Bad heat treat? trouble with a certain blade.

R

RDog

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Jul 28, 2011
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Do any of you have a certain knife that gives you trouble sharpening?

I have a Rat 1 folder and overall its one of my favorite knives. The trouble I have is it seems to hate to give up and get sharp.

I sharpen blades two ways these days, with the sharpmaker and with sand paper/pad setup. I learned that some of my blades responded to the sandpaper very well while others love the sharpmaker. Thin blades (most folders) go to the sharpmaker and thicker blades like the sandpaper/pad setup.

With my Rat 1, shortly after getting it I noticed if I sight down the spine, there is a slight bend or bow to it, and there is a slight distortion. I can't think of any other cause than a bad heat treat which would cause this. I imagine that a poor heat treat could also make the blade harder or softer or maybe both in different places alone the length of a blade, than was planned.

So the trouble I have with this blade, does it sound like its the heat treat that is the issue? I mean the same technique that gets all my other knives (except my swiss army) hair shaving sharp fails on the Rat 1. I can get it sharp, and by the sharpmaker, but its a long battle with special attention, instead of just a certain number of strokes.

Recently I decided to convex the edge and with sandpaper, got it pretty good, but not as sharp as I'd like. So I went back to the sharpmaker and in my struggle to bring the edge to where I want it thought I'd ask the question.

So does anyone else have a certain blade that gives them trouble? Do you blame the heat treat?
Anyone have the same problem with the Rat 1?

I've really wanted to pick up another one as I don't think the line of knife could all have this sharpening issue, and even with this trouble I love the knife, just hate how it really makes me work for the edge I want.
 
If the blade is warped that doesn't necessarily mean it's a bad heat treat in terms of hardness/toughness. Blades are prone to warp during the quench.

However a crooked blade may be difficult to sharpen because you have to make small adjustments to the angle. A sharpie and a magnifier can tell you if there are areas you're not apexing due to this.

Otherwise, a bad heat treat usually results in the steel being "mushy" or "gummy", meaning it forms a large burr very easily and it's hard to get it to snap off. Or it might be too brittle and the edge microfractures from the pressure of sharpening. That would probably prevent you from getting to the very highest levels of sharpness but I doubt it would prevent it from getting to paper slicing sharpness. But try lightening the pressure and see if that helps.

Also, knives often have bad steel on the very edge from overheating when they grind the edge. This does not mean the heat treat was bad, but you have to sharpen away the initial edge to get down to good steel.

The other thing is if the knife has a very thick edge. The bevels would be very wide and it takes a lot of effort to apex the edge. The grind could also be uneven, so you either have to re-profile until its even or adjust your sharpening technique to match the unevenness.

Sharpie and magnifier are your friends to see what is actually going on.
 
^ this
It is very difficult to do a good job on an edge with a warp. You can get there by accommodating the warp but that's tough, easier to grind away enough steel that the cutting edge forms a straight line or nearly so when viewed edge-on. And yes, the first bit of metal on an edge is frequently overheated and no good, even knives from quality mfgs. I recently went through this with a knife from EKA that has a warp - once the cutting edge got straightened out it takes and holds a fantastic edge. Keep in mind, the bevels will not look even - they thick and thin depending on where the warp is. If the warp is real bad I'd consider sending it back.
 
Robs92XJ pretty well nailed it, on all points (blade warp = non-issue, so far as heat treat goes; edge itself might need to have some marginal metal ground away; edge is probably too thick). :thumbup:

Only thing I'd add is, if you tried the convexing with sandpaper on a mouse pad, try something firmer for the backing. Sandpaper can perform in hugely different ways, depending upon how firm (or not) the backing is. Try the paper on thin leather over hardwood, or try balsa backing, or even put the sandpaper directly over some good hardwood backing, like oak or maple. The latter suggestion (hardwood backing) is becoming a much more attractive option to me, personally. I wouldn't mess with the Sharpmaker at all, at least for now. I'm betting the edge angle is too thick, and re-bevelling to something more acute can work wonders, most of the time.
 
Thanks for the imput, I figured I'd have to just "grind down high spots" on a good flat stone at some point. A good magnifier has been on my want list for a while as well.

I'll try sandpaper on a hard backing to see where that takes me, hopefully it will work and I will not need to buy a stone.
 
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