This is an idea I ripped off from the ancient Mesopotamians, so I don't think anyone is alive who can sue me.
The wood I use for these is normally small pored (not Oak, or any similar large pored wood) and of medium hardness. This makes the cylinders soft enough to be carveable, but hard enough not to deform under pressure. To that end, Walnut is ideal, although I have made cylinders from Padauk (pictured), California Bay Laurel, and Yellowheart. Yellowheart was a little too hard, I don't want to do that again!
I cut cylinders of wood out of thick blocks with a hole saw in a three step process.
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Step 1: The Pilot Hole
First, I drill a pilot hole all the way through the wood. This should be either the same size, or smaller than the pilot drill at the center of your hole saw. I generally take a precut cylinder, and place it on the wood to figure out where to put the pilot hole, as I don't want the hole too close to the edge and making a flat area, although having it near the edge allows the sawdust to escape, and lessens heat and resistance. Rubbing a little beeswax on the side of the holesaw also helps.
Step 2: First Cut With the Hole Saw
I use the pilot hole to start the hole saw, running it down as far as it will go, and lubricating it with beeswax. The depth of the hole saw should be more than half the thickness of the wood, otherwise you won't be able to get the cylinder out without resorting to a bandsaw, or something similar.
Step 3: Second Hole Saw Cut
I then go in from the opposite side of the wood, guided by the center hole made by the pilot drill. You will feel a difference in the drill press resistance when you go through. It will sound different, and the torque applied to the wood will relax.
Step 4: Remove Cylinder From Wood
I then take out the cylinder. It should have a flange part way down the side. If you made the roller seal without getting rid of the flange, you would have a depressed line going the length of your final image.
Step 5: Lathework
I chuck it in a lathe, and smooth off the flange with a skew and sandpaper, so I have a smooth sided cylinder. The powered point on the lathe is a special piece that you can get at woodcraft that allows you to center on the middle hole from the holesaw plug.
Step 6: Carving
When you carve an image, remember that everything is in reverse. depressions become high areas, and what was looking left ends up looking right. plan the picture out, and look at it in a mirror, so that you don't end up with backwards N's, or a comparable problem. Notice in the picture that my initials, DP, are facing backwards. I used a dremel with diamond bits to cut the wood. Care has to be taken to make sure that the bit does not catch the wood, and roll away from where you intend to cut. I hold the dremel as close to the bit as possible, and as tight as I can stand for any length of time.
Step 7: Finishing
If you like what you have made, it's time to put a finish on. I normally use Behlen's toy and butcher block finish, although another nontoxic top coat is fine. It will allow you to use the roller seal on food material, such as dough.
Step 8: Waxing
I then polish it with a buffer set, finishing it and waxing it. for that process, After the finish is applied, and dries, I rub the cylinder with steel wool. I then buff it with white diamond polishing compound, then apply wax. Beeswax will work, but Carnauba works better, as it is harder, and will give you a good shine, as well as slick nonstick sides. It is available at woodcraft stores, woodcraft.com and other places as well.
Step 9: Roll a Picture
Test it by rolling it in a strip of Sculpey or some similar material. I wouldn't use Plastilene if it was going to be used to decorate cookies, since Plastilene contains inorganic oil that I am not sure is compatible with food. The sculpey broke when I took it out of the oven. I used a little tape to hold it together so that the image could be seen.