Extrema Ratio HF2 In depth initial thoughts

Extrema Ratio HF2

The HF stands for "heavy Folder. This doesn't mean heavy as in weight but rather Heavy as in "heavy duty" folder. What qualifies this as "Heavy duty"? Well this liner locking blade can be completely locked open by inserting a thick steel pin into an offset hole (from the main pivot axis) in the tang and the T8082 alloy body of the knife, essentially stopping it from being closed accidentally. (unless the knife body is destroyed!)

Extrema Ratio HF2, a tactical advantage!

The Extrema Ratio HF2 has a dual role as I see it. Firstly, as a regular liner locking flipper folder, 

The Extrema Ratio HF2  is a large liner locking flipper folder

Not your bog standard liner locking folder, the Extrema Ratio HF2 D (the D stands for drop point, there is also a Tanto version and a Desert warfare coloration model too)

The Extrema ratio HF2 also features a chunky steel butt which could function as a weapon/persuader glass smasher

which can be deployed and operated quickly and efficiently (it's a flipper). 

Secondly, if one has to encounter more "vigorous tasks", then the folder can be locked open and effectively reinforced via the insertion of a steel pin 

Steel "safety" pin supplied on a small piece of shock cord and split ring (the latter I intend to change at some point to a thicker stainless ring). The pin (I didn't measure the diameter) is probably 1/4 (6.35mm) as 6.5mm is too wide for the scale hole and 6mm is too loose. I know the RAOII pin has a 1/4 inch 20 threaded hole.

which then prevents the blade from closing no matter what. 

I actually replaced (because I already had them and use them for a multitude of things, other than their intended end use-fishing) the split ring which came with this safety pin with a mega strong stainless steel split ring of similar durability to the pin itself.

Before......

After replacing (with a 100Kg breaking strength split ring) the rather flimsy looking split ring that came attached to the safety pin.

The end of the steel safety pin can be seen above the main pivot bolt.

The knife would need to be destroyed for the blade to close. if the knife is destroyed then so too, it follows the user's hand/s would also be destroyed from the ensuing forces!

So what is the purpose of the pin? Under "vigorous movement", ie ones hands with either gloves on or not may encounter the liner locking spring. This is always inevitable with a liner lock design 

The liner as seen from above (top side of the knife). There is a reassuring "click" heard and felt as the blade is locked open.

Precision ground mating surface provides an instant lock up with no movement experienced when the blade is forcibly rocked back and forwards

and as such one should never be too "aggressive" with hand movements  on a liner lock. If the pin is inserted, then even if the liner was to slip or be accidentally moved by ones hands, the blade can never close upon the user. It is a safety  redundancy mechanism and NOT  to suddenly turn the knife into a chopper. Besides that, Even if this was a fixed blade, one would not use it to chop with as it would just simply be too short and an incorrect blade geometry to be effective. 

The advantage here of the Extrema Ratio HF2 is in the cutting. It will have the same cutting effectiveness as a similar fixed blade knife. It's sturdy construction however will also allow it to undergo twisting motions that may otherwise damage a lesser folder's pivot mechanism.

How do I know this? By simply examining the mechanism. That's how. Under normal downward blade pressure all the force is still upon the blade stop pin. This pin is about 3mm in diameter and sandwiched between the alloy scales.

The optional safety pin, under normal operation does not encounter any loads. The load bearing parts are as normal, that is the blade stop pin (see image below) 

and the base of the tang and the end of the liner. Extrema Ratio are well-known for designing and manufacturing military products and as such the HF2 has redundancy built into it. If for example, the liner was to fail or even the stop pin to fail, then having the safety pin inserted would prevent the total collapse of the blade. In the case of the design of the HF2, there would be a slight amount of slop in the remaining mechanism but the knife would still be very useable in every sense. From a tactical standpoint this is of course a necessary thing in the military where a "Failsafe" is mandatory.

What about outside of any “military” end usage?

To quote Extrema Ratio

“..the well-known liner lock is enough safe.”

This means exactly what it says. Folding knives with few exceptions (for example: the RAOII, extensively tested by BCT) are capable of performing similar tasks as an equivalent sized fixed blades, without incurring any mechanical damage. The main use for a folding knife is to cut. A good design should be easy for the user to extract the blade, a more versatile design could involve simply one handed operation (in this case the Extrema Ratio HF2 is a “flipper”* ).

*A note here, one can’t have a flipper with a solid back, since the flipper (the guard) needs to rotate out past the back of the knife body. (see images).

Also see here: as a reference to a German forum where they also discuss the use of the insertion pin.



As reference to extreme use?

“...as much as a fixed blade...” in reference to using the safety pin.

“ ...a sturdy and reliable knife...”

What do these manufacturer’s statements mean?

Well, it is easier to say what it doesn’t mean, and it doesn’t mean by inserting the safety pin, turns the HF2 knife into a fixed blade, and hence all of the qualities of a fixed blade. No, it means that there is a measure of redundancy like stated above. As part of that redundancy, a simple mechanism like a LAWKs function (the red locking lever in this case- Extrema Ratio's take on a LAWKS system), prevents the closure of the blade when it is engaged. If you are not familiar with how this works, I will explain here:

By sliding a rotating steel plate (Red coloured plate) until the word “LOCK” appears on the body of the knife.

(it’s printed on the knife body), this plate internally prevents the liner from becoming flush with the inner scale and hence prevents the blade from closing. (see below) There is a distinct "click" felt and hear when this locking system is properly engaged and the word lock is exposed on the body of the knife.

Red locking device not engaged. Not excellent lock up position, ie the liner has not just engaged the edge of the tang but almost 1mm in from the edge.

Red locking device engaged. The liner can not be accidentally pushed against the scales, as there is now nowhere for it to move in order for the blade to be closed.

To insert the safety pin, the Red lock must NOT be engaged. Insert pin then engage the lock. Not only does this action retain the safety pin but it also of course engages the Red lock itself.

 

Note the red locking safety partially occluding the hole through the knife body

The pin, as I understand it, is really a form of “Tactical” redundancy.

The Extrema Ratio HF2 is a big folder but how big is big?

In terms of size when folded, the Extrema Ratio HF2 is still a good deal smaller (approximately less than ¾ the length) than say my Raidops Black Tiger MK2 in it’s scabbard, as a fair comparison.

A fair comparison between knives with similar shaped and size blades.

When extended, the Extrema Ratio HF2 is larger in size than say the Black Tiger MK2.

The blade here of the Extrema Ratio HF2 is slightly longer than the other small fixed bade knife.

How does the Extrema Ratio HF2 compare with "standard sized folders?

I would class this Nieto lock back folder (shown above) slightly larger than an average folding and locking knife.

How about a comparison blade thickness to a similar sized fixed blade?

Extrema Ratio HF2 lower image compared against my RAIDOPS Black Tiger MK2.

Carry system

In terms of carry the Extrema Ratio HF2 must be either carried within the pouch it came supplied with, or deep pocket carry. The Extrema ratio HF2 should not be thrown into a pack or bag as the blade being so big, can easily develop enough momentum to come out of the knife body with little movement. 

The knife comes with a carry pouch made from ballistic nylon.

Backside view of carry pouch showing Velcro belt loop

Front side view of Belt pouch for the Extrema Ratio HF2-Velcro flap closure. The ballistic Nylon pouch goes without saying, is very well stitched.

Maybe this can be reduced slightly if one tightens the pivot bolt, however, as it arrived from the factory, the pivoting mechanism for flipper action was absolutely fine for my usage.

 What do I mean by "more vigorous tasks"?

I do not mean the same sorts of tests you saw me doing with the Extrema Ratio RAOII (ie chopping through hardwood branches). That's because smashing the RAOII blade, either locked with the pin or not, results in a compressive force against the blade stop on this very sturdy and strong folder. There is nowhere for the blade to move as a compressive force is countered by the large blade stop itself (made from steel). Plus if the roller-type lock mechanism accidentally disengages, there is zero slop between the blade stop and the inserted safety pin. 

Now in the case of the HF2, the blade stop is not a flat plate of steel but a steel pin like as in most liner lock knives. Applying great force (via a levering action (it's a long blade) to the stop pin, will deliver a "bending" force to the stop pin. This pin, is held in place via machined holes in the T8082 alloy scales. 



Some background knowledge 



Any frame lock or liner lock designed knife can be subject to the following: P=F/A. If you have forgotten your physics, that's Pressure equals Force divided by Area. In this case, the Force (nothing to do with Luke Skywalker) comes from forces working in the same  plane as the blade) on the blade. The "Area" is the area of the mated surfaces comprising the spring liner, whether that be from a traditional liner locking knife to a fancy pants frame locking knife and the back of the blade tang. 
In terms of safety, the frame lock is the worst (I'll explain why in another blog).

If there is no LAWKS system present or the equivalent, such as seen in this Extrema Ratio model HF2, then accidental closure of the blade could occur under very vigorous hand movement, resulting in the accidental disengagement of the liner. However, if the knife is used as intended then this is highly unlikely to occur. Trust me the YT videos showing this or suggesting this are total BS, as forces are applied to the cutting edge under normal intended usage. Now you are saying, "but what about abnormal conditions?" I reply by saying, "yes, what about them? What abnormal conditions? The edge of the blade is used to cut, end of story, not the spine, not even in your wildest dreams (except on You Tube fanciful videos of course- The "spine whacking" videos I'm referring to).

Now quickly, any roller lock or Benchmade type roller lock or Ganzo type copy? whatever, roller lock can't resist large forces upon the locking mechanism springs which can arise under severe vibration or bashing the spine against immovable objects. The roller type lock is very strong though and to protect against any vibrational forces, Extrema Ratio give you the option of inserting a steel pin to prevent any blade closure on either of their RAO models (Heaviest folders). The traditional back locking design (and any modification of that such as Cold Steel's, triad lock and or the Extrema Ratio locking system seen in their Fulcrum folder) is a different story and one for a different blog.

All liner locks will be damaged with this ridiculous spine smashing action seen on numerous video's, mostly by "would be if I could be s," (WBIICB) because that's the only conclusion I can come to about the persona of such people conducting these sorts of tests on any folder. One person started it on YT and now many follow like sheep LOL! This sort of test proves nothing whatsoever, except to highlight a WBIICB.

A backwards smashing action will cause a liner to undergo initially compressive forces and then possible slippage due to vibration and subsequent loss of frictional forces, overcoming friction at the tang and liner lock. If the force is constant then the liner could fail. However, as pointed out above, this is a totally unrealistic scenario.

Now back to the real world
A lock on a folder is to prevent accidental closure, end of story. A lock is not to prevent the blade from closing when the spine is smashed against an unyielding object. What is important is that the blade does not collapse when pressure is applied to the edge, during cutting, or the blade does not collapse during thrusting, or the blade does not collapse during rapid movements exerting forces in all directions; or the blade does not collapse from the action of one's hands upon the locking mechanism (in this case it can't due to the RED locking system, eg like a sort of LAWKS type lock- or if the pin is used. 
So as long as the construction of the knife is such that the tang stop, is exactly that, a structure which physically prevents the blade from moving in an UPWARDS direction-not downwards, then all will be fine. 

The Extrema Ratio HF2 is part of the "Heavy Folder" model line as stated above.
Now a liner lock design has a stop pin (see image). It is this stop pin 

that prevents the blade from collapsing when a downward force is applied to the edge during cutting. For a given force applied to that edge, will increase the force upon the stop pin as the blade length increases. This is simple physics and this example can be thought of as the blade acting as a lever, rotating about the main pivot point. As the length of a blade increases, this would be equivalent to increasing the length of a lever in order to achieve a greater force when for example lifting something.

One may ask, why  use a liner lock, instead of a back lock or something else? The liner lock does not need to be that heavy (remember we are talking about a larger knife) and liner locks by their nature do not easily retain dirt and debris which could interfere with their function. Unlike a back locking mechanism, which due to the notch in the spine, if this retains debris, it will not lock properly. Or due to the tight tolerances of a back lock construction, they need to be kept very clean in order to allow the pivoting of the lock bar. If speed is of the essence, then this could cause a problem. The knife back on a liner lock is therefore generally "open" 

Since the back of a liner lock is essentially an open design, there is less chance for debris to hinder the knife opening mechanism. The heavily grooved scale separator is made from steel. Notice this large ribbed steel insert. This form of knife construction makes for a very strong and rigid folder. Why? because instead of using regular standoffs (most manufacturer's use 2, (one at the butt end and one part way along the scales) some use 3 (one at the butt end and two along the spine- this is better), however, the use of a large steel insert gives maximum surface area for maximum strength and rigidity of the scales.

and this is one reason why debris is less likely to be caught within this type of folder. eg compare with traditional slip joints and back lock knife construction. Now the addition of this large "safety" pin on the Extrema Ratio HF2 is to allow a much greater safety margin during downward pressure on the blade. It is not there in order to use this type of folder to chop objects. Extrema Ratio do not say this HF2 can be used to chop things. Certainly, the RAOII can be successfully used either locked with the safety pin or unlocked (Although I would advice to use the safety pin) to chop thick branches with ease.


Materials of choice
Matensitic cobalt stainless tool steel, N690 for blade steel at HRC 58 and a hand ground deadly sharp convex edge. Tanto or drop point versions available, T6082 high strength Aluminium alloy scales, stainless hardware, removable pocket clip 

left of right hand side pocket clips included as well as Allen driver for changing or removing the clip.

and for either left or right handed carry in this fashion. I hate pocket clips personally, it's a dead give away you are carrying and there is never a guarantee one can rapidly deploy that knife for whatever reason when using a pocket clip. The time you want it will be the time it gets snagged upon your clothing somehow.

There are basically 2 flavours of colour schemes for these models; the desert camo and the classic black. In this case, the black is a completely anti-reflective coating on both blade and scales, along with all other parts (with exception of my slight modification of the split ring which would not be suitable for a military application- glinting in the sunlight!).

Without a doubt, the anti-reflective black is the least noticeable to the human eye color scheme. From a "covert carry" POV this is the only choice IMHO.
it goes without saying that the Extrema Ratio HF2 came to me deadly razor sharp out of the box. In fact I managed to cut myself "commando style", NOT!, with it only days after playing around with it; and that was literally just touching the blade.



The mechanism in summary


Regular liner lock

Safety liner lock stop (red lever)

Safety pin (redundancy feature), came on shock cord

Pocket clip/s reversible.

Fully fine adjustable main pivot, as seen in fine cutlery and cutting instruments such as pruning secateurs!

The main pivot bolt can be fine adjusted by first removing the small grub screw. I recommend using Loctite 242 when replacing these screws

Maintenance

Other than basic cleaning, the main pivot can be fine adjusted by firstly removing the small straight slotted screw next to the main pivot bolt head (see above) and then either tightening or loosening the main pivot bolt. Once this is done, I would recommend a small amount of Loctite 242 be used for reassembly. The Loctite can help prevent accidental loosening due to vibrations.

The overall construction

Torx head bolts

The pivot bolt is a different metal (low magnetic attraction) from the bolt head (strongly magnetic)

Anodising for corrosion resistance
The back spacer is made from steel and not aluminium

Scale milling pattern for added secure grip.

Italian Knife, Italian boots!

Extrema Ratio's specifications can be found here:


Stay tuned for a field review of the Extrema Ratio HF2 coming up soon on:

Breaking News!!!! Here is Part ONE of my review on the Extrema Ratio HF2D, check it out!

BushCampingTools


PS also see this review of the Extrema Ratio HF1T

https://hardcorecampingtools.blogspot.com/2020/12/extrema-ratio-hf1t-heavy-duty-folder.html