The density of HSS is 8.1 gm / cc. The easiest way to measure the density is by using Archimedes principle. Weigh the item on kitchen scales and make a note of the weight. Then put a container of water on the scales and zero the scales (Or note the reading.) suspend the item with a piece of cotton and immerse it in the water. It must be fully immersed but not touching the bottom. The increase in reading is the weight of water displaced. So as the density of water is 1 gm / cc the weiight of the item in air divided by the weight of water displaced is the density.

Edit.
        I just noticed Tony's answer. I also had that thought but on testing the carbide tip I had was magnetic but not  as much as HSS.

Les.

Edited By Les Jones 1 on 27/02/2016 17:39:47

If it's heavy and chipped rather than worn, I would say almost certainly carbide.

Neil

Tungsten carbide is usually sintered using cobalt, which is magnetic, as a binder.

Rod

I just tried a few solid carbide printed circuit board drills on a big magnet. There are mildly magnetic but not as much as MS or HSS. An easy way to test is to try grinding them on a normal grinder. If they are carbide then the wheel will hardly do anything, but a green grit wheel should grind OK.

My immediate thought reading Les' suggestion was that it was wrong! Archimedes says the loss in weight of an object immersed in a fluid is equal to the weight of fluid displaced. I'd never thought about the weight of a container holding the fluid, but surely that wouldn't change? As I was just making breakfast in the kitchen it was a matter of but a moment to fill a mug with water, pop it on the digital scale, tare it, and stick my finger in. To my initial surprise the indicated weight increased! The reason why niggled all morning but came to me in the middle of treating some wood with Cuprinol. An interesting experiment, both actual and mental.

Edited By John Haine on 28/02/2016 13:45:58

That's cos you were pushing the water down. Try pulling yer fingy out quickly, It should show lighter than original.

Regards Ian.

If you have a spring scale you can weigh the bit when fully immersed and the difference between the immersed weight and the weight in air will give the weight of the displaced water. The air weight divided by the displaced water weight should give density.

Martin

Put an unimportant bit against a white grinding wheel, if it glows red but doesn't grind away then its carbide.

Hold a modest metal weight, say about 4-6 ounces, on the palm of your hand. Now immerse hand and weight in water.

Does the weight feel lighter, heavier or the same?

Neil

No, just wet!

Clive

Hi John (H),
Did you leave the end of your post the way it is to prompt more discussion on the subject ?

Les.

Les, indeed I did! I looked up Archimedes Principle on Wikipedia and like everything else I've read it explained it in terms of the reduction in weight of the suspended object. I'd never seen the version you quoted and at first it seemed unlikely, but experiment doesn't lie.