Most knife sharpening kits that you can buy can damage or scratch your knife. The professionals always recommend using a set of sharpening stones, such as Arkansas stones, wetstones, or waterstones. However these stones often run $40+ and even more for a good sized one. These stones also have the problem of developing a "bowl" shape after repeated use, which in turn requires you to buy another stone - a flattening stone. As you can guess, buying these variety of stones becomes extremely expensive.
The knife sharpening kit that I made is capable of making a knife sharp enough to shave with, utilizes easily obtainable parts, and never goes bad or develops "bowl"-ing problems. Some quick repair/maintenance and the knife sharpening kit is as good as new, with minimal costs.

Step 1: Materials

So the basic idea behind this, is that you will be attaching sandpaper onto bathroom tiles, in order to create DIY sharpening stones. Simple, and it works. The best part is, that you can replace the sandpaper whenever they get old, really easily.

Materials Needed:
Container of Acetone ~ $10?
Spray Adhesive - $10
A variety of high grit sandpaper - $3/(pack of 5 sheets) * 5 packs = $15
cotton cloths (or cut up an old t-shirt) - Free
rubber bumpers (optional) - $3
smooth bathroom tiles - $0.80/tile *5 = $4

The high grit sandpaper can be found at automotive stores, or in the automotive section at Walmart. For those that done know, the higher the grit number, the finer sanding. You'll want 800, 1000, and 2000 grit sand paper at least. 200-400 grit sand paper would be used for a really dull, dinged up, and damaged knife that you want to remove nicks from. Though at 200 grit, you may as well use a dremel with grinding bit. While 2000 grit sand paper will give you a knife that you can shave hairs off with, if you are sharpening a straight razor and actually plan to shave with your blade, you may need to order higher grit sandpaper (4000 grit).

You'll want as large (long) of these sand paper sheets that you can find, and then get the smoothest bathroom tiles that you can find, that will fit these sheets of sandpaper. The sandpaper sheets that I found were 3.5" x 9" and the tiles I found were 4" x 8".

Everything else on the list can be found at a Lowes/Home Depot. The cotton cloths can be found in the painting section there.

Step 2: Prep/Cleaning

So you'll want to do this in a relatively clean area, with no wind. I chose to use my bathroom as it seemed like the best place. Though, word of caution - don't stay in an enclosed area with and open container of acetone for very long, and turn on a vent as soon as you attach the sandpaper sheets.

First, get your cloth rag and put a little bit of acetone on it, and clean the bathroom tiles. You want to make them clean, and free of any fuzzies. Give them a few minutes for the acetone to flash off of the tiles.

Step 3: Attach Sandpaper

Setup an area where you can spray the adhesive. Spray both the bathroom tile, and the back of the sandpaper sheet, and attach them. After messing around with this sharpening kit for a while, I found that I preferred the sand paper to be on the edge of the tile, as shown in the third picture, but you may just have to try it to find out what you like best.

After you have attached the sandpaper to the tile, quickly get your cotton with acetone on it and remove the spray adhesive from the rest of the tile.

Then place something over it that wont attach to spray adhesive or would be easily removed (wax paper, plastic, etc) and put a large flat weight on it to compress the sandpaper sheet onto the tile, and let it sit and cure. I used a sheet of plastic from a package of computer paper, placed a book on top of it, and then put on 20 lbs from a weight set on top of it.

Rinse and repeat for each set of sandpaper that you use. Use a sharpie to label each tile. Remember, when you are sharpening there will be water on these, so you don't want to have to turn them over to see which sharpening tile you are using.

Let the spray adhesive cure for an hour or two before you start using these sharpening tiles to sharpen your knives.

Step 4: Results/Conclusions/Suggestions

I recommend putting some of those little rubber bumpers on the bottom of these tiles, so that you can stack the tiles without worrying about damaging the sandpaper sheets. It also has the added benefit of making it easier to sharpen your knives without the sharpening tile moving.

As I mentioned before, while trying out this sharpening kit, I found it more convenient to have the sand paper flush with the edge of the tiles, and to have the excess sand paper cut off from the tiles.

If the sandpaper ever becomes damaged or old, its easy to replace. Just peel the sand paper off and remove the adhesive using the cotton cloth and acetone. The spray adhesive seems to be acetone-soluble.

After you've sharpened your blade using the 2000 grit, you feel that it is still not sharp enough - you could get some higher grit sandpaper, or you could lap the the blade a few times using an old belt, or and old pair of blue jeans. Just cut up some blue jeans and lap the blade like you would see a barber do with a straight razor.

Important: recommended sharpening method
So I used this sharpening kit to sharpen my kitchen knife set, and learned somethings doing so. If you don't know how to sharpen a knife using a sharpening stone / whetstone, etc watch some YouTube videos on how to do so. When you are sharpening using this kit, you only want to PULL the knife back as you sharpen it - as in don't push the knife, sharp edge first, forward to sharpen it. This will prevent damage to the sand paper, and extend its life.

Use water as a lubricant. Sharpening stones often required you to use some kind of oil or soapy material, sometimes water. Since the sand paper is wet or dry type, just use water - that's what it was made for.

Final Thoughts:
So I've used this sharpening kit to sharpen all of my kitchen knives, my pocket knife, and a bayonet and have been very pleased with the results. After sharpening 75% of those items, I had to change the sand paper on the 800, 1000, and 2000 grit, because they received some damage while I was learning the above recommend sharpening techniques. Btw, the 800, 1000, and 2000 will be your most used grits/tiles. Anything less than that is more used for major repair.

Remember - be careful with sharp objects! Don't cut yourself. I'm not responsible for any damage to yourself, others, creatures, or objects.