A jig for planing super thin parts
I make small boxes with sides that are 3/16 in. thick. Preparing stock this thin is a problem, because my planer begins to chew up boards when I try to go under 1/4 in. thick. At best, I get boards that have no tearout but aren’t a consistent thickness. I’m fortunate that there is a drum sander in the shop here at Fine Woodworking, but it’s not always convenienent to use (I live about 35 minutes from work). So, before I made some recent boxes, I sat down to think about how I could mill small pieces of stock to 3/16 in. thick. That’s when I remembered an article by John Reed Fox in FWW #226 that explains how he makes kumiko, a type of Japanese lattice that requires precisely milled thin pieces of stock. He tacks a strip of wood to the sole of his Japanese plane on either side of the blade. These strips are depth stops and allow him to repeatedly plane stock to the same, consistent thickness. I have metal planes, so couldn’t tack anything to them. Instead, I made a planing stop and tacked the thin strips to it. They’re spaced to be just wider than the blade of my No. 4 smoother. There is a guide on each of the strips that keep the plane moving in a straight line. The whole rig clamps into my bench vise and works great. I get beautifully planed stock that’s dead on 3/16 in. thick. Take a look at the photos above to see how it works.
Small planer. The rails of this jig are spaced to be just wider than the blade of a No. 4 smoother. They're just a hair thicker than 3/16 in., so that boards planed with the jig end up 3/16 in. thick. A cleat is clamped in a vise to hold the jig still during use.
Drop in the stock. It's best to start with boards that are just barely thicker than 3/16 in. I make them at the bandsaw, cutting them around 7/32 in. thick. One face should already be jointed and planed clean, because if you plane it after using the jig, the board is no longer the desired thickness.
Plane away. The guides not only keep the plane moving straight ahead, but also prevent it from swerving off course and cutting into the rails. Just keep planing until you no longer get any shavings. The board is now a consistent thickness.
Clean, smooth, and ready for work. One of the benefits of hand planing thin stock this way is that when you're done the boards are pretty much ready for a finish. After I've made a box with stock prepared in the jig, all it needs is a light sanding before I apply the first coat of shellac.