Just thought I'd share this after reading a post from a month or so ago about hunting knives. I've been using PVC pipe to make sheaths for knives for years. I've made sheaths for machetes to bait knives. All my fishing filet knives have these.
Disclaimer: You can get your knife permanently entombed in these when your making them if you're not careful! You can stick the PVC back in the oven, but that may damage your handle - so think this thru before starting! It is best to first experiment with one of your wife's good kitchen knives
or better maybe an old screwdriver if you want to practice.
Get a piece of PVC pipe a little longer - maybe 2" longer than the exposed steel on your knife. You can use any diameter, but if you can get a diameter that the knife blade just barely fits in, or a little small, is the best. The schedule 20 lightweight is the best - lighter than schedule 40 but still plenty durable.
Stick the pipe in a toaster oven set on no more than 300F. Any hotter and you'll burn the stuff and it produces very toxic fumes.
Check to see when it softens. While you're waiting, get a couple pieces of lumber - 1x or 2x4 is good, unless you have a machete, then you need something wider, like a 1x6.
You're going to smash the softened PVC around the knife blade with the lumber - so it just needs to be as long as the knife blade or a little longer.
Also, good to wear some gloves - leather or thick cotton.
When the PVC softens, it can get pretty soft, but you don't need it really really soft. If you take it out too early, you can stick it back in again - I think as many times as you want.
When you think it's soft enough, take it out and quickly stick your knife blade inside, with the end coming over the handle a little bit. You may need to fiddle with it a bit to get the handle inside if you've got small pipe, but if its soft enough, you've got 15 seconds or so before it cools off too much.
Don't stick the handle in too far, and you'll have to keep the PVC from closing in around your handle too much - you have to be able to pull the knife out, so use your fingers to stretch the PVC if needed. You're making kind of a funnel for the handle to seat in.
Before the PVC cools, put the part of the PVC with the blade in it on top of one of the pieces of wood, take the other piece of wood and smash the PVC around the knife. You don't need to push too hard, but it can touch the steel and won't stick.
You do need to be sure the knife will slip out - so if your knife is got a gut hook or has some weird shape, this won't work. Also be sure the PVC doesn't close in behind your handle, or it won't come out. You can take a hot air gun (torches don't work - burns the PVC) and heat the PVC while shielding your knife handle to shape it how you like.
You need to hold the lumber pressed together for a minute to let the PVC cool down enough to stiffen up. It stiffens when the PVC is still too hot to touch.
As soon as you can, pull your knife out. If you can't pull it out, you maybe be in trouble. It is probably stuck around the handle, and you can carefully trim the end with a front cutting wire pliers or tin snips, or if your handle can take the heat (most probably can't), stick it back in the oven with the knife in it.
Hope this helps someone.