Tabletops Bowing Over Time

[Eddie Ormerod]

Within the last 10 years, I've built many tables.
There's been two times and now a third where after almost a year, the customer has contacted me saying their tips have bowed. All 3 tips have been maple wood.
I didn't use breadboard ends on either of them nor did I use the steel braces on the bottom.
I seal my furniture with oil based polyurethane.
I don't understand if it's something I'm doing or what's going on.
After one top warped 2 years ago, I installed the steel pieces under the top. I think they were c or U channel maybe? Anyway I never heard back from the customer so maybe they worked.
I guess I have to make another top or try the braces. I'm just not sure what is going on here.
And I live in Kentucky.
Any suggestions?
Thanks
Eddie

[Edward Weber]

Need more information than what they're made of and finish.
Do you use an apron or some other type of stabilizing support underneath or are they just slabs.
If it's the latter, they're gonna bow or warp or somehow move out of shape, that's what wood does unless you control the movement by some method.

[Jim Becker]

If these tables are being used in a commercial situation and enduring a constant stream of cleaning cycles, it would behoove you to make the C-channel a standard feature. Also consider how you are holding the tops on whatever is under them...it has to accommodate wood movement, but also disallow any cupping/warping, too, over time. Even "sealed" with the oil based finish, moisture and temperature are still a factor and wood moves because of them.

[Richard Coers]

How did you fasten the tops of the tables to the leg assembly. I've never had a call back on a table, and I've been making them for over 50 years. The size of the top means the wood can shrink from around 1/4-3/8" across the grain. Do you finish the bottom of the top? That's very necessary for a flat top.

[Matt Lau]

Any pictures of your work?

First thing that comes to mind is lack of lateral support.
It's something that Stan Covington strongly advised me on in constructing stuff.

[Eddie Ormerod]

It's a dining room table. I used figure 8 fasteners on top of aprons to the underside of top.

[Eddie Ormerod]

The top is 72x42, 1 1/2 thick. Whole thing is stained and polyurethaned. No c channels or breadboard ends. Mounted to aprons with figure 8 fasteners. I always use those to allow for movement.

[Andrew Hughes]

In my mind a 1 1/2 maple top shouldn’t warp if the wood is kiln dried. So my guess from a thousand miles away is the figure 8s aren’t allowing enough movement. Other reasons I’ve seen wood cup or warp is direct sunlight heating the surface.
Careful selection of wood for table tops are critical too me. A tables top demands the best boards for look and stability
I also think adding c channel to the underside is blasphemy and highlights the craftsman’s lack of experience or confidence.
Good Luck

[Mel Fulks]

I blame the top…or whoever put a safe on top of the top. And a 3 inch thick top would stay pretty flat , unless used for one of those
lady riding a donkey shows.

[Richard Coers]

This is the pinnacle of my career. 4'x12' mahogany and painted plywood.
507613

[Bill Dufour]

Tips? Are the figure eights at 45 degrees to the grain. Screws not too tight.
Bill D

[Eddie Ormerod]

Fasteners were on the ends of the tables. A couple on the linger aprons. Screws definitely not tight

[Eddie Ormerod]

I'm taking your advice and tips. The house is a fairly new built house. Within a couple of years. The table is in their kitchen area. Back in March I dropped it off. She sent me pics of it last night showing the edges raising up.
I'm gonna have to build her another top I guess😭
I just don't know what caused this. It's about the 3rd or 4th one within probably a 100 tables.
I want to send you guys a pic but don't seem to know how.

[lou Brava]

Well if it's only 3 or 4 out of hundred your doing pretty damm good ! & if it's the same table, same wood type, same moister content & construction method & similar climate it's defiantly a head scratcher. I can't see how a figure 8 installed right or wrong would cause a table top edge to raise or warp.

[Edward Weber]

IF, the table is in the direct flow path of a forced air HVAC system, this could have an effect on the top.
Once again, IF the table is in this path, the wood may not be able to recuperate, or balance out before the next heating/cooling cycle begins. This drying becomes slightly greater with each cycle of the HVAC and eventually starts the warping.

[Richard Coers]

Fasteners were on the ends of the tables. A couple on the linger aprons. Screws definitely not tight
The longer aprons are the critical ones. Like Bill mentioned, the figure 8s are likely still restricting it. I also suspect the wood if all these happen in the first year or so. That would suggest the wood wasn't 6-8% moisture and the seasonal swing did the damage.

[Richard Coers]

IF, the table is in the direct flow path of a forced air HVAC system, this could have an effect on the top.
Once again, IF the table is in this path, the wood may not be able to recuperate, or balance out before the next heating/cooling cycle begins. This drying becomes slightly greater with each cycle of the HVAC and eventually starts the warping.
No way does a sealed table top move enough between cycles of furnace or AC. Or do you mean each season? Now if the table was sitting by a wood stove or fireplace, that's a different story.

[Daniel O'Neill]

Aj,
What do you do instead of C channel? I bought a class and that's what their recommending.

Thanks
Daniel

[Kevin Jenness]

Sounds like the movement is cupping, across the width of the top, and that is generally caused by a significant (>2-3%) long-term moisture content change in the wood between fabrication and installed conditions. I would be looking at the relative humidity in the customers' homes vs in your shop and possibly the mc of the lumber when fabricated as factors. Is your shop climate controlled? Are the homes? Did you check the lumber mc before making the tops or in service? Were the troublesome tops made in a period of high or low humidity? Did you ship the tables to a region with a consistently lower or higher rh than your area?

[Eddie Ormerod]

I don't understand how the humidity in the house will affect the tabletop. It went from being dried in a kiln to the sawmills garage. Then to my shop, then to the customers house. I know the humidity levels are different in every place but how do I keep the top from bowing or cupping when it gets to the customer's house?

[John Kananis]

Make sure it's dry before using and don't take the sawmill's word for it. I know what its like to need material right now but I try and buy a little ahead so it has time to "sit" in my shop.


I don't understand how the humidity in the house will affect the tabletop. It went from being dried in a kiln to the sawmills garage. Then to my shop, then to the customers house. I know the humidity levels are different in every place but how do I keep the top from bowing or cupping when it gets to the customer's house?

[Edward Weber]

No way does a sealed table top move enough between cycles of furnace or AC. Or do you mean each season? Now if the table was sitting by a wood stove or fireplace, that's a different story.
Big, easy to understand numbers
If an HVAC vent blows on a piece and dries the wood a few percent, say 5, then it only recuperates 4 percent moisture when the HVAC is not on, it lost 1 percent moisture. After this cycle repeats itself of drying, it is cumulitive.
The numbers are no where near this high
I'm not saying it's an over night situation, far from it, but being subjected to repeated cycles of forced dry air, will most definitely dry out a piece of furniture.
Here is just one of many sources that go into more depth than I care to.
https://www.dutchcrafters.com/blog/protecting-solid-wood-furniture-managing-humidity-and-dryness/

[Kevin Jenness]

I don't understand how the humidity in the house will affect the tabletop. It went from being dried in a kiln to the sawmills garage. Then to my shop, then to the customers house. I know the humidity levels are different in every place but how do I keep the top from bowing or cupping when it gets to the customer's house?

Ideally the lumber will be stored and milled at a moisture content close to what its in-service conditions will be. If the house's average relative humidity is significantly different from the conditions the lumber has reached equilibrium with when it is made the tabletop will probably show some cupping. You can't control the customer's house but you can control or at least monitor your shop conditions and the lumber moisture content and work accordingly. You may assume the lumber you are using is "dry", but unless you measure that and compare it to what it's going to be in use you are flying blind.

If you build a table in Mississipi in the summer in an unconditioned shop and put in an air-conditioned house or send it to Arizona you had better use lumber that you know is <8% mc, keep it covered or dead-stacked in your shop as you work it, and finish and ship it as soon as possible. Acclimating lumber to a shop that is way different than the expected in-service conditions is asking for problems. You can reduce cupping by using quartersawn material.

[Richard Coers]

It's a dining room table. I used figure 8 fasteners on top of aprons to the underside of top.
Did you angle them, or place them perpendicular to the skirt.

[Eddie Ormerod]

When you buy wood from the sawmill, how long do you let it sit in your shop before you start working with it?

[Kevin Jenness]

When you buy wood from the sawmill, how long do you let it sit in your shop before you start working with it?

It depends. If I know it's been in a stable environment and the moisture content is appropriate for its intended use I may dice it up as soon as I get it in the shop. If it's been stored in an open shed or completely unconditioned space I may want to let it sit on stickers for weeks or put it in my kiln. Thicker, denser material usually takes longer to acclimate. The key is knowing what the mc is before use.

[Cameron Wood]

How are figure 8 fasteners going to cause the edges of a table to curl up? The focus on this makes no sense to me.

If the wood was quite dry, and moved to a more humid condition, the fewer coats of finish on the underside could allow more moisture to be taken up there.
Just a WAG.

[Richard Coers]

Aj,
What do you do instead of C channel? I bought a class and that's what their recommending.

Thanks
Daniel
C channel is the new internet way of making tables. Tables have been made for hundreds of years, even before steel was made. Think about how they got by. I've made tables for 51 years (24 professionally) with no steel and no call backs. Thick hardwood has more strength in moving that a lot of small cross section steel and will just take the steel with it. Many folks even fasten the steel hard to the wood and make the situation worse. The keys are kiln dried wood, and designing room for the wood to move from season to season.

[Richard Coers]

How are figure 8 fasteners going to cause the edges of a table to curl up? The focus on this makes no sense to me.

If the wood was quite dry, and moved to a more humid condition, the fewer coats of finish on the underside could allow more moisture to be taken up there.
Just a WAG.
If the figure 8 is installed perpendicular to the side apron, and the wood expands or shrinks, the figure 8 locks it to the apron and something has to give. The table top is not floating on the base.

[Eddie Ormerod]

I'm.nit sure. She sent me pics. It's definitely raised up. I don't know what to do different when I make her a new top 😭

[Eddie Ormerod]

So I just left the couple's house. The 1 1/2 thick top is made of 6) 7 inch pieces of wood glued together. The last board has cupped up from the base. I'm 235 lbs and couldn't even get it pushed down on to the base.
I told her I'll make a new top. She doesn't want breadboard ends. I told her about the c channel steel pieces. I told her I will pay for the top and asked her to pay for the c channel. She acted like she didn't want to.
So I told her to give me a couple of months to get it in my shop, mill it down slowly and I hope this doesn't happen again.
Eddie

[Frank Pratt]

I told her I will pay for the top and asked her to pay for the c channel. She acted like she didn't want to.
Eddie
I don't think it's right to even suggest that she pay for the C-channel. It's up to you to build it right or fix it free of charge.

[Michael Burnside]

I don't think it's right to even suggest that she pay for the C-channel. It's up to you to build it right or fix it free of charge.

+1 especially if you want any repeat business. I'd be miffed if I was asked to participate in the cost of repairs.

[glenn bradley]

I'm sure you picked up on the reaction to asking a client to pay for a problem with your product :rolleyes:. That aside, I may have missed it but did not see how you account for movement. It doesn't really matter how as long as you do. Since you have had 90+% success I assume you have a method. Also the fact that the outer edges are raising doesn't really point to an absence of buttons, z-clips, figure 8's, slotted holes, or some other method of movement allowance. Is it always an outer, unsupported edge?

[Cameron Wood]

Did you ask if she irons her clothes on that table edge? ;)

[mreza Salav]

So I just left the couple's house. The 1 1/2 thick top is made of 6) 7 inch pieces of wood glued together. The last board has cupped up from the base. I'm 235 lbs and couldn't even get it pushed down on to the base.
I told her I'll make a new top. She doesn't want breadboard ends. I told her about the c channel steel pieces. I told her I will pay for the top and asked her to pay for the c channel. She acted like she didn't want to.
So I told her to give me a couple of months to get it in my shop, mill it down slowly and I hope this doesn't happen again.
Eddie

Maple is not the most stable wood. Pick a thick board that has sat for years, cut it, leave it for couple of days and it moves. It is worse with wider planks. I am not in the business but have seen enough that if I was doing this for a living would avoid using wide (like 7" that you say) in those situations.

[Mel Fulks]

I would screw on some battens….on the BOTTOM of the TOP ! Seen lots of them ,they work.