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Breadboard ends: how much space for wood movement in mortises?

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Forum topic by HTX_woodworker posted 09-04-2018 03:10 AM 1042 views 0 times favorited 7 replies Add to Favorites Watch
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HTX_woodworker

23 posts in 411 days


09-04-2018 03:10 AM

Topic tags/keywords: oak question breadboard ends mortise

I have a 28” wide white oak tabletop I’ll be attaching breadboard ends to for a desk I’m making. The tenons will be 3” wide. I’m trying to determine how much wider the mortises should be.

In this article, the author mentions to leave the mortises in a breadboard end slightly oversized to allow for wood movement:
https://www.woodcraft.com/media/W1siZiIsIjIwMTcvMDgvMjMvMTEvNTkvNTQvMzYzLzUxX0JyZWFkYm9hcmRFbmRzMy5wZGYiXV0/51-BreadboardEnds3.pdf?sha=0262ef8caf95e0b8

However, he didn’t mention roughly how much larger the mortise should be. I’m guessing this is largely dependent on the species used, the moisture content of the wood, and the ambient humidity?

I don’t have a moisture meter, but may have to get one in order to come up with more precise data to help figure this out.

I also plan to be moving to the Saint Louis, Missouri area from the Houston, Texas area. From what I can tell, Houston has 75% average humidity, and Saint Louis has 70% average humidity, but Saint Louis has much dryer winters.

However, this desk would be in a climate-controlled environment at all times. From what I’ve read, the moisture content would still fluctuate, even with air-conditioning.

Any thoughts on how much I should allow for movement within the mortises? I am planning on drawboring each of the tenons, and widening the holes in all but the middle tenon. Cheers!


7 replies so far

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Aj2

2280 posts in 2191 days


#1 posted 09-04-2018 03:21 AM

About a 1/8 inch on each side. Trust me I’m a expert.

-- Aj

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HTX_woodworker

23 posts in 411 days


#2 posted 09-04-2018 06:41 PM

Thank you Aj.

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HTX_woodworker

23 posts in 411 days


#3 posted 09-04-2018 06:45 PM

I’m wondering if an 1/8 inch on each side is necessary, given the current conditions? The desktop is currently in the most humid environment it is likely to be in, as the ambient humidity is around 93% (short of moving to a rainforest, that is!). I was thinking that the tabletop will only shrink at this point. I can definitely understand putting an 1/8 inch on either side of the mortise if I was making this same project in the winter. What are your thoughts?

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newwoodbutcher

794 posts in 3244 days


#4 posted 09-05-2018 12:45 AM

In my opinion, It doesn’t hurt to allow for all the room it potentially needs. I think an 1/8th inch is ok, a 1/4” might be even better

-- Ken

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Robert

3403 posts in 1874 days


#5 posted 09-05-2018 01:15 PM

Sounds about right. Assuming you know you need to elongate the dowel holes too….

-- Everything is a prototype thats why its one of a kind!!

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HTX_woodworker

23 posts in 411 days


#6 posted 09-08-2018 03:06 AM

Yes, I was planning to elongate the dowel holes, as well. Speaking of those, I’ve been debating as to the appropriate diameter: I was considering 3/8”. Any thoughts on this? Should I allow about the same amount of movement (1/8-1/4” on either side) in the dowel slots?


Sounds about right. Assuming you know you need to elongate the dowel holes too….

- rwe2156


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HTX_woodworker

23 posts in 411 days


#7 posted 09-08-2018 03:09 AM

That makes sense. When you say a 1/4”, are you referring to 1/4” on either side of the mortise, or combined (i.e., 1/8” on either side)? Thanks!


In my opinion, It doesn t hurt to allow for all the room it potentially needs. I think an 1/8th inch is ok, a 1/4” might be even better

- newwoodbutcher

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