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Spill Planes

By Herb Kean
Originally published in The Tool Shed, Number 127 (June 2003)
How many of you have bought a spill plane and tried to make spills? The odds are that you won't get a really good spill on the as-found plane. What's worse is that from time to time on a plane that originally produced good spills, you end up with lousy ones. Many articles, and also a chapter in a book, have been written about this phenomenon, and I have tuned up spill planes just before a demonstration, but neither the articles, the book, nor I, have found all the secrets that takes it out of the luck category. A couple of obvious things like sharpening the blade, tightening the wedge etc. do not always solve the problem.

When my son Steve asked me to make him a spill plane to show it off to his customers, I told him that I would rather buy one and fumble around trying to get it to work. Making one from scratch looked to be more time consuming. However, I told him I would make one and record the time.

My philosophy has always been, "You learn by doing." I felt most definitely that I would uncover some of the secrets of these planes that up to that time escaped me. I laid out the sketch for the easiest spill plane that I knew of: the two piece model (improved to a three piece model later). I also picked the blade orientation as "flat" to simplify the mortise work. See Figure 1 for the finished plane. Making the plane was relatively easy, and I surprised myself with how little time I spent completing the basics. But, as suspected, it didn't work nearly well enough to suit me.

Figure 1
Figure 1. Author's home made spill plane.

Then came the learning part. I separated out every conceivable variable that existed, and worked on them one by one. As improbable as it appeared, there were fifteen variables that affected the production of a "perfect" spill. See Figure 7 for a tightly-wound, tapered and stiff "perfect" spill. I will list them at the end of the article so as not to muddy up your reading with technical jargon. If you really want to make, or tune up, a spill plane, you can battle through the fifteen points at the end.

Figure 2
Figure 2. Two-piece spill plane with flat blade and a half-eye escapement.

After getting my newly made plane to cut great spills, I decided to put the variables to the test. If they were truly meaningful, I should be able to get all five of my other spill planes to work. At the time, two of them worked intermittently, one worked fine, and two didn't work worth a tinker's dam. It took the better part of a morning to apply most of the variables to all those planes. However, I'm happy to say that they now all work. And, the thing that I really feel great about is the fact that the mystery is gone. Almost any configuration plane at a sharply skewed angle works if tuned with the variables! And rightly so, as the people making these planes were rarely professional planemakers and I suspect that very few knew anything about critical compound angles etc. When you follow the rules, you too, with very little concern for accuracy, can make or tune a spill plane.

Figure 3
Figure 3. Molding plane body spill plane.
Six different styles (and there are others) are shown in the photos: Figure 1. (above) Three-piece with a "flat" blade and a full-eye escapement; Figure 2. (above) Two-piece with a "flat" blade and a half-eye escapement; Figure 3. (above) Molding plane body with a horizontal sole and a wedged escapement (most of these are actually modified from an existing molding plane); Figure 4. V-bottom sole with a half-eye escapement; Figure 5. Double-fenced sole with a parallel escapement; Figure 6. Double-fenced sole with a half-eye escapement. There are as many more types as there are creative woodworkers.
Figure 4
Figure 4. Spill plane with a V-bottom sole and half-eye escapement.
Figure 5
Figure 5. Double-fenced spill plane with a parallel escapement.
Figure 6
Figure 6. Double-fenced spill plane with a half-eye escapement.
Here are the variables, in no particular order:
  1. A razor sharp blade.
  2. A super tight wedge.
  3. The lower tip of the wedge cannot interfere with the escapement. In many cases it is contoured in a cove to match the rest of the escapement. Over time, dimensional changes may create this interference.
  4. The grain orientation of the work piece should be such that you are not planing grain running up toward you. Even parallel grain is not as good as grain running up away from you. (Opposite for bench models where the plane is upside down.)
  5. A wider board works better with the models that are held in a vise or clamped to the bench. Straight-grained pine works best.
  6. Double-fenced soles that capture the work piece allow for a more consistent shaving thickness, and easier planing.
  7. It is easier to push, and to curl the shaving when the exposure of the blade is minimal.
  8. The angle of the edge of the blade to the forward edge of the mouth can be adjusted in the "flat" blade models so as to get a tighter spill.
  9. The space between the edge of the blade and the forward edge of the mouth can be adjusted in the "flat" blade models so as to get a tighter spill.
  10. The inside of the fence should be square to the sole.
  11. The blade edge must be dead parallel to the sole to prevent cumulative tiny angle errors from beveling the workpiece.
  12. The workpiece should start from a true jointed edge. If you are going to make a lot of these spills, it's not a bad idea to square up the edge of the workpiece now and then when it starts going out of square, or not yielding a good spill.
  13. Sometimes a slower stroke with downward pressure helps to true up the edge for subsequent strokes. Usually the stroke is rapid.
  14. It might take 3 or 4 passes to get the plane and the workpiece to "find each other", before a good spill emerges.
  15. If the spill breaks up before its full length, check to see that the rear portion of the sole is not vertically lower than the forward portion. If it is -- get the soles to match. A sole that starts off dead flat in both sections can sometimes change over the length of a heating season.
 Tightly-curled spill
Figure 7. Tightly-curled spill ready to light a pipe or candle around the house.
If you really work at trying to understand what makes a spill plane function, almost any configuration will provide you with a decent spill. And a simple but gutsy model like Figure 1, will give you perfect spills for as long as your arms can keep moving.
Afterthought: When Doris proofread this article, her only comment was: "How can anyone get so wound up over a little wooden shaving?" (Opposites definitely attract.)