small intersecting hollow grinds

F

floatlikeariver

Joined
Sep 6, 2006
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I have recently been working on an extra 12'' piece of O-1 I had lying around. I designed a killer contemporary fighter with hollow grinds (full main and half top) and ground the main edge first. came out super sweet. When I moved to the top edge, I could not follow the groove for $#!T. The blade was singing with a wierd high-pitched vibration, and like I stated, especially as I got closer to the intersecting of grinds, the contact wheel was dancing around and grabbing the blade and basicallly just man-handling me. Never had this problem in the past, although the last time I hollow-ground, it was on a thick, natural stone, water-cooled jewlers grinder. (this is my first on a belt) Needless to say, the blade is now junk for much else but testing my new tang stamp on. Any advice, helpfull tips, or co-miseration would be cool. :( :confused:
 
Is the grind on the top a true hollow grind or a kind of swedge? The reason I ask is because I am working on something similar to that now, but put more of a swedge or false edge on the upper front half. I did have somewhat of a trouble with the belts getting grabby, especially with the finer grits. Also heard the high pitched noise. I had to really lock the elbows in and lean into the grinder for extra stability. I got pretty frustrated, then realized I may be better off finishing with files, which is what I did. If it is a true hollow grind on the top, not real sure of the cure. I do think that part of the problem is surface area (or lack there of) in contact with the grinding belt as compared with doing the main hollow grind. It could just be the nature of the beast. :D -Matt-
 
I haven't done many peices like that myself, but I do mostly hollow grinds on my knives....
I would say that since the upper grind is going to be at a steeper angle, and have a narrower hollow/groove, you would do better to rough it in first while you have more material to work with and more to hold onto.
You also may try grinding the top bevel upside down. Keep the primary edge of the blade up. This will keep the wheel from biting the top edge of the spine so hard and causing the vibration. Similar idea to sharpening edge down on belt grinders.
And definitely run the grinder as slow as you can for things like this.
 
The top edge is a true hollow grind to be sharpened. Damn the luck, I don't have a variable speed grinder yet and it is pretty fast and not too steady. vibration in the finer grits too. right when it matters.
 
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