Theres alot more info on this in the shoptalk forum(under general discussion, a few down from the top). You may have to do a search, I think there are still a few threads going on it but some of the real good stuff is archived.
I have had mixed success making kydex sheaths. I don't have a clue what a stinger is, you may be better off trying to make a sheath for something different until you've got a good handle on things. Some shapes are easier than others.
Heres what I've found to be easiest.
A two peice sheath, formed from 2 rectangles(front and back)done in stages.
Start off and get the basic dimension of your knife/tool and leaving your self lots of space, cut a recatangle with the largest dimensions. Do the same for the back peice adding a belt loop or whatever you need to it, it might end up L shaped.
For the molding, heat your front peice first, center your knife/tool on it and press it in the foam until it cools(I use foam thats about 3/4" thick, and have one ontop of the knife/sheath and one underneath, press from both sides). Plan ahead, I ended up with a left handed sheath on accident once.
Set that peice off to the side and repeat the process with the back peice, don't worry about the belt loop yet. (pay attention to which side of the kydex is facing up, you don't want to use it inside out)
Now that both peices are fairly well molded to the knife and cooled off again, you can put the knife in between them and everything lines up. As long as they lay together flat you can put some rivets in . Now heat the whole thing, put the knife in and press it again to true up the fit.
Use your bandsaw or whatever you have to cut it with and rough out the profile of the sheath now, add more rivets if you need too.
Lastly, heat up the section of kydex for the belt loop and shape it. I like to use a dowel rod to form the fold so its not to sharp (makes it weak if you crease it too much). I've had the best luck with folding it over once and putting a rivet or two in to close it off.
Sand edges, and adjust things the way you want and your done.
I forgot to mention that I do all this with a heat gun instead of an oven. You may have to change things here and there since you can't spot heat with an oven. You could still try doing the front and back seperate though. A lot less forming to try and get done before it cools off.
