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Limitations re: tabletop size

2/6/16       
Doug Member

Website: http://DougGunn.com

A potential customer has asked for a stow-leaf dining table like the one on my website. He wants the stationary top to be 60"x60". I've convinced him to reduce that to 54"x54". Leaves would be 18" each. I would make the top at least 1-1/8" thick. There can be no battens other than breadboard ends because of the mechanism under the top. My instinct is to refuse this commission because I'd have so little control over cupping in the top, which must remain flat. In addition to all of this, the table would travel to arid Nevada after being built in Pennsylvania. I'd appreciate opinions and advise.

Stow-leaf dining table

2/6/16       #2: Limitations re: tabletop size ...
Tom Diel

I understand your concerns. I finished up reception presentation station in Oct (no good pics yet) that has a 92" x 72"top. Long grain edging and breadboard are 1 7/8"th and infill panel approx1"th. This allowed the panel tenon to be a heavy 7/16"sq with the top of the dado in the bread board to match being 7/16"+ w/ btm tongue 1" in rift white oak.

I also had a large subtop to help span the load so sagging won't be much of a concern as in your condition being supported from four legs. My suggestion maximize you size of breadboard, tenon and mortise.

If I understand won't your leg footprint be a problem unless the length of the leaf is shorter to nest leaves under the legs? I.e. leaf to be 50"L? It could be a nice setback feature to allow across the table conversation?

Still working on web redirect, time to change web hosting!!!


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2/6/16       #3: Limitations re: tabletop size ...
Gene Wengert-WoodDoc

Cupping of a top results because of mositure change--100%.--but with a glued up top, there is enough variation in natural wood behavior that moisture change alone will not create a big difference in shrinkage too create much cupping. This assumes that you are making a table top at a moisture content that is very close to the MC in use. NOTE: In my dealings with these sorts of issues, almost always the problem occurs the first year and then no further problems after that. This means that the initial moisture coming from the manufacturing is not close enough to the in-use environment causing the problem, and that the yearly changes in humidity are not that much of an issue.

So, what must also be happening to create cupping is that the bottom side is being held from moving freely...the top can move, but the bottom is restricted.

And then, perhaps there is a different finish on the bottom than on the top, which means moisture changes from month to month. The bottom responds quickly, while the top's response is delayed due to the buffering of the finish.

I suggest that you avoid this job because not dies sound like the bottom is quite a bit different than the top.

2/7/16       #4: Limitations re: tabletop size ...
rich c.

I keep getting the feeling that no one wants to glue two pieces of solid stock together on here anymore because it can cup. Using quarter sawn is a start, but with good quality stock this is not an impossibility.

2/7/16       #6: Limitations re: tabletop size ...
Doug Member

The potential problem with moisture content is that the piece would travel from a humid to an arid environment. Seasonal changes in Nevada, once the table is there, would cause minimal movement.

Top and bottom finish are identical, and each has equal number of coats. MC of lumber and shop are plus or minus 2%. Top is attached to base in slotted screw holes, and only though a structure in the center 18" of the table.

A major challenge, and perhaps the single reason I'd turn down the commission, is that the table top "floats" above the leaves on a stow-leaf table. On a 54" top with an 18" leaf on each end, the table top is attached only to an 18" fixed structure in the center.

This means that when closed, the table top rests on the closed leaf, which rests on the table base. when the leaf is open, the slides rise up and support the top. (This is why the leaf can be (and must be) the exact width of the table top). This floating isn't a problem on a 42" wide top.

The one thing that might save this job is breadboard ends, which I would maximize. Also, quartered stock would influence my decision if I can get the customer to agree to it.

2/8/16       #7: Limitations re: tabletop size ...
Doug Member

The question for me (which I see I forgot to ask) is whether a 1+" x 54" x 28" quarter-sawn hardwood top will lay flat for 100 years (roughly 28" long because it would be anchored to the base structure at one end, breadboard at other end). I'm attaching a picture of the base of one of these tables without the top, hoping it might clarify some of this. One leaf is closed and one is extended but not yet lifted up and locked into brackets. The top would sit on all of this. When I put the quesiton like this, it seems do-able.


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2/12/16       #8: Limitations re: tabletop size ...
Jason

I just finished a 72x72" table and was worried about cupping, but if you find good stock that has been dried correctly, it should be fine. If you're really worried about it being Nevada, I would go with quarter sawn stock and price accordingly. The way you describe the table, I don't see why cupping should be an issue with quarter sawn stock that was dried well.
If you're still concerned, maybe do a veneer top???

2/19/16       #9: Limitations re: tabletop size ...
Doug Member

Website: http://DougGunn.com

Yes, I think quartersawn stock is the answer. The customer has agreed to it, without reservation. Not sure he really understands why I insist on using it, but he likes the look of it and doesn't mind the cost. Having thought and talked all this through, I feel confident that this top will be fine, anchored in the center and with breadboard ends. It's not a done deal because we still haven't settled on a design or agreed to a price. But if we can, I'll be happy to take this commission.

2/19/16       #10: Limitations re: tabletop size ...
Gene Wengert-WoodDoc

To be safe, indicate that the table is designed and constructed to function between 30% to 50%RH (6 to 9% MC). When the table leaves your shop, measure the MC at several spots with a painless meter and mark the spots and record the data. If an issue arises later, remeasure the MC to determine if it is outside the 6-9%.

2/20/16       #11: Limitations re: tabletop size ...
Paul Downs

The problem you are going to run into is when the humidity changes, and the exposed top of the top and bottom of the leaf expand faster than the two surfaces that are touching each other. Tell your client to be sure to leave the leaves extended for a couple of weeks after delivery, otherwise the change in climate could well cause cupping. How do I know this? I've made lots of this type of table, both in solids and with veneered top and leaves. If you can do it, a veneered top and leaf is much better for this design.


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