New to me Sheldon, question about HSS tools - Page 2
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  1. #21
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    With regard to making the vast majority of HSS tooling, as others have said, hand grinding is by far the way to go. Yes, it can take a little while to get a 1/2" square blank ground to the basic shape, but not that much time - and I'm guessing it would be much quicker than mounting in a surface grinder and making the many, many, MANY multiple passes that would be required. Only if I needed a super-precision shape would I go to the trouble of grinding in a SG, and then only after I had gotten close to the shape needed with hand grinding. And absolutely no way would I risk the destruction of the ways of a CNC to grind in that.

    One thing: be sure you are using the proper type of grinding wheel. Those "rocks" that come on the average bench grinder are way, way too hard. Ideally you want something around H or I hardness. Counter-intuitive, I know, but you will grind hardened steel much faster and cooler on a softer stone.

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    Quote Originally Posted by awake View Post
    One thing: be sure you are using the proper type of grinding wheel. Those "rocks" that come on the average bench grinder are way, way too hard. Ideally you want something around H or I hardness. Counter-intuitive, I know, but you will grind hardened steel much faster and cooler on a softer stone.
    Ummhhhh.. Takin' that to the extreme..and we were not MEANT to doo this, given how fast the friable wheels would git eaten-up...but ... 2d or 3d shift, fewer "eyes" about, work to git done, we'd often step over a foot or two and rough shape our Mo Max or Rex 95 on the "green grit" wheels meant to be used only for Carbolloy brazed carbides!


  3. #23
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    The interesting question would be how hard or soft those green stones were - not the grit, which presumably was silicone carbide or something like that, but the stone as a whole.

    As I'm sure you know, the "hardness" grade of a grinding wheel is not a function of the actual abrasive; various aluminum oxide stones can range from super hard to super soft, but it's all aluminum oxide. IIRC, the difference is in the bonding of the grit. A "softer" stone has a weaker/softer binder, allowing dull abrasive to slough off and fresh, sharp abrasive to be presented to the work - thus actually grinding a hard steel faster than a "hard" stone, where the abrasive gets worn down but stays stuck to the wheel. Or something like that - I claim no expertise, and may not be recalling the reasoning correctly ... but I do recall being astonished when I first learned that I needed a "softer" stone rather than a harder one for grinding HSS, and equally astonished when I tried it and discovered how much better and faster the softer stone cut.

    And of course, there is always the possibility of taking something to the extreme - if an H stone is better than an L, why not go all the way to something super-soft like an A? Because it will wear away too quickly ....


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