Contributor
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.Originally Posted by Eddie Ormerod
Contributor
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.
Contributor
Aj,
What do you do instead of C channel? I bought a class and that's what their recommending.
Thanks
Daniel
Contributor
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?
[OP]
Member
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?
Contributor
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.
Contributor
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/p...y-and-dryness/
Contributor
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.
Last edited by Kevin Jenness; 09-14-2023 at 4:40 PM.
Contributor
Did you angle them, or place them perpendicular to the skirt.
[OP]
Member
When you buy wood from the sawmill, how long do you let it sit in your shop before you start working with it?
Contributor
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.
Contributor
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.
Contributor
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.
Contributor
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.
[OP]
Member
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 😭
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