Wondering about grinding speeds

[M.FREEZE]

My questions about grinding speeds are as follows:
I am using a 1.5hp variable speed BaderIII

1- do hollow grinds and flat grinds react the same way to belt speeds?
2- should belt speeds change as the grits get smoother?
3- do certain steels react differently than other steels when the same belt speed is applied? For instance, do 3V and 154 CM react to grinding the same way when identical speed, grit, etc is applied.

I am just curious. If there is a more efficient way than what I currently use, I'm interested.
Thanks, Mike.

 

[Frank Niro]

I found flat grinds use up more of the same sandpaper per size than hollow grinds do. If you go to finer belts, it was a common thing to decrease the belt speed but many of the new type belts don't seem to require this be done.Definitely almost every type of steel works differently in how it grinds and finishes. There are huge differences between many and a type that's not as easy to work may be chosen because the need to favor a certain characteristic of the steel. Frank

 

[jhl]

Mike,
I am interested in the replies to your three items, plus I would also like to know how optimizing belt life plays into the speed, grit, material equation. I would like to think that there is some archived advise on this, but I haven't figured out how to chase all of that info down. I am rather new here and yet to learn how to navigate my way through all the info and find what I want. Got started making knives two years ago with the help of a friend, and I have spent a lot of time reading bladeforums. The quality and the quantity of the information on this forum is a giant resource, and the forum members are especially patient and kind to the newcomers.
Thanks,
Jim Luckett

 

[Grinder1]

Tho I mostly convex grind my blades....I cant comment on the first part of your inquiry. I generally slow my belt speeds as I move up the ladder of grits. My edge is defined usually at 80 grit and I move up thru to 320-400 grit depending on the blade. My speed for the most part is slower but often I may speed up a bit to clean grit lines off. Working with A-2- CPM3-v, AEB-l and 5160 I would tell you that YES, certain steels react differently to grinding speeds. CPM3-v requires good belts and I often grind it slower then the other steels I use. Often a belt that is at the place of not grinding on 3-v will grind okay on the other steels.

 

[fumbler]

I don't hollow grind so I can't comment on the first question.

As you progress in grits you often have to slow your speed down. Finer grit belts generate heat faster. That's especially a bad thing post heat treat. You don't have to slow the belts down; instead you can just make lighter and faster passes but when you do that you can lose some consistency and control.
Like Frank said, the type of belt, not just the grit, matters too. Trazact cf belts seem to generate less heat than conventional belts of the same grit. That could be a combination of less surface area in contact along with the "tread" pattern pulling some air against the steel.
Having a variable speed grinder makes life a lot easier, especially when you're starting out. You'll find that as you gain experience you won't have to slow down quite as much.

Different steels do require different handling. The higher the wear resistance the slower you have to go or you'll burn up the steel. Some steels have weird properties. CPM 3v seems to glaze over easier than s35vn at the same grinding speeds at higher grits. I recently made a knife out of 1095 and it was a piece of cake to grind and finish compared to what I had been working on (3v and CPM d2).