Spyderco Air - a look at the weight in a different light

[Cliff Stamp]

I was doing some work with the AK-47 from Cold Steel while carrying the Air and curious to note just how much lighter the Air was if you normalized out the size because the AK-47 isn't overly heavy for its size.


Cold Steel AK-47 : 0.6 oz/in linear density
Spyderco Air : 0.22 oz/in linear density
ZT 0561 : 0.75 oz/in linear density
ER Fulcrum : 0.84 oz/in linear density

These were done on a very basic scale so they are +/- 0.02 at best.

It does show though in a dramatic fashion just how much lighter built the Air is compared to say the ZT 0561 which is considered a light knife "for its size" .

If the Air doesn't impress you then consider that the Havalon Piranta Edge is a plastic handled knife with a scalpel blade and it :

Havalon : 0.26 oz/in linear density

Is not even lighter than the Air per size.


There are other ways to look at it of course :

-linear as a function of edge length
-volume density (hard to interpret a meaning though)

[bpeezer]

do you also have weight/thickness numbers?

[Phantazm]

"length overall 5.96" (1.51 mm)
blade length 2.55" (65 mm)
blade steel CPM M4
length closed 3.41" (87 mm)
cutting edge 2.37" (60 mm)
weight 1.3 oz (37 g)
blade thickness 0.089" (2.3 mm)
handle material Titanium / Glass Fiber Laminate"

From spyderco themselves.

[Cliff Stamp]

No, but that is pretty trivial, blade or handle?

[vtvman]

The Air is approximately 0.393" according to this thread

http://www.spyderco.com/forums/showthre ... rco-handle

Can you confirm that Cliff?

[jabba359]

Interesting way to look at it, but size is determined by 3 spacial dimensions, not just length, so I'm not sure what exactly this particular exercise demonstrates. Does normalizing out the size mean you just extend the linear measurement while maintaining the same thickness and height? It seems that to maintain a knife with similar function and ergonomics while maintaining structural integrity, you'd likely have to increase the height and -to a lesser degree- thickness as well (obviously not on a 1:1 ratio to the linear scaling). This would obviously increase the weight more than just stretching it in one direction.

I'm also confused by you saying there is difficulty in interpreting meaning of volume density. Is it really too much harder than interpreting meaning of linear density? :confused: It seems to me that linear density only takes into account 1 dimension (length) while volume density would merely be one of two scenarios: #1. measuring the 3 outer dimensions (length, width, height) and calculating the total volume of space within those three dimensions (which will obviously include the "empty space" also contained within those borders) or #2. measuring actual volume displacement (easily accomplished by submerging in liquid).

Perhaps I'm just not correctly understanding what you are saying. :o It is a bit late at night here. But whatever it is you're trying to say, I can certainly agree with your assertation: the Air is one light knife! :D

[nirvanero]

Interesting way to look at it, but size is determined by 3 spacial dimensions, not just length, so I'm not sure what exactly this particular exercise demonstrates. Does normalizing out the size mean you just extend the linear measurement while maintaining the same thickness and height? It seems that to maintain a knife with similar function and ergonomics while maintaining structural integrity, you'd likely have to increase the height and -to a lesser degree- thickness as well (obviously not on a 1:1 ratio to the linear scaling). This would obviously increase the weight more than just stretching it in one direction.

I agree, comparing different knives with different shapes and sizes can lead to wrong conclusions except if we only look at it from a 2D perspective. A CF Military may have a higher linear density than the Air but both are feather-weights in their own class.

The truth is when you hold the Bradley design in your hand it's shocking how light it is, a 50% less weight than a CF Walker! Cliff, I guess you've tested this knife hard enough: what do you think about that very thin titanium liner lock?

[Cliff Stamp]

The Air is approximately 0.393" ...

This is is from 0.396 to 0.397"

Interesting way to look at it, but size is determined by 3 spacial dimensions, not just length, so I'm not sure what exactly this particular exercise demonstrates.

I was looking for a way to determine how light a knife was built essentially. It is trivially obvious that you just can not just go by raw weight because smaller knives can be seriously over built.

I'm also confused by you saying there is difficulty in interpreting meaning of volume density.

The densities are the same in all steels (to within significance) and similar with most handle materials. Plus for example a heavily skeletonized tang has the same density as a full slab tang but yet would it make sense to say it has the same weight per size?

The reason that they are lighter of built is that they lower the linear density. A knife of the same size is lighter in weight. There are some other useful ways to approach it of course, it is rare that any one statistic would give the full picture of performance.

(weight as a function of blade thickness for example, or edge length, or cutting/chopping ability, ...)

I agree, comparing different knives with different shapes and sizes can lead to wrong conclusions except if we only look at it from a 2D perspective.

It would depend on what conclusion you would form.

I would use it as a first order approximation to weight as a function of scope of work .

... what do you think about that very thin titanium liner lock?

In general I tend to not prefer liners or integrals for serious using knives for issues of :

-security
-wear
-impacts

But it generally is only restrictive on larger blades where forces get higher. However this Air has been modified :

-almost full grind (there is a very small transition bevel)
-<10 dps apex

The forces on it in general are so very low that I don't think the lock is an issue and thus an axis, tri-ad, or compression would not be of significant value because the blade itself is the weak point in any over loading.

I still don't get the double opening, but some people like it.

[Blerv]

There are other preferences too which are difficult to quantify. While I do not own an Air, the most appealing factors are the wharncliffe blade with a relatively thin grind and the CPM-M4.

I can't prove why those factors are more important to me but relative to my interests they strike the right cords. With a factory clip it would be a certain buy.

[dbcad]

Thank You Cliff, I always appreciate your take on things scientific. The Air has a very low linear density and fit's the name well :D

[nirvanero]

However this Air has been modified :

-almost full grind (there is a very small transition bevel)
-<10 dps apex

The forces on it in general are so very low that I don't think the lock is an issue and thus an axis, tri-ad, or compression would not be of significant value because the blade itself is the weak point in any over loading.

I still don't get the double opening, but some people like it.

That's a crazy grind but I guess on the limits of CPM-M4 heat-treated at Spyderco standards.

By the way, not even the designer seems to prefer his own opening, but in the other hand it makes the Air even lighter...

[greenewk]

I really need to get my paws on one of these... Absolutely love the design -- seems a near perfect gent's folder.

[Cliff Stamp]

There are other preferences too which are difficult to quantify.

There is no need to know why something appeals to you except when you want to find something else which has the same effect and try to eliminate guess/check extended purchases. But a lot of people like that as well and the frequency collection turn overs.

- seems a near perfect gent's folder.

Yeah, I carry it almost always in my watch pocket. Very nice and friendly knife to use even around people who can be uncomfortable with knives like the Delica/Endura.

That's a crazy grind but I guess on the limits of CPM-M4 heat-treated at Spyderco standards.

This is really nicely done, so much I am curious if it was a fluke as the performance is so well actually. The steel is so hard to grind that it actually ignores waterstones that can grind my Phil Wilson's 10V blade for example and that isn't a trivial thing to achieve.

It works perfectly fine with the grind I have on it. I would like to remove the very small transition bevel but the grindability makes it nontrivial for manual sharpening and you need more precision/patience than I have to do it with power tools.

Ideally I would like to see it with a nice full hollow and I might bug someone to do that in the near future. Still though small refinement to the already very nice cutting performance, especially that very high penetrating tip.

The Air has a very low linear density and fit's the name well :D

Yup, now just wait to collect the royalty checks coming in when it starts being adopted as a popular statistic.

[dbcad]

Could you give us a pic of your Air Cliff?? It would be neat to see what that kind of edge looks like :)

[Cliff Stamp]

This is the knife :



The very sharp edge bevel is approximately 7 dps, the primary grind is only 4 dps. This means to remove it I need to grind right between them at 5.5 dps, this requires an angle control free hand of less than a degree, good luck. The other issue is that this steel ignores most stones trivially so there is little feedback as there is a lot of skating so it is hard to tell if you are on that shoulder or one of the other bevels.



To be frank though it isn't like a 7 dps bevel is overly coarse / heavy for cutting, it just isn't necessary. I keep playing with it Murrary Carter style but it is slow going. You also have to use fine abrasives as if you try coarse and you slip and hit the edge you will blow out huge pieces, it really needs jig work to be sensibly removed.

The dark blade of course was from an acid wash from the previous owner (don't do that!) and you can see how that has faded from direct grinding on the primary compared to the choil area which is still very dark.

Really nice knife. I bought that mainly on a lark but it quickly became primary carry and I can't see it being removed for quite some time.

[bpeezer]

No, but that is pretty trivial, blade or handle?

I was thinking handle, I'm trying to find a balance I like for weight/handle thickness. For reference, the SS delica is too heavy for how thin it is, but the FRN delica is too light for how thick it is. May be a preposterous ratio to some, but it gives me a pretty good sense of how my hand will like a knife without taking geometric ergonomics into account.

[GoodEyeSniper]

By the way, not even the designer seems to prefer his own opening, but in the other hand it makes the Air even lighter...

I don't know why everyone seemed to misunderstand Gayle bradley from that video so badly. I thought he laid it out in plain english well enough. He clearly said the one hole is for opening, the other is for closing, and that is how it was designed and how he uses it...

[nirvanero]

I don't know why everyone seemed to misunderstand Gayle bradley from that video so badly. I thought he laid it out in plain english well enough. He clearly said the one hole is for opening, the other is for closing, and that is how it was designed and how he uses it...

First of all it's pretty obvious that Brayle's "opening" (or hole, name it as you wish) is used for closing the blade. I don't know if "everybody seemed to misunderstand GB" but the truth is english or plain english is not my mother language and I just undestood from the video that it was left there as part of the original design and as everybody else "the only time" he uses it is when more grip is needed, but "anybody uses it". It makes perfect sense to me that Mr Bradley also uses the more comfortable "opening" for closing, maybe I'm wrong.

[gunmike1]

That's a crazy grind but I guess on the limits of CPM-M4 heat-treated at Spyderco standards.

This is really nicely done, so much I am curious if it was a fluke as the performance is so well actually. The steel is so hard to grind that it actually ignores waterstones that can grind my Phil Wilson's 10V blade for example and that isn't a trivial thing to achieve.

It works perfectly fine with the grind I have on it. I would like to remove the very small transition bevel but the grindability makes it nontrivial for manual sharpening and you need more precision/patience than I have to do it with power tools.

Ideally I would like to see it with a nice full hollow and I might bug someone to do that in the near future. Still though small refinement to the already very nice cutting performance, especially that very high penetrating tip.

Now that I got my Air delivered to me, and see the need to vastly thin out the blade (mine is .017" behind the edge bevel), I am going to send it in for a regrind to make it about .005" behind the bevel. I searched and found this very informative thread. I was wondering if you ever did a zero grind, or got the high hollow grind you mentioned wanting done on your Air. I'm curious how the edge on the M4 in the Air holds up at 4 dps with a 15 dps microbevel for light cutting. On SGPS and ZDP I found they could get a little more chippy than I like if the microbevel wasn't visible to the naked eye when doing my light duty cutting. Since at that point it isn't really a microbevel, meaning it's more prone to burring during sharpening, I settled into about 7 dps with a 15 dps true microbevel on my ZDP Caly Jr with a Krein high hollow grind (.005" behind the bevel) and find the edge doesn't have any more than very tiny chips that are quickly removed during sharpening. On the SGPS on the Fallkniven you gave me to test with the same geometry, I found out that chips into the primary grind could easily happen with bad technique like twisting during a deep cut. Staples easily can do similar damage. So I love the cutting ability of the super thin high hollow grinds with flat to the stone bevels, but also have a bit of trepidation of damage into the primary. While I haven't experienced that on my Caly Jr, and don't expect it on the Air without bad technique or hitting a staple, in the back of my mind I'm wondering if I should play it more safe and keep a full flat grind on my more expensive Air. If the M4 in the Air can avoid excessive chipping at a flat to the stone angle with a tiny microbevel in light cutting, then I'd say it's worth the small risk of a bad chip into the primary for the much easier flat to the stone sharpening and increased cutting ability of a high hollow grind. But if I need to go with a 7 dps angle to have the edge hold together anyway, do you think going with a full flat grind to a .005" thickness behind the edge would considerably penalize the sharpening and cutting ability? Obviously over time the edge would just continue to thicken on the flat grind, but it would certainly lower the risk of a chip getting into the primary. Considering I have been using my high hollow grind ZDP Caly Jr for so long without problems I should probably just risk it and go with the high hollow grind on my Air, since M4 should be able easily handle thinner angles than ZDP 189.