Inadvertent Re-curve Problem

Col Defender

Col Defender

Joined
Nov 11, 2011
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This pictured knife is an example of a problem I end up with occasionally. Without meaning to the end result includes a re-curve that I did not want. Obviously I have a technique problem in the final stages of grinding. Anyone else experience this? I guess I just need to be more aware of what I am doing and pay closer attention before it is too late. Any specific suggestions? (I do Damascus, and 1084, convex grinds on a Sears 2 x 42)



It's not been a problem with customers - they actually seem to like it, but I would like to get this under control.

Thanks!
 
The only way is to scribe a center line and...don't hit it. A variable speed grinder does help in slowing the rate of removal as approaching the edge, but isn't written anywhere that we can't use old good files for precise work.
 
I have two thoughts; grind to a pair of center lines as already mentioned and bring your edge off the back of the blade in the choil area or add a sharpening/Spanish notch. How are you sharpening your knives? I suspect that is where your troubles are coming from.

Bob
 
Col.-

Is this happening only during/after heat treat? Or, do you believe its an issue with your grinding technique?

That knife looks to be heat treated(??). If so, and if that "re-curve" occurred during the heat treat process, it is likely a result of the natural cooling/grain formation process during the quench. Although I stayed in a Motel 6 last night, I'm no metallurgist:p, but I'll bet Stacy(and others) will be along to offer a proper explanation of this phenomenon.

-Peter
 
This happens to me very easily as I dont grind with a platen or fixture or anything. The way I avoid it is to use very light pressure once I get close to the edge. Use a strong good light and frequently check your dimensions. Also as mentioned grind slower speeds towards the end. Pay careful attention to how your are releasing pressure after you make a pass. My problem is always inadvertently contacting the side of the belt opposite of where I have my eyes focused on. One method that has helped me to spot overgrinds early on is to use a higher grit belt in light pressure smooth passes. This will really highlight where your grinds are inconsistent and in danger of an overgrind.
 
I'm sorry for your frustration, but selfishly-really glad I'm not the only one who has this problem ;). I noticed the same issue on some of my knives as I went up in grit during my final finish grinding. I THINK this was/is my problem, may not be yours:

Plunges still cause me anxiety. So, when they're pretty darned good, it really gets me worried about messing them up. When thinking about the recurve issue, I think it was a result of my hesitance to smoothly move in and out of the plunge area. I'd linger a bit longer or just end up working that area more than the rest of the blade as I focused on keeping those plunge lines nice. Then, before long, I had that recurve section forward of the plunges. To solve it, I find I have to do better at multi tasking. When I'm thinking about the plunges, I need to pay just as much attention to the rest of the contact points on my belt. I've also changed how I grind just a bit. I do flat grinds on my platen, but as I get closer to the final grind edge thickness, I convex the edge on a slack belt. If I don't linger too long (again...) towards the plunge, I can keep things straight. If I focus my grinding too much at the plunge....right back to recurve...

I think some of my tendency about this is getting the cutting edge as far back to the plunge as possible. I need to remember that the cutting edge is realistically going to be forward of the plunge a little ways if I've rounded them/feathered them into the grind (edge thickness at that spot is thicker than the rest of the blade). The more I try to get the same cutting edge all the way back, the more recurve I end up grinding because there's more material towards the plunges that I have to remove. I hope that makes some kind of sense. And not sure that's your cause or issue, but figured I'd share my experience with my poor skills :).


Jeremy
 
Grinding bevels on a slack belt is going to make a curved edge. As you try to get the plunge right, it is taking extra away about an inch or two away. You really need a flat platen to do good bevels.
 
Stacy E. Apelt - Bladesmith said:
Grinding bevels on a slack belt is going to make a curved edge. As you try to get the plunge right, it is taking extra away about an inch or two away. You really need a flat platen to do good bevels.
Click to expand...

Is it essential that said platen be glass? My Sears grinder has a metal platen which I use often, though not usually when grinding a bevel. But I am about to try. Thank you Stacy.
 
If you have used the original platen quite a bit I suggest you check it for areas of wear. A straight edge with a light will do a good job.If there are areas of wear you will have to overlay the platen. That's where the glass (pyro-ceran) over lays came in. A lack of correction will mean some very odd blade grinding. What happens is the belt will actually slow down in these spots and produce strange metal removing.
Frank
 
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