This is really easy and is great for adding stowage to tanks/bikes etc or simply terrain or objective markers.
These can be made any size really but the example I'm doing is aimed to fit the Space Marine Scout Bikers.
I'll show the basic steps for both and then at a certain point we will focus on one and then the other but the basic steps are the same. Even so both of them are still what I would term a "basic" version, there is so much you can do with them in terms of adding more detail.
So we start off with some bits of plasticard shaped roughly to be the same size and shape as your desired object, generally 1 mm smaller, don't worry it doesn't have to be exact as we will be covering it in greenstuff. This is to give a small bit of texture to simulate leather or cloth. For these ones I have used a bit of 1mm thick plasticard shaped to be just a little smaller than the example knife.
Now you can make these in situ so to speak on the bike or whatever they will end up on and this is easier but for the purposes of this I'm going to isolate them, if you are going to do the same then get a bit of sprue and stick the plasticard to it, super glue or plastic glue, it doesn't really matter just don't use too much of it as you will need to remove them from the sprue!
Now get your modelling putty, be it grey, green, brown, whatever it doesn't really matter and mix it up well. It really doesn't matter what type you use as its not really fine detail we need. I've used both grey stuff and milliput and both work just as well.
Wrap the putty around the plasticard. You do want to use a good bit, especially if you are going to start shaping it. Smooth it out so that it should look like this:
Finger prints aren't necessarily a big deal, especially on knife sheaths as we will end up filing down the flat surfaces, its mainly the rounded edges that we want and the little unevenness of the surface that the putty gives but is hard to get with just a bit of plasticard.
Here is where we leave the knife sheath to dry, that's basically done now we just need to add the extra details, however if you want to before it dries you can add stitching to the edges like the Space Wolves ones (just use your sculpting tool or knife edge to get the mark you want and replicate it) or you can add further folds to the "leather".
So to the bag. I'm going to do a satchel style, something that I can imagine being used to store clips or something. What you want to do is get your sculpting tool and about 2/3rds of the way up press in and shape the piece into two levels, the thinner one being the higher. If you've used a good amount of putty you shouldn't have a problem with this step. Remember its always easier to take excess stuff away that it is to add more to it when working with putty. You can do it another way which is to add another strip of putty to the top 3rd and get your two levels that way.
Now what you want to do is tidy it up. If you want the flap straight make it straight, if you want it curved well you get the point. Get the edges flat on the sides and top but don't worry about the back as we will easily remove that with a file or knife once it has dry.
Now you can leave it to dry or make it into multiple pouches, like this:
Now leave it to dry.
So we are ready to start adding the details to it, straps etc. We will start with the pouch. It should look exactly like the image above but just be dry. For this next step you will need some plasticard again but this time I used 0.10" or .25mm thick card. Take your piece and cut into into two thin strips. One say 2mm and the other 1mm.
I also use a 0.88mm strip of rod for rivets, poppers etc. So here are your collected materials:
Take the 2mm strip and cut two bits off between 3-4mm glue them where shown:
You can glue them over the lip as well or just do them as I have then take the smaller strip and place it along the edge of the lip.
Trim it to fit.
Now take your rod and slice some rounds off it about 1mm thick if you can.
Glue these in place like so, these are the attachment buckle things.
I've also drilled a pair of holes in the plasticard strip to show room for adjustment. I do this after I've glued the strip as its so thin that it could break if you do it before hand. The trick is to make sure you don't go too deep.
As I said this is just the basics, you can make many of these, all different with very little effort. Some more detailed with the straps over hanging etc as you can see looking at it from a low angle the gap shows, however on the TT you won't be able to tell especially once it's painted.
Knife Step 6
So onto the knife sheath now. After the greenstuff has dried you want to take the sheath and give it a bit of a smooth and file:
Knife Step 7
Now take some plasticard like we were using earlier:
Take one of those smaller thin strips and wrap it around the top of sheath to create a water guard. The best way I find to do this is to place it facing long wise first and then wrap the rest around and cut to fit. You can smooth the corners later. I use superglue for this. Plastic glue will work but it does take a lot longer than normal to dry.
You can also use greenstuff to do this, wrap a tube around, smooth out and square off but this way is quicker.
Knife Step 8
Now take 2 of the thinnest strips we cut and wrap them around the knife sheet in the same way as before. Do this about 1mm from the water guard and then another 2-3mm below that. These will be the straps. See below:
Knife Step 9
Now take that thin strip again and cut off 2 square pieces and stick them onto those strap lines:
I then also stick some of those 0.88mm rivets on top of them
Knife Step 10
Now you can leave it at that but I add one final thing to it. I'm also adding a pouch. So take a strip of the plasticard that we used for the water guard and wrap it around again, this time at about the 1/3rd line from the bottom. Also take a pouch from either an Imperial Guard belt or one of the ones from the Space Marine Tactical Squad like I have... or you can build one using the same method as the previous tute shows.
Stick the pouch onto that strip of card. Done:
There we go, I hope this has helped you out. This method isn't restricted to knives either, I've used it for shotguns as well.