how to construct an arc from joined straight segments

[Jodi]

I am building a headboard that requires an arched border along the top edge. The border is 3 1/2 inches tall (the side that faces outward) and 1 1/2 inches thick (top edge). So it's not the type of arc that can be bent.

My plan was to piece 5 wide straight segments together with angled joints then cut the arc from this. The segments would be 22" long for the center and 2 14" segments on each side. I started worrying, however about the integrity of the joints. First, they would be end grain to end grain - I could do a lap joint or a dado to help with that (I don't think biscuits would be enough). Second, I was worried about the wood movement. As the segments swelled, on the convex side of the arc the joints would grow apart, and on the concave side they would push toward each other. I thought this might make the joint break.

Does anyone have experience with something like this? Is there any other way to do it? Should I have smaller segments between joints? Is there enough movement in 3 1/2 inches to cause any problems?

This is my first commissioned piece for someone else, so I really want to get it right.

Thanks for any advice you can give.

Jodi

[David Hall]

If it were me I would do it pretty much as you are planning. I would lay out the boards, rough draw the arch and then attach the boards together with dowels or mortises and loose tenons making damn sure that they are well within the arch area so that they do not get cut into when cutting out the arch. Is there any way do incorporate a design pattern at the joints so they look like they were desired, not just necessary? The other option, as I see it, would result in significant waste, but I think I saw in an another post that the arch is either 6" or 9". You could glue up a panel large enough to accomodate the arch and just cut it out. This would look best in my opinion. I don't know if there are other aspects of the headboard that could be made out of the scrap that would result or if there is room in the commission budget to waste this much wood.

Dave Hall

[Steve]

Jodi,

You might consider "brick-laid" construction. Use 1/2 inch thick pieces the same height and width that you are considering, (but approx. 3x as many). You get long-grain to long-grain glue joints. A garden arch I built with this method has lasted several years with no apparent separation.

Steve Stripl>I am building a headboard that requires an arched border along the top

[Glenn Cramond]

Would this bit be useful?

[Dr. Rev. Chuck, M.D. P.A.]

It's one of the two preferred methods for constructing banjo shells, which must withstand a lifetime of tension without failure.