If you’re using a belt grinder, here are some setup tips that can influence the final result:
Results can vary based on the grit and stiffness of the belt as well as how far it hangs over the platen and the angle of the knife itself.
You will get different variations based on the belt grit, stiffness, how much it overhangs the platen and the angle of the knife. The only way to figure it out is to experiment and see which results you prefer.
Start by determining where the grind line should end. Establish it when you start grinding and stick with it throughout. When professional knifemakers grind their bevels, they usually mark the spot where they want their plunge line to terminate, so they can line it up with the edge of the belt.
It’s a good idea to start grinding right at the plunge line and then work your way back toward the tip. If you make mistakes with your plunge line at the beginning, it can be difficult to fix later, so grind a fairly shallow bevel so you know exactly where your grind is. Then you can come back up the angle and work your way back up the knife.
Once the bevel has been established, feather the belt in from the edge side and lay the bevel flat on the belt.
Plunge lines should be symmetrical from one side of the blade to the other. As stated in the previous hint: know where you want your bevels to be. Establish them exactly in the same place on each side and leave them there.
Hang your belt off the edge of the platen, which is the surface that supports your belt when you flat grind your knife. Center the belt so that its edge and the edge of the platen on both sides are the same, then grind away. All things being equal, you get a straight and crisp plunge line by following this step.
By adjusting the tracking knob on your grinder, you can change the shape of the platen.
You can get different plunge lines with different belts. Ceramic belts tend to produce either very sharp edges or very long sweeping curves (hanging the belt off by at least one quarter inch), but they're not so good for that in-between line where it hangs off by perhaps ⅛ of an inch. In that case, your basic aluminum oxide belt would be better for in-between curves.
There is no functional difference between soft and hard plunge lines. The harder ones are faster and easier to do. This has some advantages in a production environment: you don't have to worry about changing the tracking, so you can just grind away. The soft ones take a little more skill to get right, but if you finish them by hand, they're much simpler.