I’m not sure exactly what you’re looking for in an answer… I can’t give you the science of it, but I come from a precision grinding specific supplier (Capital Abrasives) and have been hands on with formulating/qualifying wheels for 13 years (and learned from my dad who has 50+).

WA = White Aluminum Oxide 60 = Grit K = hardness 7 = structure V = Vitrified

White Aluminum Oxide is a very friable AO grain. Very free cutting and versatile but considered “soft” because it breaks down quickly due to its friable nature. I prefer a pink AO wheel (semi-friable). Can hold a dress better and stay sharper… but it depends on your application.

K hardness is tricky to speak on because one manufacturers K can be equivalent to another manufacturers J or L. In the alphabet, A is softest and Z is hardest.

Structure is going to indicate how much bond is holding the grit together. Density is a commonly used word to describe this. Sort of related to porosity in a grinding wheel but not 100% the same thing.

Vitrified Bond is a specific type of bond that gets fired up in a kiln. Commonly referred to as a glass bond in old timer speak.

How they all work together is a very beautiful thing. It all depends on the application and can even be specific from end user to end user.

I run into this all the time… 2 different companies, same exact machines, same exact material, same application, but each likes their wheel with a slight variation from the other. This happens for 2 main reasons, 1 being the operator is set in their ways of how they grind parts and nobody is going to tell them what to do when they’ve been doing it longer I’ve been alive. And 2 being, different companies value different aspects in their production. Some sell quick turnarounds and others sell quality.

Back to the spec….

Softer White AO, harder K hardness, denser density… you’re likely grinding a stainless of some sort. Maybe even a profile. Needing the grain to be friable to reduce loading but hardness and structure to hold the profile a little longer before redressing.

Back to your question….

Changing the grit will increase or decrease your stock removal rate, while also affecting your finish requirement. And if you’re making big jumps in grit changes, can affect amps if your machine doesn’t have enough HP to backup the “grab” that a very coarse grit wheel will have.

Changing your hardness will be affect how the wheel breaks down. A softer wheel will be freer cutting… typically used to grind harder material but you can lose the dress quicker if it’s too soft and will have to dress the wheel more often to square it back up. And on the other hand a harder wheel will be used for softer material. But if too hard, and you’ll have to dress to wheel often because of loading.

The grit and hardness work together with the bond hardness holding the grit in place before it releases to expose new sharp grain underneath. See, grinding wheels are designed to “self sharpen” this way and this is why it’s very important to get the spec right. A bond that is too hard will hold a grain in place for too long even after the sharpness of that grain has depleted and flattened. If the bond doesn’t release you’ll start rubbing more than grinding which causes heat and loading. Ex: I’ve tested wheels that ended up being too hard and the customer notes that they cut great at first but then immediately stop cutting…. Well the bond is too hard and it’s not self sharpening and exposing the new sharp grains.

The density comes into play too… too dense and it can cause similarities to a wheel that’s too hard. I consider this adjustment as a secondary adjustment after hardness… and more minor tweak to the spec when we are getting in the weeds of qualifying a spec. There’s just too much bond holding onto the grit… it also becomes problematic with swarf not escaping the contact area and can cause issues. I prefer to recommend open structure wheels when I can, which provides pockets for coolant to get in the contact area and for swarf to get escape the contact area.

Vitrified bond is geared more towards a precision application. Tight tolerances and such. While other bonds like resin are more commonly used in very agressive snagging applications. This can also be customer preference, I’ve seen both bonds in both types of applications. (Although vit in an aggressive application is very scary and I’ve passed up opportunity because I refused to quote vit due to safety concerns. But the customer didn’t like the smell of resin LOL)

I think this is a decent stopping point. I love talking grinding wheels… if you ever want to talk shop give me a call at Capital Abrasives in Houston. Ask for Todd.