Segmented ring on solid wood base?

[Roger Wiegand]

I was planning a bowl where I'd use a 2" thick piece of curly maple as a base (bottom of the bowl) and then build up with segmented rings. Will that work? Or will the cross grain movement where the segment piece is perpendicular to the bottom cause it to crack? Never tried anything like this before.

 

[john lucas]

That small you are probably ok. You can look up wood movement charts online and roughly predict how much a 2" piece will move. Not very much unless you subject it to extreme differences in humidity.

 

[Roger Wiegand]

I wasn't clear about my concern, the bowl is going to be about 11" in diameter where the segmented ring joins the solid wood. Using the wood movement chart and a couple of guesses about humidity, the differential shrinkage of the base could be 1/8" to 3/16" tangential vs longitudinal. I'd guess that the segmented ring would be quite stable. That seems like enough to be problematic, but OTOH, I'm pretty sure I've seen a far number of pieces done this way-- or am I misremembering and are bigger segmented bowls always made with segmented rings all the way down?

For myself I'd just try it and see what happens, but I've been asked to make this as a gift and I don't have time to watch it through the seasons.

 

[john lucas]

If you put a solid wood ring on an 11" segmented ring I can almost guarantee it will come loose down the line. I did a few as tests over the years. One was a solid wood platter with an epoxy ring on the outside. I even cut a groove in the outside edge so the epoxy had a place to go. After about 2 years the ring was loose for a couple of inches. Over the next 5 years it more and more of it came loose until I could just pull it off. On another one I made a solid wood ring on the top of a 6" cone shaped segmented vessel. The ring would open up a crack during the winter and then close up during the summer. I made a lot of segmented dog dish shaped bowls early in my career that had solid wood bottoms and segmented sides with segmented contrasting ring on top. I have been able to keep track of a few and all are still together. I do make a lot of hand mirrors that are 5 1/2" wide. There is enough movement in that wood that I leave a counter sunk gap around the glass. The glass of course doesn't move but if I make it fit snug it warps the glass or cracks the wood so I leave a little less than 1/8" all the way around. I have a large segmented bowl that has an outer rim of Cocobolo. The Cocobolo was segmented but was layed out differently than the rings below. I wanted the grain to run differently. I was worried about it both from the standpoint of gluing Cocobolo which is an oily wood, to the maple below, and from the different grain movement. I kept it after the show it was in just to see what happened. Took almost 5 years but it seperated at the Cocobolo glue line. I pays to learn as much as you can about wood movement and take that into consideration when designing pieces.

 

[Roger Wiegand]

Thanks John, you've confirmed my fears about this approach.

 

[hockenbery]

I was planning a bowl where I'd use a 2" thick piece of curly maple as a base (bottom of the bowl) and then build up with segmented rings. Will that work? Or will the cross grain movement where the segment piece is perpendicular to the bottom cause it to crack? Never tried anything like this before.

Generally gluing solid wood to a segment piece will cause problems with the glue joints or cracks in the wood.
Small diameter contact area moves less so you may get away with it.
A segmented base will move with the segmented rings

 

[stu senator]

Of you use a flexible adhesive with a gap of a few thousands of an inch rather then a zero gap with very thin adhesive it should work.

Years ago I had to glue a ceramic and aluminum rings about a meter in diameter for a vacuum joint. I used a .010 gap with flexible epoxy. Small shims held the gap. It worked and held in spite of a heater blasting hot air to warm the building and cool nights.

The adhesive is in shear due to the different expansion of the material on each side of the joint. The thicker glue line reduces the shear stress in the glue to below the maximum failure stress.

Stu

 

[Mike Johnson]

Eclectic E6000 adhesive stays flexible and basically sticks to everything. One of the best adhesives for rough service hard to glue surfaces.

 

[Don Jarvie]

Make the base segmented and drill a 1 to 2 inch hole for a hardwood plug. If you make the base fully segmented, I.e., no plug it will end up splitting on the glue line. The plug won’t expand enough to split the ring since it’s fairly small.

This is how the segmented pros make the bottom.

 

[Roger Wiegand]

When I have time I'll experiment with both the floating base and central plug ideas. The floating base wouldn't work for the bowl I had in mind (the seam will disrupt the shape), but seems a good approach for other shapes. Since I'll be giving the piece away I don't want to risk failure down the road. I'll offer her a more conventional bowl for now and work on learning more about segmentation going forward. Thanks for the suggestions!

 

[egsiegel]

I think it would be safe to say that MOST of the segmented bowls (segmented pieces in general) have a solid piece for the bottom.
I've never had any issue with it just using Titebond in the glue up process.
look at images of segmented pieces. if the ALL failed, I think we would have heard about it by now.

 

[Mike Johnson]

Solid bottom yes, but you need to consider the diameter and the expansion and contraction rate of the solid base versus the segmented rings and the expansion and contraction rate of the wood used in the segmented rings. Most solid bases are a small percentage of the total diameter.

 

[egsiegel]

Solid bottom yes, but you need to consider the diameter and the expansion and contraction rate of the solid base versus the segmented rings and the expansion and contraction rate of the wood used in the segmented rings. Most solid bases are a small percentage of the total diameter.

agreed