I started making sheaths because I wasn't happy with factory sheath. I have made leather and Kydex® and prefer Kydex® because it doesn't absorb moisture like leather does. I didn't/don't have a shop to work in so I tried to simplify the process as much as I could with the simplest tools as possible.
Step 1: Try This at Your Own Risk.
To begin I want to say I work with heat sharp objects and other things that can and will hurt if used or done incorrectly. If you choose to duplicate anything I do or have done it is at your own risk. If you hurt your self or others or damage anything I take no responsibility for your actions.
Step 2: Supplies
The things I use include the knife to mold, Kydex®, a pencil, a straight edge, a foam press, gloves, cookie sheet, oven, a multi-tool, sand paper, rivets/rivets and set (you can substitute Chicago screws), a drill and bits, and a heat gun.
Step 3: The Press
I have seen some really cool and creative presses. This isn't one of them its pure function. All it is is two pieces of 3\4" plywood with foam in the middle. The foam used is from a cheap camping pad scraps (the bulk of the foam was used on another project and you can buy them for about 5 bucks). Once you have your wood cut to the size you want your press, you can glue or leave loose the foam its up to you I used rubber cement for mine. I found its easier to work with two rather than 6 pieces when working with heated Kydex®.
Step 4: Getting Your Kydex® Ready.
I used a piece that already had had some of the sheet taken. The sheet I used is 0.060 Kydex®. Once I lay my knife to be molded out I leave a bit of extra room as Kydex® seems to shrink up a bit. Once that's done its time to prep the oven.
Step 5: Heating
I normally set the oven between 275 and 300. Then I flip over a cookie sheet and lay the Kydex® on the back with the smooth side down. Once the pre-heat is done I pop the Kydex® in for three to five min. You will know its done because it will bend really easy and flop under its own weight Lasagna noodles are pretty good comparison.
Step 6: To the Press
Gloves that can handle the heat are a staple for me at this point. When the Kydex® comes out of the oven you have just a couple moments before it starts to cool and harden back up. Get it to the press and get the knife you are molding lined up. In this case I made a fold over sheath for a Boker Tuf®. After the press is closed stand on it for 5 to 10 min. some people use clamps or straps they all work.
Step 7: Shaping the Sheath.
Using a pencil I line out the final shape of the sheath on Kydex®. Using a knife I score the the Kydex following my line. Then using the pliers I break of the exess.
Step 8: Laying Out Your Holes for Rivets.
Hole spacing is up to you I prefer 3/4" on center. I begin by pinching the sheath to add pressure to the Kydex® to try to find the spot that lets the knife hold fast but it can still be removed comfortably. This is where i place my top most hole. Once you have set the hole spacing get the drill out and make the holes use the bit that matches the rivets, grommets, or Chicago screws you will be using. Don't forget to clear any excess snibits from the holes.
Step 9: Shave and Sand.
Once my holes are drilled I make sure my edges are smoothed and rounded and the interior is rinsed out, before I set rivets or eyelets. Once assembled it's hard to get the debris from sanding the edges out of the sheath. so At times i also have to trim the edges to flush with my knife before I sand them
Step 10: Checking Your Fit.
At this point the sheath is pretty much done I double check the fit and if needed use a heat gun to add a thumb stop on the back of the sheath to aid in drawing the knife.
Step 11: Add a Clip or Not
I use the G clips on a lot of my sheaths because of ease of build and use. You can also make a leather or nylon harness to bolt the Kydex too for many other carry options.