When/how do you "stitch" a split with a dovetail

[NormCloutier]

I recently rough-turned a 19" platter from a lovely crotch piece of 150-yr-old pecan. I knew the risk when I started, but the crotch seam has of course started to split as the piece is drying. It's not a typical cracking split, but there is a growing gap.

The figure is lovely so I am hoping to "stitch" the piece with a wedge of contrasting wood in a dovetail configuration, as I have seen done.

But when do I do that, and can anyone help me understand how best to approach it?

In other words, do I let the piece continue to dry as is and then work on adding the bow-tie just before final turning? Or do I try to add the piece now to reduce further shifting?

I assume the work involves drilling and using hand chisels or a scroll saw to cut out the shape and then make a tie to fit it. But I'm just guessing and hoping some of the experts here can provide or point me to some guidance.

The attached photo shows the piece after rough turning, the dark line has become more of a split since then. I do plan on filling some of the void with epoxy as well.

-- WeekendTurner

 

[Bill Boehme]

I think that what you are looking for is called a Dutchman. It would only be cosmetic, but it is fairly simple. Make the bow-tie, sit it in place and make an outline with a sharp pencil or scribe. Drill and chisel to the depth that you desire, but not more than the thickness of the bow-tie. Glue and turn flush. There are other fixes that are interesting such as metal rods like brass and aluminum or copper wire laced up like a shoe or even leather lacing or real shoe laces. Be very careful turning that thing. People have been seriously injured from things exactly like what you are turning when the split and fly off the lathe.

 

[MichaelMouse]

Actually, it's a Japanese (Nakashima), not a Dutchman, Bill. The Dutchman is less than full depth, and is intended to cover a surface defect that looks worse than the Dutchman. Here's a Nakashima. http://www.galere.net/pics/prodimg-417.jpg

May I assume it's the bark inclusion area? If so, should you try to insert one now, you're likely to hold the middle while the ends open. I'd wait, unless you're going to do two or three. Then, I'd put up a little three-legged plywood platform big enough to stabilize my router base while I routed the opening(s) with a nice up spiral bit. You can do by hand, if you like. Score, bore, pare.

Glue your patch in firmly, long grain across the gap, turn carefully. I'm sure you know that (radial) speed kills, so keep it down as you re-flatten, and keep your ears peeled for a click that sounds out of normal. Stop and inspect to see if the crack is growing, though I would not expect it to. Maybe some of the reaction wood might pop.

 

[NormCloutier]

Actually, it's a Japanese (Nakashima), not a Dutchman, Bill. The Dutchman is less than full depth, and is intended to cover a surface defect that looks worse than the Dutchman...

Thanks Michael. The term "Nakishima" led me to the artist and ultimately, the name of what I was trying to find: Butterfly joint.

From Wikipedia, the free encyclopedia

A Butterfly joint is a type of joint used either to hold two or more wooden boards together or to keep two halves of a board that have already started to split from splitting further. They may also be used to stabilize the core of a knothole, preventing it from dropping out over time.

A butterfly joint resembles two dovetails connected at the narrow part. A negative of the hole is cut out of the board the butterfly will be placed in and the butterfly is then fitted, keeping the joint together. The wood used for the butterfly is usually a contrasting wood, often walnut.

Butterfly joints are common in the work of George Nakashima. They were also used in repairing cracks in tabletops in the 18th century. The "butterfly" was installed across the crack to stabilize and inhibit further movement of the crack.
​

I think I will wait as you suggest, but will probably go with two of them depending on how it dries. Speed will be high in my mind only, and a full head-shield will certainly be employed.

 

[Bill Boehme]

OK, a Dutchman on steroids. 🙂

Watch where you stand while turning it. Wear your headgear, but keep in mind that there is not any piece of headgear around that can protect you if you get hit by half of that bowl.

 

[hockenbery]

Jerry Kermode has a technique that is simple, effective, and attractive.
uses a stitch method with biscuits. He has demoed this many places and has an article in an AAW journal 14.2 p 28.

He cuts across the opening with a biscuit joiner. Cuts biscuits from contrasting woods and glues them in.
Then turns the bowl.

One issue with a butterfly joint is that it becomes prominent feature. It may fight visually with the crotch grain.

Be careful! Be safe!
Al

 

[john lucas]

My friend who chainsaw carves large sculptures out of green wood put the butterfly patches in while still green. It keeps the wood from splitting worse. He did a 36' sculpture for the local hospital out of a large log and had about 40 of them in it. The figures are about 12 feet tall. I went by the other day to look at it with a friend and it's as good as it was on day one. It's been in the west window of the hospital atrium for about 5 years now.
http://bradsells.com/?page_id=73

I do them just like Bill said. Make the butterfly patch. Mark it on the wood. Drill and use a Dremel to get rid of most of the waste and then chisel very accurately by hand up to the scribed line. If you have some white chalk rub it into the scribed line before you start. Helps define the line so you can see it.

 

[KellyDunn]

Norm, I have done many hundreds of them. Its traditional here in hawaii. If you just want to do a few hand cut them in. You can all the way or only about 1/8th inch deep. I only do 1/8th these days. I use a router jig made for doing this. You can use med thick ca or epoxy. A straight grain butterfly will hold very well a crack. They are not just cosmetic. They work. They also add value to work. Here they call them Pewa. Hawaiian for fishtail.