Am most of you know, the majority of my turning is segmented bowl/enclosed forms.
Like all good turners, I endevor to make the walls of the stuff I turn, a good uniform thickness. One of the reasons that we do that with solid wood turning, is so that wood movement, due to environmental changes will be uniform, lessening internal stresses, and reducing the likelyhood of cracking.
Question: does the same apply to segmented work? Yes, all wood moves, but in segmented turning there are different factors - (most) all of the wood is oriented the same direction, glue joints, etc.
The reason that I ask, On the hollow form vases that I make with small bottoms, I would love to start fairly thin on the top, and go thicker towards the bottom to lower the center of gravity and make them more stable. I know in practice, I could make the walls all uniform, and just put a baggie of sand in the bottom, but I would rather not.
>This won't answer your question, but it is a discussion on wall thickness and uniformity as I see them.
Thick, thin, thicker and thinner are relative terms that mean different things to different people. I have never destroyed a bowl to test the strength of the glue joints, however there are a few observations that I can share.
When an end-glued segmented ring is used as the rim on a plate, wood movement in either solid wood or an assembly will break an occasional joint in the rim when it is 1/16" thick, but the joints in a rim that is 1/8" thick have never broken.
An end-graion joint in a rim with a curved section is stronger than one that is relatively flat, regardless of its thickness.
The joints in a bowl are different because all of them are captured between flat-grain, except at the rim. Because the joints are "open" at the rim, some curvature and a little extra thickness may be appropriate in that area of the bowl.
The only time I have had problems with the interior joints down in the bowl was when I was still using solid wood for the bottoms. I have had no problems since I started using a segmented bottom. I attribute that to the wood movement being more uniform in the segmented bottom.
Uniform wall thickness is also a subjective concept. How uniform is uniform?? It is fact of life that the curvature on the inside will be different from that of the outside unless we want to make a "footless" bowl, or one whose inside is flat on the bottom to match the flat base on the outside. Maintaining a smooth curve on the inside of the bowl will dictate that it is thicker near the bottom; and that has nothing to do with it being a segmented or solid wood bowl.
I could argue the case that a uniform thickness is needed in a segmented bowl for the same reasons that they are used in a solid wood bowl. Thick wood moves more than thin wood, and the stresses are higher in the thicker wood. However, I have made segmented and solid wood bowls with thicker bottoms and there have been no problems with either of them after the wood has dried in the solid wood bowl.
I think the rules for a smooth and flowing fair curve is as important for the inside of the bowl as for the outside; but there is no "Rule" that says to be a perfect match with the outside curveature.
Several years ago I made a series of spherical bowls, first in solid wood, and then some that were made from segment rings. The inside was also as close to being spherical as I could get it, but offset to provide a thick bottom so the bowl would always roll back to the preferred position. There were no problems with wood movement.
As to the wall thickness in a segmented bowl, thickness is a perception of the viewer. Some folks like thick bowls, while others perfer them them thinner and lighter. Those who prefer a thick bowl want to use it, those who prefer a thin bowl want to look at it. That is the same with either segmented or solid wood bowls.
A tightly fitted glue joint is a strong glue joint, and a loose joint with a gap that is filled with glue is a weak joint, regardless of their wall thickness. I have made 10" bowls that were 3/8" thickness and 18" bowl;s that were 3/16" thickness, and I have made a couple 10" bowls that were less than 1/8" thick just to prove that I could do it. None of them had any problems with movement in the joints.
There is comfort-zone for the wall thickness in a segmented assembly, and that will be different for different people. There are some practical limits, but I have found that segemnted bowls are no different from those made from solid wood. Their wall thickness gets thinner and more uniform, automatically, the more of them we make.
Having said all of that, I look at 3/16" as a practical thickness limit for a segmented bowl. Any thinner than that, and folks will start asking questions about its strength. I have lost a sale as soon as they start asking those questions.
>Thanks for the well thought out response Russ. I'm going to have to print it and re-read it a couple of times to take it all in. I agree with 3/16 as a minimum. For awhile I was going thinner, but customer feedback was that they wanted a more solid feel. (I think us turners are the only ones hung up on super thin walls). I think that there is a "right" feel to every piece and some need thinner walls than others.
>If we are going to keep everything we make, we can turn the walls to any thickness (or thinness) that we want.
If we are selling bowls, we have to listen to the customers. The integrity of the bowl and the joints should never be a concern for the potential buyer. If they are asking questions about it, the bowls are too thin, and we are losing sales.
>Mark, I think a piece can be too heavy or too light, rather than too thick or too thin. To me the weight of a piece is more important than the thickness of it. For example, a hard maple bowl should be thinner than a soft maple bowl.
>Hi there I agree to make the walls of pieces thick up to a point for bowls 1/2" my bowls if they fall they do not break also my vases I have seen in a show here in the open air pieces fly away with a gust of wind due to ligness and hundreds of hard earn dollars go to the floor in pieces if you go to creft fairs or other places do not let the pieces be handled if they are delicate queep the show and wow pieces behind a glass or suffer thinness is for show not sales of utility items period.
