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Breadboard tenon length on large breadboards

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Forum topic by AJacob posted 12-26-2017 02:20 PM 448 views 0 times favorited 2 replies Add to Favorites Watch
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AJacob

1 post in 233 days


12-26-2017 02:20 PM

I’m building a table with breadboards that 38” long X 1 1/2 thick X 10” wide. The wood is douglas fir. How long should I make my tenons. I’ve read the length of tenon is at least 5x the thickness of the tenon. Tenon is 1/3 the thickness of the wood, so the tenon will be 1/2 inch, making the tenon 2 1/2 inches long at least. That seems to short for 10” wide breadboar. How long would you all recommend?


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JBrow

1366 posts in 999 days


#1 posted 12-31-2017 03:00 AM

AJacob,

I am a long way from being an expert on breadboards so I am not sure why the rule of thumb you cited exists. Absent this understanding, I agree that a 2-1/2” long tenon seems short for a 10” wide breadboard. But if the breadboard remains flat over time, 2-1/2” long tenons may be sufficient. My only concern is that tenons too short might cause the breadboard connection to fail should someone sit on the breadboard. I cannot say whether this is a real or imaginary concern.

The only problems I can foresee with longer tenons is chopping well-fitting deep mortises would be more difficult. Also a 10” wide board with long tenons that are pinned too far away from the table top/breadboard joint could cause the breadboard to crack. If pinned close to the table top/breadboard joint, then the breadboard could still expand and contract.

I assume there is a good reason for such a wide breadboard. If reducing its width is not practical, then ensuring the breadboard is quartersawn could at least reduce or eliminate cupping of the wide breadboard. I doubt that longer tenons could resist the forces associated with a cupping breadboard.

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pintodeluxe

5732 posts in 2893 days


#2 posted 12-31-2017 05:29 AM

10” breadboards are too wide. Other than aesthetics, there is no reason for a breadboard wider than 3-1/2” – 4”.
In the case of these standard dimension breadboards, the tenons can be about 2-1/2” long.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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