breadboard ends( battling movement)

Furniture making techniques with solid wood.
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RLSIII
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breadboard ends( battling movement)

Sun Jan 18, 2015 9:57 am

ive been finishing a small table recently and as i begin work on the top i have been tempted to complicate things by attempting a breadboard end with mitered returns. mulling this over as i drew, it occurred to me that this would seem to violate the laws of wood movement. as the table top slab moves across the grain it would seem that the miters would open up seasonally. I recall a mitered breadboard end on the Ming inspiration table I was drooling over a while back and wondered what everyones thoughts were on the most logical way to join the two pieces accounting for this conflict of grain direction. I seem to recall several tenons with a "tongue" that continued up the miters and corresponding mortises/dado on the breadboard end.
my apologies if this was covered previously I did not go back through all the archived posts to see if it was mentioned.
any insight in much appreciated

thanks
Rob S
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Brian
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Re: breadboard ends( battling movement)

Sun Jan 18, 2015 10:48 am

It works on that table because the top is split in two halves. The two halves are fitted into a groove in the center support and then fixed on the ends, all of the wood movement expands inward toward the center support and the tongue and groove assembly accounts for that movement.

A single solid slab of wood with mitered ends on the breadboard will not work out in the same fashion.
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Chris Hall
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Re: breadboard ends( battling movement)

Sun Jan 18, 2015 11:14 am

A question worthy of much discussion I feel. I would say - my opinion here- that the purpose of the breadboard end primarily is to cover the end grain and dampen moisture exchange at the table end. The idea that a breadboard end, at least if it is the same thickness as the table top, will stiffen the top against movement (cupping) is probably wildly optimistic.

Also a note: the 'Ming Inspiration' table did NOT have breadboard ends as it was not constructed with a table top slab but with a unique type of frame and panel construction. The frame and panel in most respects is simulating the look of a slab top with mitered breadboard ends on that table. Brian's observation about how that table design accommodates movement is correct.

I built a table many years back which had a bubinga plank top about 30" wide with mitered breadboard ends. It seems to have worked okay over time, however it spends its time in an environment with a narrower seasonal swing in relative humidity than other places.

I think that the use of mitered breadboard ends is a more workable proposition given these conditions:

-placement in an area with narrower seasonal RH swing
-using a table top wood with a quartersawn orientation generally
-using a wood species for the top which doesn't move much seasonally

You need to be able to calculate the amount of movement to expect, given the species, moisture content, grain orientation, and RH range in the environment in which the piece will be placed. You need this information in hand at the design phase. The top will move, and there inevitably will be times of the year that the miter is slightly open or cranked up tight.

Of course the attachment of top to the breadboard ends must allow for the top to move relative to the ends. Assuming you follow the standard strategies in that regard (tenon pinned in the middle, and tenons toward the outside with elongated pin slots), one thing that will tend to happen at the mitered interface is that table shrinkage will tend to push the mitered end of the breadboard away, bending the breadboard ends. Of course a gap would open up at the miter, however this is preferable to a crack being propagated on the tabletop. Still, that crack remains a risk.
" I seem to recall several tenons with a "tongue" that continued up the miters and corresponding mortises/dado on the breadboard end. "
The purpose of the tongue/groove at the miters is to keep the upper and lower surfaces of the pieces more closely registered to one another. Without the tongue, there would be room for the mitered portion of either the table top or the breadboard end to warp or cup slightly, leaving a non-smooth interface between the parts along the miter.

I've thought about this issue a great deal. Initially I designed the coffee table (detailed in the 'Square Deal' series of blog posts) with mitered breadboard ends, then, realizing it wouldn't work so well, went to an arrangement of having a miter at only one end of the breadboard at each side (pinned at the miter and floating everywhere else it was connected), then moved to the idea of the hammerhead keys, which I feel is closer to an 'optimal' solution. The table will be in an environment with modest seasonal RH swing, but the top has a significant portion of tangential grain, which will means a possible 1/4" of movement in the wood used for the top (bubinga). I was apprehensive about the performance of mitered breadboard ends in this context and avoided it.

Really, the time-tested classic solution, if you want to control movement and have the parts well fitting at the miters, is to move to a mitered frame and floating panel arrangement. The trade off, of course, is a table surface with crud-catching grooves along the panel edge and a less seamless visual than you would get with a one-piece top. If the top is to be constructed from a glue up of boards however, then I'm not sure if it is any 'quieter' looking than the frame and panel with a one piece or two-piece (etc.) panel.

Balance that form of construction and its drawbacks/advantages off against the offsets that will happen at different times of the year with a breadboard end relative to the slab.

With the 'Square Deal' coffee table, I had the unique opportunity of using a single 38" wide bubinga slab, and it was a technical challenge for me to solve the 'breadboard' issue. When I experienced the top cupping at various junctures during the build, and was getting quite nervous about it at some stages, losing sleep and all, I started to wonder if it might not have been better to have gone to frame and panel. A panel can have thick dovetail battens fitted to the underside which will definitely keep it flat. I controlled that top and kept it flat with clamps and weights, but it was quite nerve-wracking at times, believe me.

Looking at Ming tables generally, a slab top seems to have been confined to use on tables which were relatively narrow - in fact, it was highly desired to have a thick slab top on such tables, though the weight of that top posed a challenge for 3-way mitered connections at the table corners. Few of those tables have survived - a fine example is at the Minneapolis Institute of Arts. These narrow tables often had everted flange ends, which were also mitered at the top's end sides, but I think the narrowness of the table tops in those pieces makes this construction a more viable proposition. Any wider Ming tables I have seen, like painting tables, are always made with frame and panel construction. It is possible that some were made with slabs, but none of those have survived.

Looking at tables in museums from the 1700~1900 period, a very common thing to see on any table with slab tops or slab folding leaves, etc., is warpage and cupping. It tends to suggest that it is not a method of construction which keeps strictly flat over time.

So, I guess I tend to feel that the frame and panel approach is the most ideal, while being clear on the drawbacks. You can make a slab top work in various way, but drawbacks also abound.
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Re: breadboard ends( battling movement)

Sun Jan 18, 2015 12:10 pm

With a mitered frame and panel design... the panel could be overlain/raised (correct term?) to eliminate the groove that would catch crude. Kinda like the tops on toolchests:

Image

(I guess this is my delurking post, hi everyone!)
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Timateo
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Re: breadboard ends( battling movement)

Sun Jan 18, 2015 12:24 pm

An interesting subject well worthy of discussion.If i live and build suited to my region and climate would my methods and approach change or be slightly adjusted if that region and climate were to change? I had recently seen an old japanese carpenter talk about working with nature or against it. At one point he was talking about these large maybe 8' tall shoji screens he had built. He began talking about how the vertical runs were placed the same way that they were growing and in doing this they wouldn't warp?is it possible to look at a pre milled board and know which way it was growing? I beleive he milled most of his stock from slabs so i can see it being easier to identify at that point. Should the movement of wood and orientation of the parts be more carefully thought out? What about the use of different woods in the same piece but each reacting differently to the fluctuation in the environment?
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Timateo
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Re: breadboard ends( battling movement)

Sun Jan 18, 2015 1:11 pm

And does the season in which you build have an effect on the approach you would use? More tolerance for movement?ect...?The floating panel is obviously a way to allow for that movement. So the next question.would an openened miter be a little much for a high end piece of furniture? I would assume the more drastic the climate fluctuation the more drastic the movement in the piece. I live in tennessee where the humidity rises and drops considerably. I moved out here from seattle and this exact topic has been on my mind due to the effect it has on the overall character and finish of the piece.just food for thought if anyone cares to bite.
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RLSIII
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Re: breadboard ends( battling movement)

Sun Jan 18, 2015 9:59 pm

I forgot about the central divider on that piece, focused on the expansion problem. genius solution. as I will be using a single slab of rift sawn black walnut approx 20"x 32"x2" and spaulted maple breadboard end. I feel a more traditional breadboard would suffice. though the idea of a frame and panel top is tempting. I love the look of those returns on the finish piece. I considered splitting my slab to accommodate the central divider but just cant bring myself to cut the 30yr old (since felled) air dried stick in half to do it. I note that wood from the same tree is incredibly stable even after extensive milling. and over a variety of temp/rh fluctuation ie.( barn to heated garage to centrally heated shop) over the last 8 months. sill if Chris estimates his buginga slab to move 1/4" I'd say the walnut will fair somewhat worse, though I cant but guestimate the true measure of movement.
I agree that calculation of the woods potential for expansion during the joonery/ design phase is crucial however this seems to be an art all its own. might we be fortunate enough to have a member with a top secret wood movement cheat sheet based on thickness,species,grain orientation, and temperature/RH fluctuations? if so I am willing to bargain paltry things, like my soul in return.

I am thinking in the near future I must see a simple frame composed with a modified mudsill joint and wedged post through tenon,very similar to andon, under glass. I think if one achieved good results post cutout it could be a most beautiful piece.
Rob S
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Chris Hall
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Re: breadboard ends( battling movement)

Sun Jan 18, 2015 10:25 pm

sill if Chris estimates his buginga slab to move 1/4" I'd say the walnut will fair somewhat worse, though I cant but guestimate the true measure of movement.
I agree that calculation of the woods potential for expansion during the joonery/ design phase is crucial however this seems to be an art all its own. might we be fortunate enough to have a member with a top secret wood movement cheat sheet based on thickness,species,grain orientation, and temperature/RH fluctuations? if so I am willing to bargain paltry things, like my soul in return.
No need to surrender your soul quite yet. Try the shrinkulator:

http://www.woodbin.com/calcs/shrinkulator.htm

I would expect Walnut, by the way, to be very stable and have minimal expansion/contraction - - one of the reasons it is one of the best choices for a slab top. Do you have a moisture meter? If not, suggest you obtain one.
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Chris Hall
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Re: breadboard ends( battling movement)

Sun Jan 18, 2015 10:31 pm

Timateo wrote:And does the season in which you build have an effect on the approach you would use?
No, not in terms of construction method. It would affect the sort of gaps you would allow on panels though. If it was the dry time of year when you built it, you could expect the panel to be at its minimum width (assuming it is properly dry), so you would fit it to the frame with the maximum necessary gap. If, on the other hand, it was at the most humid time of year, then you would do the opposite, fitting the panel so there was next to no gap. This process becomes more complicated when your client lives somewhere else with different conditions. Always allow for the movement the piece will experience in the place in which it is set.


Timateo wrote:So the next question.would an opened miter be a little much for a high end piece of furniture?


Generally, yes, to be avoided.
Timateo wrote:I would assume the more drastic the climate fluctuation the more drastic the movement in the piece. I live in tennessee where the humidity rises and drops considerably. I moved out here from seattle and this exact topic has been on my mind due to the effect it has on the overall character and finish of the piece.just food for thought if anyone cares to bite.
That is exactly the case. One of the reasons that such sophisticated construction developed in China was the large season swing in RH humidity in the region where most of the finer pieces originated.
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Re: breadboard ends( battling movement)

Mon Jan 19, 2015 4:07 am

As a rule I take it for granted that any surface wider than 15 cm has to account for some movement. (Even this rule has its exceptions and a frame gets haunched tenons in most cases.) Maybe this allowance is even generous but keeps me from confining the wood within a conception of it, that is to say within that limit the wood will dominate the concept and reveal my limitations or stupidities which I hope keeps me from complacency. For an unbroken surface, unbroken meaning just that, lets say a table-top captured within the table legs for example, I wont hesitate to glue up a core, saw edge banding and fineer - I use the Dutch word, skirting the censor every time - from my chosen slab and make up an appropriate surface, so technically that makes me less than a solid wood purist perhaps.

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