The Balisong Collector Reviews The Benchmade Model 31

This is the Benchmade Model 812, "The Mini AFCK."

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Benchmade never publishes production statistics, but dealers I've spoken to all seem to agree that this is one of -- if not the -- best-selling Benchmade models. There's a lot of reasons for that popularity. One of them, I suspect, is its size. Closed, it's about 4.4 inches long overall. The Mini AFCK is big enough to be useful, but not so large that it's inconvenient or uncomfortable to carry.

The BM42, 43, and 47 are actually fairly large knives. They're about 5.5 inches long closed. That's a pretty big thing to carry around. I have to confess that I don't always carry my favorite BM43. But I'm rarely without an 812 Mini AFCK.

Recently, Microtech introduced the Tachyon (to read my review, click on this icon ) . Closed, Tachyon is just under 5" long. It's smaller than a BM42/3/7, but some people may still find it a bit large for comfortable every-day carry.

Now, Benchmade has filled this gap with the Benchmade Model 31 Bali-Song.

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Closed, it's only about 4.25 inches long overall. But, there's still almost 3 inches of blade inside of it.

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If you find the Benchmade 4x Bali-Songs to long if even Tachyon seems a bit large, then you'll probably find the 31 to be the Bali-Song that finally get's a place in your pocket every day.

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As you can see in the picture above, the BM31 shares something other than a pocket-friendly size with its Mini AFCK cousin. The BM31 features a pocket clip for easy carry without a sheath.

At first, I was skeptical. The concept behind a pocket clip is quite simple. But, in my opinion, most knife companies have really bad pocket clips. Some are so stiff that it takes The Jaws of Life to get the knife out of your pocket. Some are so loose that the knife will fall out with the slightest brush. Some are so flimsy that they bend and break under even light use. Some are so poorly secured to the knife that they pop right off. And some have sharp edges that can cut your pants to shreds.

The clip shown on the AFCK in the picture above is one that Benchmade uses on may of their pocket knives. And it's an excellent clip. It's got just the right amount of spring. It's durable. It has no sharp edges. And it secures to the knife with three screws.

The clip for the 31 is thinner. In the pictures, it looks flimsy to me. And, it secures to the knife at only one point.

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But, I'm pleased to report that Benchmade knows pocket clips. The 31's clip is every bit a Benchmade clip. The edges are nicely finished. It's got just the right spring. It seems durable to me. And, the single point attachment isn't flimsy at all.

Oh, and if you don't like the clip, it's removable. All you need is a T6 Torx driver to remove the screw an the latch will come off easily. (Torx is a registered trademark of the Camcar division of Textron Corporation.)

Torx screws are widely used in automobiles these days. Torx is also being adopted rapidly in many other applications. So, Torx drivers are readily available in hardware and automotive parts stores. But, T6 is just a little small. T10 is the smallest Torx size that it's in common use. T6 boarders on being a jeweler's size. So, you'll probably have to go to a specialty tools store to buy a T6 Torx driver

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Not only is the clip removable, but it can go on either side of the knife. So, if you carry your 31 in your right-hand pocket or your left-hand pocket, if you want to carry the knife oriented with the latch forward or back, you can set your 31 up the way you want it.

The screw that secures the latch is rather small. The very name Torx sort of implies torque. Indeed, one of the touted advantages of the Torx screw head design is that it enables screws to be easily torqued to higher levels than the old-fashioned Phillips or Slotted screw heads would allow. That's great for larger screws. But, for a small screw like this, that feature can backfire. In fact, putting a Torx head on a screw this small is almost a bad idea. If you're not careful, the Torx head will allow you to apply enough torque to break the head right off of such a small screw. So, be careful.

Since it's intended to become your every day carry knife, the BM31 features a simple, but very practical, "utility" blade profile.

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This simple profile looks less "menacing" than the 42 with its swedge, than the 43 with its up-swept tip, or than the 47 with its heavy Tanto profile. That makes it a little more "politically correct." And, this profile, which actually resembles the AFCK's, is excellent for every-day tasks.

Notice the nice choile at the base of the blade. This makes sharpening the whole edge from tip to base, easier.

Like any Bali-Song, the 31 locks open tightly and becomes almost as strong as a fixed-blade knife. Lock failures, which have been reported on every other folding knife lock design, are unheard of on well-build balisongs such as the 31. So, you can lock your 31 open and know that you have a strong, reliable knife ready for your task.

And, you can lock it shut and carry it knowing that it's not going to drop open in your pocket and cut you.

Ready for your task is that the 31 is really about. With the shorter, more pocketable length, the clip, and the new blade profile, the 31 is a very practical balisong. This is the every-day-carry Bali-Song.

Of course, one of the reasons I like balisong knives is that they take something practical and utilitarian, a pocket knife, and make it creative, exotic and even fun by adding the potential for elaborate, creative manipulation techniques. So, a natural question is: how does the 31 flip?

Well, I've always found 3-inch balisongs to be just a bit small for my hands. Some years ago, though, I was introducing the balisong to several people including a rather petite lady. She was having a lot of troubles with the BM45 that I'd loaned her. Then, I noticed how massive that knife looked in her hand. I dug around in my bag and found a BM35 (the 3-inch Bali-Song that Benchmade previously offered). It was perfect. She took to it instantly.

My own manipulation style features a lot of what I call "inter-digital stuff," where the handles pass between my fingers. On 3-inch balisongs including the 31, I often find myself simply running out of handle before I run out of fingers. So, the shorter length does limit me just a bit. But, I've had a lot of fun manipulating the 31. Aerial techniques took a bit of an adjustment but came up to speed quickly. (Even if you're an aerial pro with a 4" balisong, I'd suggest taping the blade on your 31 just for little bit while you adjust to the smaller size.)

The BM31 features the same adjustable pivot joints as the 42/3/7. So, you can adjust the pivot joints just the way you like them. However, the pivot pins are not intended to be disassembled by the customer.

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Yes, the shorter length is big news. Yes, the new profile is a nice addition to the current Bali-Song line. Yes, the pocket clip is a great new feature.

But the real story on the BM31 is the handles. The handles on the 42, 43, and 47 are cast titanium. The handles on the 31 are titanium too, but they're made with a new process called "Metal Injection Molding," MIM.

When you think of injection Molding, you usually think of plastic. In plastic injection Molding, the molten plastic is injected under high pressure into a metal (usually steel but sometimes aluminum) mold. High pressure forces all the air out of the mold and assure that plastic fills the mold with no voids. High pressure assures that the plastic fills the mold quickly before the plastic begins to cool and harden. Once the plastic is in the mold, it cools and hardens assuming the shape dictated by the mold. Then, the mold is opened and the finished part is removed.

In theory, you could apply this process to metal? You could just inject molten metal into a mold under high pressure and it would harden to the shape dictated by the mold. But, what would you make the mold out of? Flowing molten steel is about 1500-2000F. If you inject a material that hot into a steel mold, the mold will be at least partially melted by the molten material. The mold has to be made of something with a melting point several times that of the material being molded. Of course, the rest of the injection molding machine also has to be made of a similar high-temperature material. To try to injection-mold steel you might try a mold and a machine made of ceramic. But, ceramic materials are very brittle and wouldn't withstand the pressure. In fact, there is no practical material suitable to make a mold and a machine to injection-mold metal.

So, how does "Metal Injection Molding" work? Well, it's different. The metal, still solid, is ground into a fine powder. That solid powder is mixed with another fine powder made of a "binder" material which is often a plastic or a form of wax. In a process very similar to plastic injection molding, this powder mixture is then injected into a mold made of steel or aluminum with mild heat and high pressure. The heat and pressure melt the binder material but not the metal. The binder material, and the still powdered metal with it, hardens as it cools in the mold. What comes out of the mold is a part in the correct shape that is made of still powdered metal held together in the desired shape by the binder material. That part is put into a furnace and carefully heated. If you do it just right, the binder material will evaporate (this is called "debinding") and the metal powder will "sinter" and become a solid mass. If you do it just right (part of the trick is to do it in a vacuum), that solid metal mass will keep the shape that it was molded into. Obviously, the part shrinks as it debinds and sinters. In fact, the part that comes out of the mold has to be as much as 33% larger than the finished part will be.

Here's an animated graphic from Sinter Metal Technologies website that illustrates the process.

The basic technology for MIM has been around since WWII. But, it's only in the last ten years or so that it's really become practical and started to achieve industrial use. MIM of titanium is especially new.

If you'd like to study MIM in a bit more depth, here are some websites to start with:

MIM is usually applied only to small parts. In fact, the BM31's handles are quite large by MIM standards. They're among the largest and most complex parts currently being produced out of titanium using MIM. In fact, Benchmade would like to make the handles for their larger model 42, 43 and 47 using MIM, but there simply is no MIM vendor who can handle such a large, complex part in titanium right now. Hopefully, as processed develops, that will change.

One might reasonably ask why Benchmade would pursue such an advanced technique for the BM31. Why not just stick with the casting process they've been using for the 42/3/7? The answer is that the MIM process creates parts that are solid with no casting voids. MIM parts also have better surface finish than cast parts so they need less post-Molding/casting finish work. Once you get the process down, MIM is quite cost-competitive with conventional casting.

The MIM process, though, did force Benchmade to slightly redesign the skeleton hole pattern. The outer shape of the large holes is actually oval-shaped and the counter-sinking is much more dramatic.

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Right now, though, a BM31 owner can brag that while its blade is very sharp, the real cutting edge in their knife is the handles.

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