This is my first instructable. I was bored one afternoon when i was off college so i decided to make a scalpel and share how i did it. I'll have to warn you though, before i continue: this thing is as sharp as you make it. I also blued mine, with nasty toxic bluing solution. Be safe
Step 1: Make and Mark the basic shape
I snapped off a piece of carbon steel hacksaw blade aboout 3 inches long, that's 10 CMs. I chose a piece form the end of the blade becasue it's got a hole in the end, and that might come in useful for something. I used a marker pen to mark the bits i wanted to grind away. My camera's not that good, so you can't see that I marked the teeth of the blade too.
Step 2: Grind the shape
Using a bench grinder (sorry, but I couldn't figure out how to add steps of the tools and stuff you'll need. It's all here, though but you have to look for it. Sorry.) grind away the marked bits of steel. You should grind the curve of the blade, remove the teeth and grind a hollow for you finger to go into. The finger-hole thing's not really needed, but it's good to have it. Really it's only the blade you need to pay serious attention to, you can make the rest of it to your taste.
Step 3: Remove the paint, rust, oil, other crusty stuff.....
After you've ground the blade to its shape, you'll need to sand it down. This has 2 functions, 1: it removes the burrs (fluffed-up meta) from the grinding. I already forgot to tell you that when you're grinding, dip the metal in water every 2 seconds. If it gets too hot, it'll lose its temper and become too soft to keep an edge for any great length of time, and a scalpel's job is to cut. Soft metal won't cut well enough.
The second reason for sanding is to remove the paint from the blade. If you have ruined the temper, it'll probably show up here as discolouration. I used a piece of porous breezeblock (cinder block for Americans, I think) but fine sandpaper, of even a soft stone work just as well.
Step 4: Sharpen!
Back to the grinder. Gently stroke the bit you want to be the blade along the fines grinding wheel you have. Once or twice per side should do it, remember, the steel you're using is very thin, so will grind down very quickly. Watch that temper, there's no excuses. After you've finished grinding, start on an oilstone. You want to remove all the scratches from the grinder. Sharpen both sides of the blade. If you sharpen properly, you'll get a razor sharp edge, but you need to be patient. Sharpen as much or as little as you want. Sharp edges cut better but wear down quickly. Blunter edges don't cut as well, but last longer. Considering how thin the steel is, it's worth putting a REALLY sharp edge on. It doesn't take long....I think there's an instructable on sharpening somewhere.....You can't see in this blurry and nasty photo, but the sharp edge of the blade is fully formed. If you want to, stop here, your scalpel is complete and there's not point continuing. Don't do anything stupid, blah blah blah. For those so inclined, go to the next step.
Step 5: Bluing the blade
This step isn't really needed, but i did it so the scalpel looks cooler, and won't rust as easily. Apply the bluing solution of your choice to the blade, and follow the instructions to get the best results. Once you've finished bluing the blade, sharpen the edge again. I'm not sure how bluing solution works, but i suspect that there's a little corrosion to form a skin of oxides on the steel. Sharpen the edge again to remove this layer. Be careful not to scratch the flat bit, otherwise it'll look shoddy and ameturish (not sure how to spell that) Congratulations, you've just made a scalpel, don't do anything stupid. If you've got anything pertinent to add to this, please comment. Thanks for reading through my needlessly wordy instructable, i'll have some more at some point.