Draw out a simple knife design on paper. For this exercise keep the blade length between 3" and 4" and the handle between 4" and 5". This probably isn't your dream knife, it'll just be something simple to learn how to forge--something which, hopefully, won't be too embarrassing.
Transfer your design to 1/8 Masonite and cut out. Call it the Knife Blank.
Two tools which are very useful in knife forging: American Standard Wire Gauge and Protractor. The wire gauge is available at most places selling jeweler's supplies. Use it to measure the thickness of the blade edge. Use the protractor to measure the cross-sectional angle of the blade. You can also get it from ACE Hardware, at the home page enter the item # 26322. Both are made by General Tools.
American Standard Wire Gauge is abbreviated as AWG and we'll use this abbreviation throughout. More information on AWG for the terminally curious.
The protractor needs to be modified to serve our purposes. Punch out the rivet holding the movable arm, turn the arm over and reinstall the rivet. Mine was held by a small washer that I could tap back into place. You'll now take the blade angle measurement by placing it on the metric side of the ruler.
The reason the wire gauge works particularly well in gauging edge thickness is that the measurement is taken at a preset distance from the actual edge. With a micrometer it's hard to know how far in from the edge to take the reading and then you need an extra hand or two to do so. Also it's a snap to gauge the entire length of the blade edge just by drawing the gauge along the entire length. It's a quick and accurate way to make sure blade thickness is uniform.
Use the wire gauge and protractor to measure blades to find out how they fit into the graphs below. Measure as wide a range as you can.
This graph displays the proportional correlation between blade thickness and edge size. It tells you which stock thicknesses to use with which edge sizes. All examples in this tutorial will use a finished edge thickness of AWG #16, so plan to forge from stock an 1/8" thick by an inch wide. As we'll see in more detail later, edge thickness determines blade geometry in respect to angles and thicknesses. Edge thickness is the place to start when designing. This measurement establishes how a knife will cut and how much strain it can withstand. Once edge thickness is chosen, everything else pretty much follows. When designing knives, the edge shouldn't be the last thing to consider--it should be the first. Because at the end of the day, a knife is just a glorified edge. Decide what kind of edge you want and all the rest follows naturally.
Blade Angle plotted against Edge Thickness using wire gauge and protractor.
The formula is Blade Angle = 25-AWG