Table breadboard/endcap design

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  #1  
Old 03-03-17, 10:47 AM
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Table breadboard/endcap design

I hear pinned mortise and tennon is the best way of attaching breadboard ends to tables mostly because of wood movement in the different grain orientations (~8% tangenatal ~0% longitudinal)

First question: is this such a problem after wood is finished? Does sufficient coats of any kind of varnish create enough of a moisure seal to prevent such drastic movement

If not my second question is if wood moves this much then there wood be a drastic difference in the edge b/w breadboard and table top, are noticeable misalignments seen throughout the year with pinned mortise and tennon breadboards?

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  #2  
Old 03-03-17, 12:57 PM
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It's not so much a question of movement but rather it being a weak point. Dowels or biscuits will give the breadboard more support. Usually there isn't enough moisture involved for that to be a big issue.
 
  #3  
Old 03-03-17, 03:26 PM
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I've built a number of tables with BB ends. Pinned M/T is a good way to go; or you can glue it on only in the center, allowing it to move from center out in both direction. I think the pins are more secure, as long as the holes in the tenons for the pins near the edge of the table are oversized to allow for movement. The pins will be tight in the BB end, but loose in the tenon, if that's clear.

Assuming the wood is properly dried before construction you will still see movement from changes in humidity, and to a lesser extent, temperature. For a piece in conditioned air year round it's not much of a problem. But a piece that sees 20 % RH in the winter and 70% in the summer will move quite a bit.

Multiple coats of a film forming finish, such as varnish or lacquer will slow down the movement with humidity, but typically won't stop it entirely. Oil finishes like BLO or Danish oil aren't as effective at slowing movement with humidity.

Assuming the BB ends are the same species and thickness of wood, you won't see much difference in the thickness of the boards, so you won't see a lip between the BB end and the table top. You will see and feel a difference at the ends of the BB end in relation to the sides of the table top as the top gets wider with humidity.

Here's a link to a calculator that lets you estimate wood movement so you can see what to expect:

Woodworkers Source: Estimate Wood Movement [custom wws]
 
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