walt_in_hawaii wrote:Sorry, I think I will have to (respectfully) disagree with you.
I buy lots of carbide inserts and high speed steel tooling for my mill and lathe, and at first everyone falls in love and spends the extra money for the pretty yellow titanium coated tooling... but after awhile, you start to notice that the coating makes absolutely NO DIFFERENCE in tool life, and you end up buying just the regular bits instead of the expensive coated ones. Now, for coffee beans undoubtedly there will be a huge difference, its a much softer substrate being cut. However, its still tool steel on the cutting side... I would challenge anyone to produce the data which shows it makes much of a difference in longevity.
What DOES make a huge difference in tool life is the aggressiveness of the cutting edges, their cutting geometry. Their shape and how much metal is in the edges vs how much metal is left after accounting for relief angles and how aggressively they 'point'.
I feel like you're answering your own question.
As you hypothesize, the coating likely makes a difference with a soft substrate, so there is an advantage is having the tools coated (which adds to cost). Now, this is likely not an advantage for a home user, but it can impact in commercial settings, which you have to remember pretty much all 75mm burrs are meant for commercial settings.
In addition, like you mentioned geometry makes a huge difference. Some geometry's will be more difficult to produce, as some will have significantly tighter tolerances than others, which also drives up cost.
Just like tools, you can have multiple bits for the same general purpose that widely vary in cost, however, they may perform very differently for various tasks as some will be better suited for certain tasks than others.