I think the purpose is less about finish (you get that with different belts) and more about geometry. I've seen a lot of guys use it for grinding convex blades, or even for shaping handles.
I'm sure you are right that you can achieve similar results with a slack belt, but I think this reduces the learning curve quite a bit, and gives you a bit more consistency.
I have a Hardcore Products Cushioned Platen.
http://www.hardcore-products.com/section.php?xSec=11 Second unit down.
This sweet attachment has a serpentine belt that you can adjust the tension on for grinding and sharpening knives. It does help with the Bump Bump when using those belts, The Origin of this was a idea from Ken Onion and developed with Rob Frink of the KMG fame.
At the time I worked with Rob on a prototype of a unit for the Hardcore/Burr King grinders. I am not a machinist and we were unable to get it to work smoothly so I sent it back to Rob.
A few years later Randy of Hardcore worked with Ken Onion and was successful in making the Cushioned Platen for the Hardcore.
I don't know if this will work on a Burr King? As mentioned this unit is more about shaping than what kind of finish you can get. I get the same finish weather Grinding flat or con vexing.
The primary things I use this con vexing Platen for are,
after heat treat I take my Flat ground culinary Knives and convex the blades with this unit.
I get a nice even tension from the adjustable belt and it allows me to use any weight belt and get the same consistent Convex grind on the blades,
Work's great for handle sculpting and I get great results using it to sharpen my customers knives.
I generally run it at 25% power on my HC grinder with a 1.5HP Variable Balbor motor.. This speed with sharp new belts does a excellent job in allowing me to also control the amount of Convexing and flats I have in the particular knife model I am making at the time.
It seems that people ether love them or hate them!
I love mine! :7:
Laurence
www.rhinoknives.com/
