Abstract concepts can be difficult to teach. The idea of “riding the bevel,” “rubbing the bevel,” or “floating the bevel” is something which we all learn eventually but to the new woodturner, it can be a very mysterious concept. I have come up with a way to make that better understood by the new woodturner and want to share it with you.
This is a wood cut-out which is about 15″ across and an inch and a half thick. Note the sort of zig-zag features both inside and outside the form. I will hold up my Tom’s Tools bowl gouge against that zag on the outside to show the tool cutting the wood right ahead of where the bevel rides. The bevel, then, is riding right behind the cut. Look at this next picture.
Hold the bowl gouge against that yet-to-be-cut edge with the bevel riding on the wood just cut. That has helped many new turners to see just where the bevel should be. The other seemingly difficult concept which it teaches is having to swing the handle of the gouge to change the direction of the bevel in order to cut a curve. This device can be used to show both outside shaping of a bowl as well as inside hollowing of that bowl. With the bottom of this device shaped as a tenon, it can be helpful to use it when talking about making a tenon, too. But keep reading as I have another great tool for teaching about tenons.
These are five separate pieces which I keep in my classroom box when teaching about the shapes and sizes of tenons. You can see that each of the lighter color pieces actually represents the bottoms of two bowls with the line across the center dividing them. The “bowl” sections are about nine inches across and the “chuck jaws” pieces are about five inches. I painted one side of all pieces a different color so I can use the contrast to better show how they fit together.
This is a good view of the bottom of the bowl and the tenon showing the flat area just outboard of the tenon itself which indexes down on the top edge of the chuck jaws to provide support when hollowing out the inside. The green part in this picture is shaped like the Oneway chuck jaws so the tenon is square.
Here is a different tenon showing the area around the tenon which curves as part of the outside of the bowl so the part which indexes down on the top edge of the jaws is curved, thereby NOT providing support to the bowl when hollowing.
I flipped these over for this picture as they show up better with the lighter side up. These represent three different shapes of chuck jaws, Oneway straight jaws, dovetail jaws, and the sort-of dovetailed jaws of the Nova chuck. My “bowl” pieces have four tenons, one each for each jaw shape and one as above with the curved sides going clear down to the tenon to show how NOT to shape the part which indexes down on the top edge of the jaws.
When you talk to your students about the length of a tenon, these devices are also useful in showing that a tenon should not be so long as to extend clear to the bottom of the inside of the jaws of the chuck.
Feel free to make your own devices like these. That is why I have published pictures with dimensions and an explanation. I have used all of these teaching aids extensively in teaching as well as demos for clubs. I have gotten many positive comments on how much easier it was to understand why tenons are shaped as they are. I am always looking for ways to make the abstract more concrete for my students so if you have methods you have found useful, please share them with me at firstname.lastname@example.org. Thanks.