Kydex-Kevlar Sheath

Andrew Lynch

Andrew Lynch

Joined
Feb 6, 2000
Messages
3,021
Carl Thiele (aka cj_7 and survivor) and I have been collaborating recently on a sheath project (for a BM-E). It is a sheath designed for ultimate durability, especially in extremely cold temperatures. Now that I think about it, this sheath is designed for Cliff Stamp. Given its nuclear characteristics, I thought you guys might be interested ;)

It consists of an inner layer of 0.090" kydex, a central layer of kevlar, and an outer layer of 0.090" kydex. The belt-attachment system, which is a revolution in strength, is Carl's design. Basically, the outer kydex layer holds the chicago screw posts. Also, everything on this sheath is ambi.

Here are a few pics that Carl took of it:

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If the molding doesn't look as crisp as you expected, that is because of the sheer thickness of the material being molded.

There is a piece of harness leather around the sheath where the chicago screws for belt attachment are. That is just for support while the belt attachment is not in place.

Hopefully Carl will be around in a while to give his input and comments. He has already done some rather extreme testing of the sheath and it has come through well, so far. He recently posted this on another forum:

"For what this is worth...
Supporting either end of an empty kydex/kevlar sheath on steel 4X4 beams, it supported 250 lbs with about 1/2 inch of sag only while the weight was applied, after which it returned straight. The test was conducted after leaving the sheath in the freezer over night (0 degrees F). Both sides were tested with the same result.

The same sheath was dropped from a height of 25 feet onto concrete, knife inserted (BM/E) point down same temperature as above. Close inspection revealed no damage.

Further testing will continue and I will report results.
-carl"
This is a prototype and Carl and I are already tweaking the design. Comments and suggestions are welcome :D
 
Guys! I particularly like your design for the "drain"!

Have you considered the use of .06 Kydex for the "sandwich"? It would significantly reduce the weight of the sheath for such a large knife, and reduce your "front end."

Question: How many layers of Kevlar are you using and at what weight?
 
Thanks Brian!

I opted with 0.090" mainly for durability reasons. Also, 0.090" kydex anchors the load-bearing chicago screws much better than 0.060".

We're using one layer of kevlar. I don't remember the specs (Carl's got all that info). I'll tell you one thing, that stuff is HELL to cut.

I think you'll find the belt attachment system interesting!
 
Andrew,

Good Work!

I'll think about any design tweaks, and let you know. Let me know when you have refined it and are ready to take orders.

Cheers,

--Mike
 
Thanks Mike :)

I'll let you know. Man, I've got to get some sleep. Day light savings time just made it 3 AM :grumpy:
 
Whoa baby!! That sheath is fit for a Busse.

Great work guys! How about doing a sheath pass around?? ;) ;)
 
That's a nuclear sheath, well worthy of carrying a Busse beast!!! Very nice work you two. Way to "think outside the kydex" to come up with better pants for our Busses.
 
Specs on the kevlar are:
Weight: 3.6 oz per sq.yd,
Denier: 400,
Width: 63" Inches,
Thickness: 7.0(mils) 0.18(mm),
Weave: Plain,
Breaking Strength: Warp & Weft
Warp: 530(lbf/in)
Weft: 530(lbf/in).

As Kevlar will not stretch and/or mold, the process had to be to create an entire sheath, add and glue the kevlar, and add, glue and mold the final layer.

I can say that I am rapidly becoming a convert to "plastic" sheaths given what I've already seen this one survive. Until now, I'd been convinced that only certain carefully chosen leathers, stitching and rivets could be employed for durable sheaths. There will be more on this when our testing reaches some maturity. Everything so far is quite preliminary. We are encouraged by what we have seem so far (the drop test at O degrees F and the empty suspended sheath supporting 250 pounds- also at 0 degrees F). Both of these tests resulted in total conventional kydex sheath failure.
-carl
 
WOW!!! Very cool!:cool: I had the chance to see some of Andrew's kydex work up close and it is AWESOME!!!!


This nuclear kydex rig rocks!!!!

Jerry
 
Originally posted by Andrew Lynch
I'll tell you one thing, that stuff is HELL to cut.
Click to expand...

That is why I won't be chasing you guys on this one. I like my tools too much.

Just out of curiosity, have you guys tested just the double layer of .09 sans Kevlar? You have almost 3/16" of LAMINATED Kydex on that bad boy.
 
Brian-
Almost a year ago when this subject moved sharply into focus, an associate made a kydex sheath of two layers- no fiber (like kevlar) of any kind. The layers were glued together to form a true laminate. He sent me the sheath and I executed one test before sending it back to him in pieces: removing the BM/E, I placed each end of the sheath on a volume of encyclopedia and stood on the sheath. I weigh about 240 in sock feet. I thought this a good test at room temperature because one never knows when they might step on their sheath (:footinmou don't go there :D ). It snapped immediately- in half.

That sheath might have been 0.060 kydex- neither of us remember for sure. But remember we are talking room temperature, or about 60 degrees. Andrews sheath took the same test in stride and also took a more formal version (exactly 250 lbs on a barbell, sheath supported on steel) at zero degrees F. It creaked (and sounded like it cracked) but inspection revealed no cracks. We then "refroze" the sheath and tried the other side in exactly the same way. More creakes, but no cracke or failure.

I think a key element of these tests is the glue as well as the fibre. I am convinced the fibre contributed significantly, but could not have done so without being bonded to the inner and outer sheath. I think the creaking came from the chicago screws (CC's) which we discovered had come loose during the freezing (about 1/2 turn). The test was repeated but the screws were tightened BEFORE the test and after freezing and whole test became noisless.

Final point: While a role of the kevlar is strength, another important role is sheath integrity. That is, should it crack through, we want it to remain a serviceable sheath (not fall apart). The primary role of any sheath is to prevent the blade from contact with friendly flesh. I've seen kydex adorned with 100MPH tape to hold it together and wanted to avoid that problem. Further testing is in progress and while I have preliminary reports, I'd like to end testing before a final write-up. IMHO Andrew made one hell of a sheath, and I would not hesitate to carry it almost anywhere. The qualifier exists because we are convinced it will fail below -20F but do not yet know exactly how that failure will manifest itself.

I am agreeable to a passaround if Andrew agrees.
-carl
 
Originally posted by Carl Theile
The qualifier exists because we are convinced it will fail below -20F but do not yet know exactly how that failure will manifest itself.
Click to expand...

If you're really curious, get some alcohol, and chill with dry ice. Manipulating the type of alcohol and mixture can get you down to about -40 (don't remember if it's Fahrenheit or Celsius), so -20 is definitely doable. I have a feeling that your choice of glue would make a big difference at low temperatures. If you want more specifics on the dry ice/alcohol bath, let me know and I'll do some research.
 
I have spoken to Andrew about this sheath and am interested in having one made. I am encouraged by the testing that has taken place to date. I think this method of construction combined with a Cordura outer covering like the Eagle and SOE sheths holds promise for hard use applications, especially in my line of work.
I would really like to get my mitts on one. :D

Nick

~Nuclear INFIdel and Aspiring INFI Hog~
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Originally posted by Tohatchi NM
If you're really curious, get some alcohol, and chill with dry ice. Manipulating the type of alcohol and mixture can get you down to about -40 (don't remember if it's Fahrenheit or Celsius), so -20 is definitely doable. I have a feeling that your choice of glue would make a big difference at low temperatures. If you want more specifics on the dry ice/alcohol bath, let me know and I'll do some research.
Click to expand...

The funny thing about -40 degrees is that -40 degrees Fahrenheit = -40 degrees Celcius. :)

So, I'd say the -40 is almost -40 on either scale.

Unless you throw Kelvin into the mix, but negative temperatures (even 0) is impossible on that scale.

For those who are interested, the formula is F = (9/5) * C + 32

Or

C = (5/9) * (F - 32)

and for reference:

K = C + 273.15
 
Great work Andrew there is too much over hype on the toughness of 0.060" Kydex. It is good to see some real progress being made in dealing with the brittleness and lack of ductility of Kydex especially at cold temperatures.

As for dry ice, I use it on a semi-regular basis, if used in a bath it will normalize at close to -80 C. You can get intermediate temperatures with it and liquid nitrogen by making slushes but these are not trivial to use and it is very easy to go too far or not far enough.

-Cliff
 
Guys-
Thanks for the information. Our attempts to achieve temperatures lower than -20 and importantly, get the entire product at those temperatures so as not to introduce thermal stress as a factor, were feeble and/or uncertain. So the objective, now, is to go to progressively lower temperatures with "through and through" cooling.

We believe we are already working well below temperatures that normally produce failure in kydex. We were able to proceed to this point in graduated steps. We are concerned that the next "step" is large and as we feel we are at or near the limits of what the product will take, we are reluctant to leap to the -40 or -60 mark. We would like to come away from this test knowing the exact temperature at which it fails.

Anything you can recommend given that guideline will be appreciated.
-carl
 
Good news and bad news. I found a liquid that freezes spot-on at -20F . The bad news is that it's concentrated Hydrochloric Acid, which would be really nasty to work with.

Option 2: Carbon tetrachloride, which you can't get any more because it eats ozone.

Looks like the best option is dry ice in alcohol or acetone (both available in 5 gallon cans at a hardware store). Dry ice will cool down to -78C, so you could get the bath really cold,dunk the sheath in, and wait for everything to warm to -20. This requires an accurate thermometer that reads that low. Probably cost $10.
 
Tohatchi NM
I understand the cool down/allow to warm to the desired temp concept, but trip over the concern that I may have an unknown temperature differential inside to out, or core to outside. That is why I was looking for a way to achieve a constant temp through and through...

Maybe I am just making much out of nothing...
-carl
 
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