Layered Bowls

[rolly1]

I am going to be turning some bowls and want to try layering different woods. Do I need to align the grain in each layer so that expansion and contraction does not end up turning them into scrap?

[cskipper]

good question. I can't wait for someone who knows to tell us the answer.

[SteveColes]

I really know nothing about this. But, it seems to me that grains should be perpindicular to each other like in plywood. I would think that it would the bowel blank much more stable that any solid wood blank

[rolly1]

I found some information but it seems to complicate matters even more. It is not a matter of just grain but how the wood was sawn as well.

Wood has many desirable features that make it the material of choice for many projects, especially furniture-making. Despite the beauty, durability and workability of wood, it does have some disadvantages. One of the most difficult characteristics to manage is called wood movement.
If you were to inspect wood under a microscope, you would discover a structure that resembles a multitude of tiny parallel tubes. When the wood was a part of a tree, these passageways were used to transmit nutrients. Once wood is cut out of a log, these tubes tend to expand and contract in conjunction with temperature and humidity changes.
Wood tends to experience the majority of its expansion and contraction in one particular direction. Wood movement parallel with the grain is negligible, whereas expansion and contraction across the grain is significant.
The rate of expansion and contraction of wood varies from species to species and even from board to board. The amount of movement also seems to decline with age, so an older board may move less than a recently cut one. A general rule of thumb that most woodworkers use is that boards can move up to 1/16" per foot (1mm per 20cm) perpendicular to the grain, and sometimes more.
In small projects the amount of wood movement is often insignificant and can safely be ignored. When larger surfaces are mated, however, wood movement must be taken into consideration. When mounting a large table top to a base, for example, the potential for expansion and contraction can approach 1/2" (13mm). If the woodworker fixedly mounted the top, the wood would crack or bow and the table would be weakened or ruined.
Woodworkers have developed all sorts of techniques to mitigate the problems associated with wood movement. They may use slip joints, oblong holes or special fasteners (such as figure-8 fasteners) to join large boards or panels.
The way in which a particular board was originally cut, also plays a role in the expansion and contraction that it will experience. Quartersawn boards, for example, undergo much less wood movement than their plainsawn counterparts. Alternatively, manufactured panels, such as plywood, particle-board or MDF include so much glue, that expansion and contraction is virtually nonexistent.

[Ken Massingale]

I've layered several 3/4" cutoffs of different species with the grain at random angles from each other for bowls. I haven't had any issues with movement at all. The sizes of the stock for bowls is small so the effect of movement will be minimal. I do as Mike said and apply oils as soon as the turning is completed. Now, all of the scraps I used for this have been in the shop for months and are all at around 10% or less in moisture.
Plus, when I start out to make, say, a 10" bowl or platter, it usually ends up being a 4" model, so the movement issue is further reduced!
ken

[Big Mike]

It is my understanding that as long as you keep the bowls small in the 5" or so range you can orient all the grain in the same direction. I would be concerned about differing movement rates, contraction and expansion if the woods were laminated at right angles to each other. My only basis for thinking this is some reading I have done in segmented bowl books. I would assume some of those rules apply to layered bowls as well. Here is the web site a North Carolina turner, Jim McPhail noted for his wonderful layered bowls.

http://www.jimmcphail.com/

After you do some be sure to post pictures. I have done some in the past but nothing to write home about. I have lots of cutoffs that would make small bowls less than 5" or so. I may be trying some myself again.

[rolly1]

Thank you all for your input.