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Reply by uffitze

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Posted on Needs tips for making/inserting structural butterfly keys

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uffitze

199 posts in 1612 days


#1 posted 08-25-2010 08:17 PM

1. Will adding a key to stop this crack simply mean another crack will start elsewhere?
Yep. As wood dries it shrinks across the growth rings, so the outer edges of the wood are going to shrink more than the heart, and you are going to get cracks.

2. Is there a right or wrong time to add the key? I assume the sooner the better.
Given (1), I would wait until the thing is dry. But, if you want to limit the size of any one crack, then you could throw one in at any time.

3. The cookie in question is 2.5” to 3” thick, and has a diameter ranging from 39” to 49” (thus a circumference of about 140”), so even 2% shrinkage could result in over 2” of gaps in cracks —how thick should the key be to provide the necessary support for that much wood/force? I’ve seen decorative butterflies discussed that are 1/8” to 3/16” thick. I can’t image that would be enough to hold this piece of wood. I’ve some posts talk about 1” deep mortises. And do I need butterlfies on top and bottom?
I’d probably use one that is a bit beefier than 1/8” ... 3/4” or 1” would probably hold fine, but if the crack is big enough, you might want one that is full thickness just for aesthetic reasons.

4. The whole cookie is end grain—I assume the key should have the grain running the length of the key, so that the forces pulling it appart will be pulling on the strong, long grain.
Yep.


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