Das hatte Bob Engnath auf seiner Tips-Webseite zum Thema stehen:
"KYDEX FOR SHEATHS
Kydex is a thermo forming type of plastic that was developed as a tough wall covering for institutional use, but it just happens to make a very nice knife sheath.
Bob Terzola started using this for sheaths while he was living in Central America. He says that it's about the only thing that won't rot in the jungle, and there aren't any critters that are particularly fond of eating it. You won't find some porcupine munching on it when you leave the sheath out overnight in your camp.
Kydex has to be heated to around 400 degrees F. to make use of its' hot molding properties. You should use a toaster oven to warm it, and gardening gloves to handle it while it's hot, unless you like having scorched fingertips.
You may form it directly to the knife, or use a mold made of wood. The wood mold method has already been published, so I'll concentrate on the other style.
Hunting knives need Kydex about .060 thick. If you're making a sheath for a much larger knife, try using .090 thick for extra strength and stiffness. You may mix thickness of material within a sheath to get a stiff back and flexible front if you like. Gun holsters use the .090 thickness. We stock only black Kydex in .060 and .090, but will order other sizes or thicknesses if the quantity is enough.
You have to assemble a bunch of gear. A heat gun is essential. You need two slabs of plywood, 3/4 inch or thicker, with half inch thick foam pads on one side. Terzola suggested "outsole neoprene sponge crepe", available at shoemakers' a supply in 18 by 36 inch slabs. Make the plywood about two inches longer than you'll need for the largest sheath that you plan to make. The foam recommended is tough and should last for fifty or a hundred heavy pressings. Spray both foam and sheath with WD 40 occasionally to keep things from sticking. Ordinary mattress or pillow type stuff will not work. Use brass shim stock for making heat shields. (I'll explain them later.)
The blade portion of the knife should have a single layer of masking tape covering it when you start. Also, if not already understood, a blade with any sort of notches, choil cuts, or widening belly towards the tip, will not work with the mold-onto-the-blade method. Kydex will also mold into sandblasted texture or even an etched logo if you're not careful.
Put the toaster oven right behind the vise and get the Kydex hot. The Kydex should have been roughly cut to the shape you'll need for the sheath. Most sheath makers use cardboard patterns, so cut around the pattern with a generous margin. You literally have to rivet any extra parts to a Kydex sheath, using eyelets, so plan ahead. Kydex may be cut on the bandsaw, using a narrow, fine tooth blade turned backwards. A tin snips works well if you haven't got a bandsaw.
You can't just score Kydex like leather. You actually have to take a Vee cut of material right out of Kydex to make it work right. Use a matt knife with a blade designed to cut laminate. Kydex may be folded into many shapes, but will not twist very well.
Kydex works best when heated by convection (air), rather than radiant or infrared heat. Convection heating will allow the whole thickness of the material to warm at the same time, which is what you want. Cover the Kydex with aluminum foil to get the right heating. Higher heat gives more flexibility.
Have the padded boards ready in the vise, with it open far enough so you can slip in the plastic and knife. As soon as the Kydex is hot, grab it, slap the knife into position, slip the package into the opening between the padded boards and clamp down with the vise. You have to do this all in about two seconds, before the plastic cools. Don't be afraid to really clamp down with the vise. You can't hurt it. Cooling time is around 20 seconds.
Now you have a partially formed sheath, a U shaped trough of plastic. Remove the knife. Put small spring clamps on the edges to hold things in place. Re-heat the Kydex and repeat the whole procedure for the final fit to the blade. You shove the blade back into the sheath as you move the plastic from the oven to the press setup. Pull off the spring clamps as the press boards are clamped together.
Kydex has a memory. When you put it back in the oven to heat it to form the belt loop, it will try to go flat, and the kids will hear some of those words again. The second pressing will get the plastic to such a tight fit that you can see the texture of the tape on the blade through the plastic. Any more forming has to be done with a heat gun.
Trim the sheath parts. You can use a knife or a grinder. Figure out what parts you'll want to get hot, and which areas should stay cold. Make a shim stock shield to protect the parts you want to stay cool. Heat the necessary area with your heat gun and form the belt loop. A wooden form is really handy to make crisp bends because the wood won't cool the Kydex too quickly.
Terzola uses a dimple in the side of the guard to lock the knife in the sheath. He cuts a precise dimple with a half round ended milling tool, on the outer side of the guard. As the sheath is molded, the dimple partially forms into the Kydex. He finishes the forming with a heated, round ended tool. Once the dimple is matched with a molded in mate in the side of the sheath, the knife is in there until you actually pull the Kydex away from the guard 'socket'.
Ed Halligan makes a neat little knife that is hung around the neck, upside down, in a Kydex sheath. His pattern is very plain, so there are no undercuts or dimples to help hold it in the sheath. He makes it work by fastening the grip on with oval head screws. The sheath goes down over the front pair, and the rounded heads mold into the kydex well enough to hold the knife securely. He also uses kydex for the grip, simply two slabs of 1/8th inch stock screwed on. Makes a neat and inexpensive knife.
Fasten the welt area together with grommets. This plastic doesn't glue very well, but A B S pipe bonder works to some degree. but can't stand much flexing Now we have a report from Ed Halligan that the solvent T H F (tetrahydrofuran) will weld kydex very well. Our test indicates that you need to saturate the joint thoroughly and clamp it lightly for at least a couple hours. T H F is not one of the "user friendly" solvents. "Black Max" from Locktite, is also reported to work on kydex.
If you plan a slant belt loop, or fancy release system, try making a few mock-ups in cardboard before trying it in plastic. Pay particular attention to how things will have to be done after the second pressing has the blade portion completely formed and you get into the tricky bends.
Medium thickness Kydex, .060, will form its' own belt clips that hold as well as the metal ones if you form them right. The heavier stock, .090, will darn near need a pliers to get the loop off your belt. Form the belt loop so about an inch of plastic goes up under the belt and there is no need to rivet the end of the plastic down. A belt loop should be about an inch and a half wide to hold well. You can use the .090 thickness Kydex if you want a loop that'll hold a small vehicle.
Finishing the edge of the sheath may be done with a fine belt or a small "Scotch Brite" wheel. Don't forget to tape the mouth of the sheath closed when working on it with power tools. You don't want any grit in there because it would scratch the blade.
Kydex is not particularly kind to a blades finish, and you are sure to get some scratches eventually, from stuff that just falls into the sheath. Don't use Kydex with art knives, or those that are mirror finished.
Kydex is a fascinating material and needs to be explored much more before knife makers find all of the uses and variations possible.
A note. I tried a bunch of sheaths years back, using Velcro strap closures. It was a nice, high tech material, so I thought it was sort of neat. They didn't sell. Velcro is not a quiet material to open, and most people hate the noise it makes. In the woods, or battlefield, silence is essential. Kydex is not as stealthy as good ole' leather because the fit is mechanical, and some part is going to spring back.
The Kydex sheath may also be covered with a glued on layer of leather or fabric. It also comes in quite a variety of colors.
This web page was created by Zoe Martin
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