Very shallow hollow grind.

jdm61

jdm61

itinerant metal pounder
Joined
Aug 12, 2005
Messages
47,357
I was told by a manufacturer/vendor, Millit, that they do VERY shallow hollow grinds with a cup wheel on a CNC mill. They told me that they can go these grinds as small as .005 "radius" That does that mean. Would it be .005 deep at one inch wide? I am confused. :confused:
 
found an interesting little article on modern machine shop about cup wheels. You figure they are finishing prosthetic hip joints to a very fine degree of precision, I imagine knife blade shapes would be a walk in the park.
 
You can do a flat grind with a cup or a facemill easily by going across the work flat. I mill clips like this. But if you set the work on a little bit of an angle relative to the plane of the cup/facemill you'll cut a shallow hollow. This isn't a radius, it is a conic, so you'll have a hard time describing it with a radius value, I think it might be a Rho? It will have a larger degree of curvature at the ends and flatter towards the center.

I'm sure they mean .005 across the width of the grind. And they're probably guestimating.
 
so they put an abrasive cup wheel in a toolholder in a spindle and use it to grind?
 
Metalhead0483 said:
0.005" radius? Functionally wouldn't that just be a flat grind? I don't see the point...
Click to expand...

It would take a 50" wheel to make a .005" hollow across one inch. That would be pretty typical for the flat side of a Japanese knife, it serves a few functions including sharpening flat to the stone.

If applied to a double bevel knife with 1" bevels, 3/32 stock and .005 at the edge before sharpening, the difference between a flat grind and this grind back 1/8" from the edge would be .026" vs .032" thickness. That is functionally different, 20%.
 
So it would be about the same as what what your 48" platen will do, but with the slightly "flatter" middle that you were talking about? ?
 
jdm61 said:
I was told by a manufacturer/vendor, Millit, that they do VERY shallow hollow grinds with a cup wheel on a CNC mill. They told me that they can go these grinds as small as .005 "radius" That does that mean. Would it be .005 deep at one inch wide? I am confused. :confused:
Click to expand...

I'd say that depends on the diameter of the cup wheel they're using, and/or the width of the blade that's being milled. It'd probably be best to just ask the vendor to clarify. ;)
 
It took a while to get an initial response , so in the meantime............
knife to a gunfight said:
I'd say that depends on the diameter of the cup wheel they're using, and/or the width of the blade that's being milled. It'd probably be best to just ask the vendor to clarify. ;)
Click to expand...
 
Metalhead0483 said:
0.005" radius? Functionally wouldn't that just be a flat grind? I don't see the point...
Click to expand...

Not a .005" radius - a .005" arc height over a 1" chord. That calculates to a radius of 25.02"



I have posted a tutorial for grinding the urasaki on a Japanese knife back by doing the same sort of thing on a contact wheel. Just turn the blade at a slight angle from perpendicular to the belt and it will grind a wider hollow segment. This males a 10" wheel grind a hollow similar to a 50" wheel.
 
Last edited:
You must log in or register to reply here.
Back
Top