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post #1 of 13 Old 02-13-2011, 08:59 PM Thread Starter
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Breadboards/wood movement question...

All,

I am a budding woodworker and am in the process of making a coffee table and was hoping to tap the considerable knowledge base here for some advice regarding the amount of movement I can expect in the tabletop. The top is approx 36" x 20" and is made of 27 planks of red oak (lowes) 1" x 2" that I have face glued to each other along the long dimension.(I.e. the grain runs the 36" length) The resulting slab is a satisfyingly solid 1.5" thick slab of oak..with a 'butcher block' look to the ends and a nice variation of grain pattern thru the top.

I am not entirely certain, however,that I like the exposed end grain butcher block look however and am considering putting breadboards to cover the ends. I know that all wood suffers some movement and I was wondering what your thoughts were on how much I should expect across it's 20" width. If the movement is negligible it would certainly be easier to mechanically fasten thru simple dowels and glue/etc the breadboards end caps without actually making them functional in the traditional sense.


Thanks in advance for your time,

-don

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post #2 of 13 Old 02-13-2011, 09:07 PM
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Welcome to the forum. I beleive it's all about the EMC of it's final destination but Ill watch and learn with you.

"IF IT'S TOO TOUGH FOR THEM, IT'S JUST RIGHT FOR ME"
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post #3 of 13 Old 02-13-2011, 09:15 PM
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Originally Posted by alterd View Post
All,

I am a budding woodworker and am in the process of making a coffee table and was hoping to tap the considerable knowledge base here for some advice regarding the amount of movement I can expect in the tabletop. The top is approx 36" x 20" and is made of 27 planks of red oak (lowes) 1" x 2" that I have face glued to each other along the long dimension.(I.e. the grain runs the 36" length) The resulting slab is a satisfyingly solid 1.5" thick slab of oak..with a 'butcher block' look to the ends and a nice variation of grain pattern thru the top.

I am not entirely certain, however,that I like the exposed end grain butcher block look however and am considering putting breadboards to cover the ends. I know that all wood suffers some movement and I was wondering what your thoughts were on how much I should expect across it's 20" width. If the movement is negligible it would certainly be easier to mechanically fasten thru simple dowels and glue/etc the breadboards end caps without actually making them functional in the traditional sense.


Thanks in advance for your time,

-don

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Wood moves more across the grain more than with the grain. You have glued the faces where if there was movement it would be up and down between the pieces. Since the width of those pieces is 1Ĺ", there may or may not be movement. It's just one of those things in nature. As for the overall of the 20" lengths, breadboard ends would take in any movement in account, and would dress up those edges. I'm thinkin' the movement on those ends would likely be minimal.








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post #4 of 13 Old 02-13-2011, 09:52 PM Thread Starter
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Thank you much for speedy reply(s)! So do you think a simple mock- breadboard that is not designed to float (I.e. No MT design and pegs in elongated holes) would likely suffice? That is since the predominant motion would be up and down and not across can I simply glue and screw/peg a breadboard to the ends?

Thanks again for your time, it's much appreciated.

-don

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post #5 of 13 Old 02-13-2011, 10:06 PM
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Thank you much for speedy reply(s)! So do you think a simple mock- breadboard that is not designed to float (I.e. No MT design and pegs in elongated holes) would likely suffice? That is since the predominant motion would be up and down and not across can I simply glue and screw/peg a breadboard to the ends?

Thanks again for your time, it's much appreciated.

-don

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I would still allow for some movement.








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post #6 of 13 Old 02-13-2011, 11:06 PM
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Don, you may have the answers you need already, but when you say "face glued" and use the term "butcher block look to the ends" that could be take either way (by me anyway). Since you said you're a budding woodworker I just want to clarify terms. You do know the difference between "face" glued and "edge" glued correct? I know that sounds like an obvious question but when I was a budding woodworker I could not keep most of the terms straight so the only reason I ask is for clarification.

The important thing to remember is how and why wood moves. It's also important to remember that wood movement with an edge-joined glue-up is cumulative - the same as a solid piece of the same species. Sure the glue lines take some of that away but it's not measurable with a shop rule.

So if you have a solid board of red oak 30" wide, it will shrink tangentially at let's say ~10%. A 30" red oak edge to edge glue-up of whatever width pieces (just pick one) will shrink at the same % for all practical purposes. I mention this because it's a myth that a table top made up of narrower flat grain, edge-glued pieces will experience a lower rate of accumulative shrinkage across the grain than a solid piece simply because the pieces are narrower. This is common sense to most but for whatever reason it is also a common myth on many forums.

If your pieces are face glued as you say, the % of movement perpendicular to the face grain is still the same, but not cumulative across the width of the top other than the radial shrinkage of the individual pieces which let's just agree will average 5%. That is also cumulative and either way adds up siginificantly where large MC %s are seen.






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post #7 of 13 Old 02-14-2011, 08:44 AM Thread Starter
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Don, you may have the answers you need already, but when you say "face glued" and use the term "butcher block look to the ends" that could be take either way (by me anyway). Since you said you're a budding woodworker I just want to clarify terms. You do know the difference between "face" glued and "edge" glued correct? I know that sounds like an obvious question but when I was a budding woodworker I could not keep most of the terms straight so the only reason I ask is for clarification.

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@TexasTimbers -- Yes I _think_ i have my terminology correct re: face glued vs. edge glued. I have taken stock red oak 1"x2"s and glued them face-to-face making my table top 1.5" thick (the actual width of the stock board) and 20.25" total inches in width (27 boards x .75")

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If your pieces are face glued as you say, the % of movement perpendicular to the face grain is still the same, but not cumulative across the width of the top other than the radial shrinkage of the individual pieces which let's just agree will average 5%. That is also cumulative and either way adds up siginificantly where large MC %s are seen.

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I thought I was following your detailed explanation until the bit above where you say its 'not cumulative across the width of the top...' but then say a sentence later 'That is also cumulative and either way...' ???

Regardless, it seems my takeaway is that if I am going to have a breadboard on this piece I need to allow for some movement or hazard the risks.

Thanks guys,

-don
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post #8 of 13 Old 02-14-2011, 12:06 PM
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... but then say a sentence later 'That is also cumulative and either way...' ???
...
Yeah I think my organic cache had just gotten full after the previous sentence. Ha.

Here's a picture, even though I think you have a handle on it I don't want to mislead later lookers.


Name:  Wood Moves.jpg
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Attaching a breadboard to the end of face glued top (A) isn't something I would suggest, but if you do make sure the breadboard is flat sawn with the long grain perpendicular to the top's end. And don't rout a groove into the breadboard edge - rout the groove into the end of the face-glued top and put the tongue on the breadboard.

The way the grain's oriented on a face-glued top means that it'll expand and contract in height, and if the breadboard edge had the groove then the tongue of the top could theoretically expand enough to asplit the grooved bredboard apart to some degree, or even expand enough that it wouldn't allow the slippage a T & G breadboard is designed to give which could also cause splits.

But even with the groove on the edge of the top, if it shrinks enough it could clamp down on the tongue enough to prevent the desired slippage too. So for this reason I don't like the face-glued tops for use with breadboards. Even by incorporating large enough tolerance in the T & G you then have to find a work-around for a sloppy and loose breadboard.

Some may say I'm making it too hard, but if you're building furniture might as well try to eliminate as many potential problems as possible no matter how small.








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post #9 of 13 Old 02-14-2011, 12:10 PM
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One more thing. Longitudinal shrinkage is actually the least but it's not really in play in this application so I didn't even address that. It's not even measurable in most species over such short lengths.






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post #10 of 13 Old 02-14-2011, 01:04 PM
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May I ask then wha is the best way to attach a breadboard?
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post #11 of 13 Old 02-14-2011, 01:23 PM
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May I ask then wha is the best way to attach a breadboard?
I wouldn't say there's always a single best way. There're many ways to do it - just as long as your joint allows the top to expand and contract without the breadboard hindering that movement, and the breadboard and top look good together then I think you could call that good enough if not best.

The vast majority of tops and lids are made of flat grain wood, whether a solid piece or a glue up it doesn't matter. So the use of a flat grain with some kind of T & G or sliding dovetail is used the most (I believe). The T & G are usually pegged with elongated slot on the tongue portion which is cut on the end of the top or lid, so the the pegs don't stop the top from moving.

The breadboard peg holes are the same size as the pegs and glued in place. the dowel hole placement is such that the dowels keep the breadboard groove ends pulled tightly against the top so that it looks good. I have also seen spaced mortise and tenon used for this especially on thicker tops, sort of like a broken-up T & G also employing dowels.

Remember the point of a breadboard is to prevent the top or lid from cupping as much as possible.
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post #12 of 13 Old 02-15-2011, 09:02 AM Thread Starter
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@Texas -- Thanks again for all the info..the picture was worth a thousand words.

However, before reading your post and under the assumption I would need a classic breadboard, I have already cut the tongue on the tabletop... but after reading your post i am now hesitant about attaching the breadboard itself for fear of it splitting... (your analysis made perfect sense to me).

Short of cutting the tongue off, I had the idea that if I face glued a couple of 1x2 boards to serve as the breadboard and then routed the groove into the face side, the expansion and contraction of the breadboard would seem to then match that of the table. Is this flawed logic?
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post #13 of 13 Old 02-15-2011, 01:38 PM
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You might cut the tongue off and groove both the breadboard AND the top, then use a stopped spline to join them. This spline would need to be pretty wide and the grooves deep. You would have to dowel both sides of the top, but you can make the dowels blind by using a mushroom head and gluing them from the bottom into recesses to keep them flush. You just want to make sure the glue doesn't squeeze out and into the slotted holes where movement must occur. Also coat the spline and grooves with beeswax. This option also does not shorten your top any.

I would also seek other opinions, there may be a better solution that I'm not thinking of.







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