Bowl Turning Depth Gauge

This bowl turning depth gauge is made from aluminum angle 3/4 inch on a side. It is similar to the box turning depth gauge except that the beam (aluminum angle) is longer. It is helpful to have several of these available so that one that is handy for the work at hand can be used. i.e. not too long and not too short. See the write-up for the box turning gauge for the sizes and materials. On this gauge it is important that there be no knob on the end of the 1/4 inch brass rod.

Note that the gauge has two fixed clamps, one in the center as in the box turning gauge and one at one end. It does not matter which end. The clamp in the center is used like the box gauge to set the inside depth and the thickness of the bottom of the bowl. The clamp at the end is used to set the outside height of the bowl.

To use the gauge, place the beam on the rim of the bowl after having made the top surface flat or very slightly concave. Move the brass rod, with the sliding clamp, over to the fixed clamp at the end. Open the fixed clamp and let the rod slide freely so that it touches the surface that the bowl is sitting on. Then lock the fixed clamp. Next move the sliding clamp to the brass rod that is protruding below the beam i.e. to the side opposite normal and lock the sliding clamp so that it is tight against the bottom of the beam. Release the fixed clamp and move the brass rod back to the center, sliding the brass rod up through the bottom of the beam and through the fixed clamp. Then lock the fixed clamp and remove the sliding clamp. Place the sliding clamp on the normal side of the beam, letting it touch the top of the fixed clamp. Lock the sliding clamp in this position. Now, measure the thickness of the foot and/or chucking spigot; a vernier caliper is useful for this. Unlock the fixed clamp and pull the rod up through the clamp a distance equal to that of the foot just taken. Then lock the fixed clamp again. The length of the projecting brass rod is now equal to the outside height of the bowl minus any foot or chucking spigot. Move the sliding clamp so that it again touches the top of the fixed clamp and lock it in place. Now loosen the fixed clamp and move the rod back a distance equal to the desired thickness of the bottom of the bowl and lock it in that position. The length of the projecting rod is now equal to the desired inside depth of the bowl and the distance between the two clamps, fixed and sliding, is equal to the desired bottom thickness. All of this sounds complicated, but it is very easy after a couple of trials.

Note: Idefinitely do not recommend using these gauges with the lathe running!