Rat Worx MRX Chain Drive Auto Knife

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Apr 22, 2013
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16
Though Rat Worx might be new to the knife market, they've been designing and manufacturing gun parts and accessories, aerospace bearings, custom surgical tools, and even robotic hands for a long time. In fact, they spent three years testing the MRX before finalizing on a design for production, and it shows.

Many look at the unique chain drive as a gimmick or potential reliability problem, but I show how the design works and why it makes perfect sense for a knife designed to be the world's strongest auto knife.

[video=youtube;n4UkvCfWVak]http://www.youtube.com/watch?v=n4UkvCfWVak[/video]
 
Thank you for taking the knife apart to show us this:

MRX+auto+internal+edit.jpg


The red circles indicate the only metal keeping the blade from flying out of the handle, metal that functions as a focal point for lateral (side) loading of the blade, metal that shares the vertical strain of use (stretching) as the tang cut-out rests against the stop-pin. Did you mention whether the handles were steel or aluminum?

What concerns me: This is obviously meant to be a knife that can handle a LOT of stress, but its design is inherently weaker than most I have ever seen! Every lateral & vertical load or impact threatens to break the blade from the thin tang-arms that hold it to the handle, not to mention the stop pin resting in aluminum rather than steel, making it lighter but also more easily deformed against the stresses described above.

Perhaps these concerns are unfounded in practice, but theoretically this may be among the worst designs I've come across in terms of strength. A knife is only as strong as its weakest point. The rest is just 'gimmickry' - very neat, but meaningless if the blade snaps off from the handle.
 
Quite expensive for something that has 2 very obvious weak points, on the plus side they do offer a lifetime warranty.

***Update***1/28/14

Several videos on page 2 are linked to Ratworx facebook, It would seem my earlier stated opinion is just an uneducated assumption having never handled this knife.

Thank You to the OP for leading some of us Nay-sayers to the light.
 
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The Southard isn't quite as bad:

Southard_Breakdown.jpg


Similar to the Bodega:

7a210a8678bc11e39b761240926e6356_8.jpg


But this one is just terrible...

I don't understand these internal stop-pin designs. They are more complicated than external stop-pins and can present substantial decrease in strength compared to the SAME design without that milling in the tang. Or why not just put the pin through the tang and mill steel liners on either side? That is more complicated than thumb-stud stop-pins but offers similar strength without the visibility of the stop-pin (see the Kershaw EnerG). Putting a hole in the blade or tang reduces strength and presents a focal point for stress. Unless you've engineered the rest of the blade to compensate for that loss of strength... Why are people doing this? Because laser-cutting and CNC make it possible? Just because you can do it doesn't mean it makes sense... *shrug*
 
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Thank you for taking the knife apart to show us this:

MRX+auto+internal+edit.jpg


The red circles indicate the only metal keeping the blade from flying out of the handle, metal that functions as a focal point for lateral (side) loading of the blade, metal that shares the vertical strain of use (stretching) as the tang cut-out rests against the stop-pin. Did you mention whether the handles were steel or aluminum?

What concerns me: This is obviously meant to be a knife that can handle a LOT of stress, but its design is inherently weaker than most I have ever seen! Every lateral & vertical load or impact threatens to break the blade from the thin tang-arms that hold it to the handle, not to mention the stop pin resting in aluminum rather than steel, making it lighter but also more easily deformed against the stresses described above.

Perhaps these concerns are unfounded in practice, but theoretically this may be among the worst designs I've come across in terms of strength. A knife is only as strong as its weakest point. The rest is just 'gimmickry' - very neat, but meaningless if the blade snaps off from the handle.

Your circles are quite misleading, and I hope this just an oversight and not intentional. They and the wording of your post seem to indicate that the metal in those areas is limited to that which is brushed, ignoring the metal that is finished in black Guncote. Ironically, your lower circle does not even indicate the narrowest place on the spine, which is at the very bottom of the stop pin slot.

Here are better photos of those two areas, the smaller of which mics at 0.120" wide by 0.150" thick:





Additionally, the stop pin only bears stress until the button is released. The steel button then wedges into the gap between the fourth and fifth teeth, providing 100% of the lockup against opening and closing forces.

These areas are likely the weakest points of the knife, but they aren't as wafer thin as you are suggesting, and they have not proven to be a failure point for any of the knives used in testing over the course of three years.
 
Your circles are quite misleading, and I hope this just an oversight and not intentional. They and the wording of your post seem to indicate that the metal in those areas is limited to that which is brushed, ignoring the metal that is finished in black Guncote. Ironically, your lower circle does not even indicate the narrowest place on the spine, which is at the very bottom of the stop pin slot.

Here are better photos of those two areas, the smaller of which mics at 0.120" wide by 0.150" thick:





Additionally, the stop pin only bears stress until the button is released. The steel button then wedges into the gap between the fourth and fifth teeth, providing 100% of the lockup against opening and closing forces.

These areas are likely the weakest points of the knife, but they aren't as wafer thin as you are suggesting, and they have not proven to be a failure point for any of the knives used in testing over the course of three years.

No intentional oversight, I am glad to see there is a tiny bit more metal than the brushed area, and thank you for the close-up shots, though I still do not see any irony or where i missed anything... did you mean on the belly where it meets the stop-pin? I could have circled that spot as well but as it is housed within the handle it is less likely to become a fulcrum-point for side-loads against the blade than the spot I indicated under the choil.

Thank you especially for the measurements that indicate just how much metal supports the structural integrity of this blade, namely two arms ~1/8 x 1/8". That is the entire strength of the blade... basically two prongs on a fork. How difficult is it to cause a fracture there? Please demonstrate the strength of "the world's strongest auto knife". I am glad to hear that you haven't experienced failure in your testing and even noted that my concerns may be "unfounded in practice", but this design remains inherently weaker than almost every other design out there as a simple matter of material strength.

Now if you really think that the other thin spot in the tang is weaker than what I've indicated, that isn't exactly good news, but it is again a simple matter to test and demonstrate.

Regarding the lock-button bearing stress rather than the stop-pin, that wasn't even my criticism - the handle is aluminum, isn't it? With no steel liners? Heavy use will deform the aluminum faster than it would deform steel, another inherent weakness but an asset in reducing weight. The lock-button functioning as stop-pin is great, though it must share the stress with the internal stop-pin, yes? That would be a good thing if the tang-track was so machined. But again, the little tang-arms supporting the blade share the stress of use as well (as does the pivot).


Another thing i do not understand about this design - if you don't need the stop-pin to lock the blade open and endure stress, why even have one??? The lock-button can act as both stop-pin and blade-lock and blade-stop when the knife is closed, you don't need that internal stop-pin and routed tang at all... ?

My apologies if you have taken offense, but the flaws in this design are too glaringly obvious for it to go un-commented upon, especially with the claim of "strongest" in your first post. I have no axe to grind and intend no personal offense. I also do not see why you cannot easily improve the design and keep the chain-drive gimmick to sell it as unique. (I avoided mentioning the risk of debris and corrosion impairing chain flexibility because I assumed that issue had already been addressed prior to production... then again, perhaps it has not been)
 
I picked up a MRX as soon as they were released. I have used it as my EDC for around 6 months. Usually the first comment guys make when they see it is that the knife is pretty cool, original, and they are always impressed how hard it snaps open. That is usually followed by a question about what effect pocket lint has on the chain. I like to reply it has the same effect on the chain of my MRX that it does on the chain on my Shovelhead. Zero. I Valentina cleaned it after 6 months of use. Then the question of reliability comes up. I ask the guy questioning the reliability of the mechanism how many times he figures a production MRX has been fired in documented testing until it failed. The responses are 10,000 or 20,000. I then point out that one of the MRX prototypes was fired 420,000 before failure occurred. The failure was not in the mechanism, but the button lost just enough to not hold the blade shut.
I am lucky to call the designer of this knife one of my friends. I can pretty much guarantee he will see this post, and the concerns that have been raised about the strength of the design, and get to work on some brutal "Research And Testing". This will more than likely involve some sort of brutal torture test videos that will be publicly available.
 
You're confusing me with the designer. I have no relationship with the manufacturer other than discussing the design with him for this review, though I do realize that only he is capable of defending his design further.
 
Thank you for this great video. I do not see the metal breaking any time soon, at least not from opening and closing the knive. I believe the metal is thick enough for the tasks a folder is supposed to do. The Southard picture looks scary, but it seems there was a production flaw in that knive. Anyway the video is great and I am looking forward to the smaller version and the OTF.
 
I don't understand the criticism of the knife and why the red circles? How is that the weakest point of the knife? I'm no engineer but the areas don't look like stress areas to me when the knife is closed or opened. And it looks to me like they are machined into the steel that is gun coated too. The knives are expensive but I am finding out more and more you get what you pay for. I agree with the shovelhead comment too. My primary chain doesn't seem much affected by much of anything as long as the tension is correct. And then it effects shifting more than anything else. Beats me folks but opening and closing a knife close to a half million times before failure is pretty good in my book. keepem sharp
 
If a knife fails from simply opening and closing, there is a problem. Spring-failure is the usual cause of this as that is the ONLY place where the tool is being stressed. This design uses very long springs to try and reduce the wear, makes sense ... IF that is the only thing you use the tool for, opening and closing.

But a knife's primary purpose is cutting. This knife is quite thick, reducing cutting performance substantially, but that thickness is obviously there for a reason, namely strength and toughness - both vertical AND lateral. The length and thickness of the blade demand increased force from the user, and all of that force will end up concentrated at the juncture between blade and handle, where the support metal is reduced to two meager prongs of hardened steel, each ~1/8" x 1/8". On top of this is the lack of material strength supporting the lock-button/stop-pin, etc. since the scales appear to be linerless aluminum, prone to plastic deformation with hard or extended use.

A tool is only as strong as its weakest link.

If this is simply a Yo-Yo, meant to be opened and closed but nothing more, then indeed it will last quite long because of the springs.:thumbup:

But if it is meant to be used as a knife, it appears to have all the strength of an Opinel without the impressive cutting geometry. Repeated impacts (e.g. batoning, chopping, a spine-whack) may soon result in deformation of the aluminum around the lock-button if not failure of those little steel arms and loss of the blade :eek: Lateral stress (i.e. prying) will bend a thinner blade, maybe result in a broken tip, but that won't happen here because the blade is so thick... instead, the blade is likely to snap right out of the handle at those little arms.

The design is like a badly made rat-tail tang on a fixed blade - insufficient support for all but the most meager tasks for which a thinner, lighter knife which be much more appropriate. So what is the point of this design? Either it is a mistake or the knife is simply intended as an expensive display/conversation piece or a Yo-Yo. In either case, it is hardly "designed to be the world's strongest auto knife."

And again, I intend no offense to anyone in this, and I would LOVE a video demonstration of just how much stress this knife can handle, but from the images alone I'd have more confidence in the strength of a Buck 110 (to use a random example).

If the tang-track milled for the internal stop-pin where eliminated from the design, and steel support placed around the pivot and lock-button, THEN the design might compete for strength with other knives of similar size. It's great that their springs take so long to wear out.
 
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Do you have links to video or photos of people using auto knives for batoning and chopping? My google-fu comes up dry.
 
I am not knowledgeable enough to debate the strength of the design, but I will say it is interesting and the review was very well done. Thanks for sharing.
 
Do you have links to video or photos of people using auto knives for batoning and chopping? My google-fu comes up dry.

Thanks for the chuckle. :thumbup:

Google "microtech field test", and there is also a destruction test on a genuine microtech out there, trying to re-find it, that shows how much stress the blade and lock can take with repeated hammering (surprising).

Google "hogue hard use" and also "benchmade test". Benchmade puts out there own videos and there are numerous others demonstrating hard (ab)use of many models including the presidio, adamas, bedlam, infidel, etc. Also keep in mind that for quite a few Benchmade NON-auto models, as well as the Hogue, there is also an Axis-auto model wherein the only structural difference (at least in the case of Benchmade) is an additional tongue of metal on the tang that catches the lock-bar and moves the blade to where the coil-spring initiates automatic activation. Whatever stress the manual can take, so can the auto. The week-point on these knives is simply the springs.

You can also look for hard use videos of the Gerber Propel and DMF where again the manual and auto are structurally the same beyond the spring initiation.

If you fail to find these videos, I will make an effort to link/embed them ALL once I get a chance. There are quite a few competitors for "world's strongest auto".
 
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