Other than the bottom, I normally don’t measure the thickness of bowls. I just feel with my hands until it’s “about right.” Understandably, beginners have good questions about how thick the sidewalls, endwalls, and bottom should be, so that they have a frame of reference. Having just completed this cherry bowl by my usual hand-and-eye approach to thickness, I took a moment to measure these three areas to see what I ended up with. (By the way, this is the bowl I had started in this post last month.)
There’s room for variation, and what may be “ideal” will differ depending on bowl design, wood species, bowl size, and other factors. This particular bowl is about 19 inches (48cm) long, 12 inches (30.5cm) wide, and just under 5 inches (12.5 cm) high. In the top photo, I’m using double-ended calipers to measure the bottom thickness at the center of the hollow. It measured 5/16″ (8mm).
The calipers I’m using are ones I’ve had around for a while. I think they’re made by Robert Sorby, but there are many different forms around to accomplish the same thing. A search under “double-ended calipers” will yield many possibilities, or a shop-made version could serve well too. What they all have in common is that the gap between the points at one end will equal the gap at the other end. Therefore, thickness can be measured from the back end.
The sidewall thickness as seen in the photo just above is 1/4″ (6mm). The sidewall gets gradually thicker as it descends toward the bottom and also as it rises toward the rim. The width of the rim at its narrowest (halfway along the length of the bowl) is 3/8″ (9.5mm)
The thickness of the endwall as seen above is 1/2″ (12.5mm). The sidewalls can be thinner than the endwalls due to the differences in strength between the long-grain fibers and the end-grain. And endwalls with a shallower slope can be relatively thin compared to those that are more vertical.
For most bowls in general, I’d suggest a bottom thickness of 1/4″–1/2″ (6-12mm), a side wall thickness — at the thinnest point — of 3/16″–3/8″ (3-10mm), and an endwall thickness of 1/2″–3/4″ (12-20mm). I say for most bowls, because there are situations where I might violate those guidelines on purpose. And, since this isn’t a rectangular box made from flat stock, those measurements only provide so much design input. The thicknesses are tapering and blending all over the place. Your eyes and hands will guide you toward the form and feel you’re after, so don’t obsess over numbers.
Here’s a closer shot of the foot of this one — a little design variation. It’s pretty simple to lay out. Draw a couple freehand S curves within the oval, then a C curve for the central vein of each leaf. Trace those lines with some shallow (only about 1/16″ deep) V-tool work, then some strokes with a gouge on the leaf surfaces. I used a #5 8mm for that, but it could be almost anything.
Time to get some oil on it and send it off to its new home.