Of the two materials, it is easier and faster to make a reasonable sheath from Kydex than it is from leather.
There is no such thing as free lunch
In order to work Kydex to that reasonable level, you need a few more tools than you do for the leather work. They don't have to be really expensive tools, but they can be a pain to gather together.
You need a paint stripper type heat gun. You can do the initial heating in an oven, I didn't like it, but some folk do. However, after having done the moulding, you may need to carry out some localised tweaks to adjust tension, and for that you need the heat gun.
Thin cotton gloves to allow you to handle the hot plastic without being burned
A foam lined press. www.knifekits.com (and others) sell a 1inch thick heat resistant foam for press linings. Some people say that you can use the blue foam kip mats from camping shops. I tried and the dang stuff melted and stuck to the Kydex. It also had a memory which meant that it didn't stay flat for me after the first exposure to heat and pressure. Clamping can be done in a hefty vice between thick bits of plywood, or in a hinged press. Speed is needed, so plywood with a G-clamp at each corner isn't going to work all that well, the quick grip clamps might work better. Some people say that they just stand on the "press" and use un-aided body weight, but most authorities say you can't get enough pressure to to a good job. That's been my experience too.
Extra bits...eyelets for use with Tekloks need to be the correct size, about 1/4 outer diameter and about 5mm inner. I have only ever seen these from places like KnifeKits, but suppose that they might be found on Ebay. The ones sold by The Identity Store aren't quite right. However, TIS does sell Chicago screws in the right sizes and finishes. If you use eyelets you need a setting tool.
Other tools, rules, scribes, correct drill bits, drill, saw, files, fine sand paper (the premium stuff which doesn't shed its grit easily is WELL worth using, you don't want that grit getting into the sheath before you are even finished!)
Masking tape for giving clearance around the blade.
There are some tutorials on the net. A few threads are available on the US Knife forums, and there are plenty of question and answer type threads there, and on British Blades.
Cutting Kydex, a straight edge and Stanley knife can be used to cut part way through in straight lines, before flexing and snapping the rest of the way. If done right this gives a nice straight, clean, cut. Cutting curves, a band saw would be nice, a scroll saw maybe, but you can do pretty well with a 32tpi hacksaw or coping saw. The cut will be rough and need cleaning up with a file or sandpaper. Don't put too much friction in otherwise the plastic softens a little.
One Square Foot of Kydex should provide enough for three sheaths for 4" bushcraft knives, if you use a Teklok, but probably only two if you need it for belt loops too. Personally I like using the thicker 0.09" stuff for belt loops since the stiffness really helps.
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