I recieved an email the other day on how I lap the soles of my planes. Here is my technique.
To many woodworkers, the process of taking a brand new plane, or even an older one, and spending a couple hours on tuning it seems to be a waste of time. This is just not true. Whether it is brand spanking new, or 200 years old, a planes sole has to be lapped for it to work correctly.
A properly tuned plane will glide through the wood with remarkable ease. Even planning the end of a board will be successful. The shavings coming out of the plane will be fine enough to see through!
The first step in tuning any plane is checking the "sole" or bottom of the plane, for flatness. This can be accomplished with a steel straightedge. Lay it diagonally across the sole and look for any light between the straightedge and the plane. Take note to any hollows. Now lay it across the other diagonal corners and check that. Again, take note of any hollow areas. Using the same technique check the front to back flatness on both sides of the sole. The object here is to determine if the sole is dead flat. If it isn't, and most often it isn't, you'll need to flatten it.
Using a piece of 3/8" plate glass, wet it with some mineral spirits, and lay some wet / dry sandpaper on it. The mineral spirits will hold the paper tight to the glass. It will also act as a lubricant while flattening the bottom. The grit of the paper is determined by how bad the bottom is. I would start with 220, that is the way I work. Everyone will tell you something different, it just depends on the severity of flatness. Now you can buy a kit from Rockler for 33 bucks that will have everything you need to stat lapping, and honing irons.
Holding the plane firmly against the paper, rub it back and forth a few times. You will notice some spots are shinny, and some parts are still dull. They way I do it is sand until the whole surface is shinny, or flat. This really only has to be done when you first get it. Anything from here on out will have this flatness as its reference. This sounds harder than it actually is.
Once you have the sole flat, switch to finer sandpaper and start the polishing process. By working your way through the various grits of paper, going finer and finer, the bottom will become polished. I usually take mine to a mirror finish. The good news is once this has been done, restoring it to the same condition later will take only a few minutes.