Cutting tools – Moh’s scale of hardness

CNC – Mohs scale of hardness and cutting tool materials
When a cutting tool cuts a workpiece, it is basically a scratching of one material by another. The tool, which is the harder material, scratches the workpiece, which is the softer one.
Scratch hardness is defined on the Mohs’ scale of hardness (developed by Frederich Mohs, a German geologist, in 1822), on which Talc is 1 and Diamond is 10. It was originally developed as a measure of the relative hardness of minerals.

Hardness technically is the ‘Resistance to permanent deformation’. The Mohs scale is relative, while Vickers, Rockwell, Brinell and Knoop are absolute measures of hardness. Mohs is a measure of scratch hardness, while the rest measure indentation. There is however a direct correlation between the two, because scratching involves two actions: 1. Pressing the the harder material into the softer one – the indentation. 2. Moving the harder material at the indentation depth – the scratching.
Scratch hardness of some cutting tool materials and other common materials:

It’s Mango season, once again
It’s mango season, and there’s at least one deliriously happy person in the world – that’s me. Mango is one of my favourite fruits. In India summer, between April and June, is mango season.
India has around 280 varieties of mangoes, and is the biggest mango producer in the world, accounting for 40 % of the total. These are of course just the cultivated ones, and doubtless there are many more wild ones (which tend to be small, more fibrous, not so sweet) growing in forests. The 280 varieties are spread over the country, and you don’t get all varieties everywhere. In Bangalore we probably get about 20 types.

I have this strong religious belief that I have to eat at least one mango every day during the season, and that the Mango God (since there wasn’t one, I had to invent one to explain my addiction to the fruit) will be extremely angry if I miss even one day. There are days I’ll eat upto 5 fruits, and on my bucket list is the feat of eating 10 in a single sitting. I plan to try it while sitting in the lobby of a hospital so that, based on my condition after this, I can either be quickly wheeled into the ICU or can walk out singing.
And yes, I eat mango the way it should be eaten, as demonstrated by our close cousin in the picture below.