Reprofile a Ratmandu with a convex edge

[maximus83]

I have a Ratmandu that has barely been used, has a high sabre grind with a convexed edge.

What would be best approach if I wanted to entirely change the edge geometry to v-grind? Bad idea? Or do I just take it on a super-coarse stone and start scrubbing until I have a flat secondary grind, same as anything else?

 

[ahoward2k]

I had some knives with convex edges from my work sharp, now I'm using a guided system and I just grabbed a 120 stone, set my relief angle and went to town.

 

[maximus83]

Hmmm, this is unusual in the maintenance forum to get a low response rate. Wondering if that means that trying to reprofile this thick blade, by hand, is just a bad idea freehand and would take too long, be too error prone? Hence your approach of using work sharp or guided systems. I have to think that using powered or guided system with quality diamond stones would sure make this go a lot faster.

What guided system do you use, and have you ever done a major reprofiling like this that would involve completely changing your grind and removing a LOT of metal?

 

[Obsessed with Edges]

If you're already considering using a scrubbing technique, freehand on a stone, I don't see any reason not to do it that way. A scrubbing technique will definitely be faster than if trying it with a guided setup, with it's small hones, restricted stroke length, etc. Chances are, a scrubbing technique will still induce some natural convex on it's own; the back & forth of the blade on the hone will be accompanied by a little bit of rocking of the blade.

You don't necessarily have to pursue a perfectly flat V-grind, for that matter. Just keeping the held angle a bit lower and limiting the rocking of the blade will produce a shallower, thinner convex, which can be a great cutting geometry. It's how most of my knives end up, and I've never been disappointed with it. And once you get accustomed to that scrubbing stroke, maintenance of a shallow convex becomes very, very easy on a stone.


David

 

[HeavyHanded]

Hmmm, this is unusual in the maintenance forum to get a low response rate. Wondering if that means that trying to reprofile this thick blade, by hand, is just a bad idea freehand and would take too long, be too error prone? Hence your approach of using work sharp or guided systems. I have to think that using powered or guided system with quality diamond stones would sure make this go a lot faster.

What guided system do you use, and have you ever done a major reprofiling like this that would involve completely changing your grind and removing a LOT of metal?

If it were mine I'd strip the coating and grind the primary down on a belt grinder to reduce the cutting bevel width and thin out the overall stock thickness. Then reset the cutting bevel to a V. It would be less work and the knife would cut like a demon.

Other possibility is to strip it and work the convex further up the primary and not try to convert back to a V.

Just resetting the existing bevel to a V should not be all that difficult even by hand - yes, just get out your favorite coarse stone and scrub away.

 

[maximus83]

If it were mine I'd strip the coating and grind the primary down on a belt grinder to reduce the cutting bevel width and thin out the overall stock thickness. Then reset the cutting bevel to a V. It would be less work and the knife would cut like a demon.

Thanks, I think what you described here is what I actually want to do. This thing is extremely tough, but it's like a sharpened pry bar and despite the nice edge, it doesn't slice well at all so it's not a very good knife at ANY task. I know that's heresy here at BF--I'm a big carbon steel lover myself and it's definitely the in thing to heap praises on the Ratmandu. However in my perspective: it's way too small to do any useful chopping at a fast rate, or even much splitting beyond about a 3.5" diameter. And then if you try to use it for the 90% of other ordinary knife tasks you'd use it for most of the time, including slicing and chopping for food prep, or fine detail tasks, it just ranges from mediocre to bad due to the thick primary grind and edge geometry. I've tried a number of simple tasks with it, ranging from splitting (it's fine for that, if you keep the diameter small), to chopping (terrible--don't even bother), to ordinary slicing and food prep (terrible). I think it's a well made knife and good quality steel, nice handle design, etc. So I get why people like it in some respects, and agree. But when I get a knife like this, I get it to actually USE in backpacking and it needs to be versatile across a range of tasks, and for that, it's actually pretty lame as shipped in its factory condition.

I think this is really simple, it boils to just two issues and you've touched on both:

• The "tweener" size of this 5" blade, it's just an inherent compromise sized knife where you're trying to make it a generalist between large and small knives. And while it can work in some respects, it ranges from less-than-optimal to terrible for all ordinary uses that I have for larger and smaller knives. There's nothing that can be done about that aspect, other than use a slightly larger "compromise" knife such as my ESEE 6 which is better at all tasks, large and small, than this knife is.
• The primary grind is unnecessarily thick for a knife this size, turning its optimal functionality into serving as a pry bar (which is something I would almost never use a knife for), and seriously compromising its functionality as a cutting tool. I think we could fix this issue by using an approach like what you described, which sounds like it is indeed going to take a belt grinder to evenly, quickly and consistently, rework the entire primary grind.

 

[Twindog]

I'm with Heavy on this one, but it should not be hard to convert the convex edge to a V edge, although a lot depends on how obtuse the convex edge is and what angle V edge you want to replace it with. When I want to reprofile an edge, I usually use a belt grinder to do the heavy lifting, and they follow up with the Wicked Edge to perfect the edge geometry.

As a general rule, the width of the edge is more important to slicing than the angle of the edge, so a full blade reprofile like Heavy is talking about will give you a lot more slicing performance. But that kind of regrind is difficult to pull off without it looking like heck.

You might ask Josh at REK or some other regrind artist to do the work. I've never liked the heavy, rough blade coatings of Busse and kin.

I don't see a 5-inch blade as being a "tweener." It's pretty effective for a fixed-blade generalist. It won't chop, but it gives you a lot more power and leverage than a folding EDC. For me, 5 inches is perfect for a general-use EDC. For a chopper, I'd go longer, depending on the use, but then you lose a lot of comfort in carrying it.

 

[ahoward2k]

I use a tech studios k02, I reprofiled my kabar to have a much lower relief angle, and it took about 45 minutes with a 120 grit stone. but the angle is true and the edge is a uniform width across the whole knife

Hmmm, this is unusual in the maintenance forum to get a low response rate. Wondering if that means that trying to reprofile this thick blade, by hand, is just a bad idea freehand and would take too long, be too error prone? Hence your approach of using work sharp or guided systems. I have to think that using powered or guided system with quality diamond stones would sure make this go a lot faster.

What guided system do you use, and have you ever done a major reprofiling like this that would involve completely changing your grind and removing a LOT of metal?

 

[hhmoore]

Unfortunately, Busse-kin blades have a reputation for being nearly indestructible, and a warranty to back that up. While the warranty is great, it encourages people to do some really stupid things with their knives. Accordingly, the knives are built toward the durability and hard use side of function, rather than general use and effective cutting. I can (sort of) see the benefit in a big chopper that will see all manner of use/abuse; but it just doesn't make sense (to me) in smaller knives.

 

[kwackster]

There is a real good knife hidden in that overbuilt tire iron, and if it were mine I would most certainly regrind it to a full convex zero edge, or have it done by one of the highly skilled service providers on this forum.
The SR101 steel is so well heat treated that it can easily take an apex in the 30 degrees inclusive region to stay on the safe side, or around 25 degrees inclusive if you don't plan to abuse it too much.