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Adventures in side bending
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Author:  J De Rocher [ Thu Feb 04, 2021 9:05 pm ]
Post subject:  Adventures in side bending
I just finished bending a set of birds eye maple sides and the wood did something interesting I haven't seen before. I bent the first side and a section about 4" long between the tip of the lower bout and the tail cupped outwards by a lot. By about twice the thickness of the side. However, both edges of the side through that area fit right onto the body plan outline. So the wood had swelled outward in the middle of the side to form a blister shape. The rest of each side bent nice and flat so it was something specific to that area of the wood.

I went ahead and bent the other side and it did the exact same thing in the same location. I previously fixed side cupping on another set of sides by installing a side brace that flattened the side nicely, but the cupping in that case was only about 1/2 the thickness of the sides. This cupping was much worse.

I left the sides on the bench to consider whether to scrap them or to go ahead and use them and hope that hefty side braces would be enough to take out the cupping. When I came back in the morning, the cupping on both sides had flattened out completely. Weird. It's not like I had soaked the wood with water before bending. I only spritz lightly with water and only on the inside of the bends and not on the outside of the bends. Also, I bend the wood directly against the hot pipe so the water gets driven off pretty fast. The fact that the cupping happened in the same location on the two bookmatched pieces says that the wood in that location is different in some way from the rest of the side, but there's nothing obviously different in its appearance.

Anyway, I thought I would post this in case anyone runs into something similar. It may self correct given some time. Since the wood is wonky in those spots, I'm going to install side braces there to make sure the sides stay flat.

Separately, the birds eyes made bending these sides more of a challenge than most. The birds eyes are much less flexible than the rest of the wood so they introduce rigid spots which make the wood want to bend in facets.

Attachment:
Side cupping after bending 1.jpg

Attachment:
Side cupping after bending 2.jpg
Author:  phavriluk [ Fri Feb 05, 2021 12:24 am ]
Post subject:  Re: Adventures in side bending
That must have been quite a surprise! There's something to be said about sleeping on a problem.
Author:  George L [ Fri Feb 05, 2021 12:24 am ]
Post subject:  Re: Adventures in side bending
That is weird. All's well that ends well, I guess. Hopefully things will stay put for you from here forward. I'm about to bend some figured maple (not birds eye) and am somewhat leery about it. I've only worked with maple a couple of times before, but it always seems to do things that I've not encountered with other woods. It's beautiful but mysterious.

I was at a lumber yard recently, picking through some maple trim and found one oddball 8' stick with heavy birds eye. Wouldn't match the rest of the pieces but I bought it anyway because it was too lovely to pass up. Just yesterday I realized it would be perfect for framing an art piece I bought my wife for our anniversary.

Ain't wood grand?
Author:  J De Rocher [ Fri Feb 05, 2021 12:55 am ]
Post subject:  Re: Adventures in side bending
phavriluk wrote:
That must have been quite a surprise! There's something to be said about sleeping on a problem.


Words to live by, and build by in my experience. Sleeping on it has given me the answers to a bunch of problems.
Author:  J De Rocher [ Fri Feb 05, 2021 12:58 am ]
Post subject:  Re: Adventures in side bending
George L wrote:
That is weird. All's well that ends well, I guess. ?


All's well that bends well. Sorry, couldn't resist.
Author:  Clay S. [ Fri Feb 05, 2021 9:18 pm ]
Post subject:  Re: Adventures in side bending
Birdseye maple is flatsawn. If it wasn't it wouldn't show the birdseye figure. That might account for some of the cupping from bending - more moisture on one side of the side than the other.
Author:  J De Rocher [ Fri Feb 05, 2021 10:48 pm ]
Post subject:  Re: Adventures in side bending
Clay S. wrote:
Birdseye maple is flatsawn. If it wasn't it wouldn't show the birdseye figure. That might account for some of the cupping from bending - more moisture on one side of the side than the other.


Thanks for that, Clay. I wasn't aware that that was how the birds eyes are made visible.

It's interesting that it happened only at the same corresponding location on both sides, but nowhere else on either side. And the cupping was in the lower bout between the tip of the bout and the tail which is a pretty mild bend so less water was spritzed there than at the waist or upper bout bends. And the water was only applied to the inside surface of the bend so it seems that, if anything, the cupping should have been inward. Maybe some of the water got through the wood to the outside surface. The maple is also curly so there would presumably be some end grain exposed that water might travel through. Contact with the hot pipe would have quickly driven off the water on the inside surface, but maybe any water that soaked through might have remained and caused the outside surface to swell outward. The grain lines are slightly farther apart in that area so maybe more flatsawn and more susceptible?
Author:  doncaparker [ Sat Feb 06, 2021 7:25 am ]
Post subject:  Re: Adventures in side bending
I have had this happen too, and it was with maple sides that had some figure. It has made me wary of interesting looking maple. I prefer sides that behave over sides that are pretty, if I can’t have both.
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