Design for wood movement vs. aesthetics

[wtnhighlander]

I have a pub-style table buuld coming up, which presents me with a question to bring to the group. Considering the environment will not be 100% temperature & humidity controlled, which is the better choice?

Use a simple edge-glued slab for the top, like this (forgive my finger painting, working from my phone):

 

Or use a 4-quadrant radial pattern:

One requirement is that the outer rim of the circle has a contrasting layer underneath. 

The edge-glued top with certainly expand and contract itself out of roundness, possibly spoiling the reveal of the contrasting rim below.

I feel like the radial pattern would move evenly around the circle, but joining the quadrants this way has me concerned that they might push themselves apart.

Any experience or opinions to share?

[Mark J]

No real world experience, but I think you are correct that plan B will tend to push itself apart.  This could be mitigated with some expansion space between each quadrant.  But then when the beer spills....

[BillyJack]

What do you mean by a contrasting layer beneath?

We made restaurant tables from 8/4 for years . If you restrict it's movement it will cup on you. You have a moisture issue. Sometimes a sustrate with veneer or thin pieces followed by epoxy would be best...

 

[treeslayer]

17 minutes ago, wtnhighlander said:

has a contrasting layer underneath. 

does it have to be flush with the top or can you set it back say 1/2"

[BillyJack]

43 minutes ago, treeslayer said:

does it have to be flush with the top or can you set it back say 1/2"

Possibly a apron maybe?

[Chestnut]

Might need a bit more detail but I'm afraid your 2nd sketch would not far well. In that sketch you have grain intersecting  perpendicular. This would cause long grain to try and restrict  the expansion and contraction of the boards perpendicular to that long grain. I made a table like that once .... yeah it exploded.

I"m not sure the effect you are trying to go for but if there is a 2 tone unfortunately the best way may be a subtop out of the different species. Make sure that both the subtop and top and oriented in the same direction and they should expand and contract similarly enough to not cause problems. Yes they may be "out of round" as seasons change but i doubt customers are going to bring in a compass and try and prove that. Unless of course these tables are going in the math department or engineering department at a local university.

[BillyJack]

20 minutes ago, Chestnut said:

Might need a bit more detail but I'm afraid your 2nd sketch would not far well. In that sketch you have grain intersecting  perpendicular. This would cause long grain to try and restrict  the expansion and contraction of the boards perpendicular to that long grain. I made a table like that once .... yeah it exploded.

I"m not sure the effect you are trying to go for but if there is a 2 tone unfortunately the best way may be a subtop out of the different species. Make sure that both the subtop and top and oriented in the same direction and they should expand and contract similarly enough to not cause problems. Yes they may be "out of round" as seasons change but i doubt customers are going to bring in a compass and try and prove that. Unless of course these tables are going in the math department or engineering department at a local university.

He mentionedit may not be an acclimated environment  which throws everything into  an interior/ exterior setting. 

We had to make IPE tables for an exterior restaurant  one time...But.... confused on this setup...

 

[Chestnut]

I guess his main question was design for wood movement or aesthetics. To answer that question ultimately design for wood movement as that will cover both. Designing for aesthetics  may cause the table to fail in a way that will ruin the aesthetics.

[wtnhighlander]

Thanks all. I believe @Chestnut has the best answer regarding movement, make a sub-top.

The sub-layer is 4/4, surfaced as thick as I can kerp it, just like the main top. It is supposed to protrude slightly all around. Here's another finger-painting to illustrate the edge profile:

 

Current plans are red oak for primary wood, cherry for the accent. Intended to compliment the bar I made for the same guy last summer. 

I hope to avoid an apron, and plan to include corbel-ish cross bracing for support underneath, with the top panels overhanging the support by 3" or so. The base pedestal is still under discussion, but I think he's leaning toward a fat, tapered cone with a weighted bottom. There may be some coopering in my future!

[Chestnut]

You could probably make the subtop a doughnut shape with the center not filled in to save material. I like the idea. I hope you share the end result with us.

[BillyJack]

You don't want to put two tops together. That's a no-no. Even a solid top with a 3"  solid wood band is a no-no... cherry and oak will move at different rates. It's your table, enjoy....

[wtnhighlander]

1 hour ago, BillyJack said:

You don't want to put two tops together. That's a no-no. Even a solid top with a 3"  solid wood band is a no-no... cherry and oak will move at different rates. It's your table, enjoy....

I had suspect that could be a problem. My original thought was to make the bottom layer as a 'wagon wheel', with mitered boards to form the rim. I'm now leaning toward a 'donut' ring as Drew suggested. In the direction of the grain, include one board the diameter of the ring as part of the glue-up. The otger 'spoke' of the wheel, being across the grain, would be half-lapped, joind with slotted screws. Then the solid top layer joind to tge ring, again with slotted scrws to allow movement. Hopefully that would allow enough slip to avoid warping, and keep the diameters relatively close. 

The corbel-ish supports would attach to the 'spokes' of the wheel, also with screws in slots as needed.

[Chestnut]

6 hours ago, wtnhighlander said:

I had suspect that could be a problem. My original thought was to make the bottom layer as a 'wagon wheel', with mitered boards to form the rim. I'm now leaning toward a 'donut' ring as Drew suggested. In the direction of the grain, include one board the diameter of the ring as part of the glue-up. The otger 'spoke' of the wheel, being across the grain, would be half-lapped, joind with slotted screws. Then the solid top layer joind to tge ring, again with slotted scrws to allow movement. Hopefully that would allow enough slip to avoid warping, and keep the diameters relatively close. 

The corbel-ish supports would attach to the 'spokes' of the wheel, also with screws in slots as needed.

The expansion and contraction difference between red oak and cherry is 1.5% so if the oak will expand 1/8" the cherry would expand 1.5% less than 1/8". That's around 0.00187". Very minimal.

[BillyJack]

3 hours ago, Chestnut said:

The expansion and contraction difference between red oak and cherry is 1.5% so if the oak will expand 1/8" the cherry would expand 1.5% less than 1/8". That's around 0.00187". Very minimal.

It just means you'll have a Crack eventually. You cannot lock a solid top on movement. As mentioned in the beginning ......not acclimated.....

[Chestnut]

A sub top is attached with screws to allow movement. I in no way suggested to constrain wood movement.

[BillyJack]

Non acclimated. Very risky no matter how you prep. 

[wtnhighlander]

Just so you know that finger-painting isn't my only design tool, here are a couple views of the model currently under consideration:

I call it 'ToadStool'.

The base in this design is weighted for stability. Gold is red oak, red is cherry. FreeCAD includes no textures by default. Now the question is if I should incorporate 3 leveling feet under the base, or just rely on the compression of the rubber footpad material to prevent rocking. The floor is stained concrete. Pretty smooth, but you know...concrete.

@BillyJack, your concern is noted, but the 2-layer top will be joined with screws only, in slotted holes to allow movement. I'm confident the results will be stable enough.

[Mark J]

Speaking as a potential pub goer I don't want my table to rock.  Three leveling feet, please.

[Martin-IT]

On 1/18/2020 at 10:36 AM, BillyJack said:

What do you mean by a contrasting layer beneath?

We made restaurant tables from 8/4 for years . If you restrict it's movement it will cup on you. You have a moisture issue. Sometimes a sustrate with veneer or thin pieces followed by epoxy would be best...

 

Question: is the top veneer on plywood ? How to keep the circle going around from cracking with expansion/contraction ?