Hi everyone,
Some dumb newbie questions here that should have been asked BEFORE I started the build, not after it was done.
Dumb questions:
I recently built a new coffee table out of some old oak beams. Unfortunately, the wood has moved far more than I anticipated, especially in the mitered frame and panel top. So, I ask two really stupid after the fact questions:
1. are there any good rules of thumb for anticipating wood movement in general and especially in a frame and panel design?
2. is frame and panel an appropriate design choice for such a project or should I have chosen another solution?
The Bloody Details:
The wood is from old oak beams that I reclaimed from a demolished house. They were in that house for at least 50 years and then sat in my heating room for two years before being moved to my current basement 2 years ago. Bottom line – they are dry so I didn’t expect much movement in them.
The table itself is 110cm x 90cm x 45cm.
The frame and panel construction: The frame is, I don’t even know what to call it – a lapped miter? I did a hidden lap joint…. The frame is individual boards cut from the same oak beam that have been edge jointed together. I them rebated the top to create a tongue that fits into a groove in the frame. When I first assembled the top, the panel fit tightly all around the frame. I oiled it with tung oil and waxed it with paste wax before I brought it upstairs to the living room. Within a couple of days of moving the table upstairs, I had gaps about the width of a pencil on either end of the table top.
For those who have made it this far, do you have any suggestions on how I could “hide” my mistake? NOTE: I have access to Oak, Beech, and Pine…. Nothing exotic.
Replies
The only part of the "drying history" that matters is the last bit, stored in your current basement for the past 2 years. Apparently the living room is dryer than the basement.
Frame and panel for the table is fine. Trying to hide the gaps is a bad idea. When summer rolls around the top will expand again and crush out any attempts at filling them.
Lumber moves mostly across it's width. By putting the boards across the narrow length of the table you have maximized the expansion and contraction that comes with the seasonal humidity swings. You have 9 or 10 boards moving in the panel as built.
If you had run the panel boards the long way you would only have 4 or 5 boards moving and much smaller seasonal changes.
I am discussing a project like this right now with my son. Frame and panel is a very challenging approach from the standpoint of wood movement. It can be done but there are some real design constraints and some compromises that must be accepted. Flooring people know this quite well and hide gaps at the edges of the floor underneath the baseboard. All the prep you did is step one, but you still need to follow up with proper design. But cheer up, as Jerry Seinfeld said: "pain is knowledge rushing in to fill a void" (in understanding)!
Wood expands and contracts with changes in ambient humidity, ALWAYS, and that must be taken into account. If you do not allow for seasonal changes of the field inside a frame the result can be either gapping or buckling if the frame wins the contest or splitting if it loses.
Ultimately my son has decided that discretion is the better part of valor in this case and is giving up on end grain constraints with his design.
It looks nice. I wouldn't do anything to it at this point. Live and learn.
I wouldn't call that frame and panel. The frame in a frame and panel is fixed, and couldn't open up. The panel expands and contracts within the panel. These are just mitered corners, even with the laps, and was bound to open up.
As mj said, you could have reduced the movement by half by running the center boards the long way. Or, in your arrangement, a frame with a third rail in the middle, so you would have two smaller panels to expand and contract.
I originally considered MJs suggestion of orienting the boards the long way, but in my mockup, it just didn't look right. Sorry, aesthetics.....
It is a true frame and panel in that the panel is fully free to move around. I made the tongues overly long just in case and it seems to have been one of my better decisions. But, wow, I REALLY wish I had thought of the third rail.... that is the best of set of tradeoffs for my "style" and it would have made the build easier.....
Next time, I will ask this group BEFORE I start blindly cutting things.
Thanks!
All good advice above. I will add, however, that frame and panel is a good way to deal with seasonal movement BUT, you must allow for seasonal movement within the frame. This is done by "floating" the panel in unglued grooves in the edges of the frame and the grooves (and matching tongues on the panel) must be long enough and deep enough to accommodate the movement. There are calculators on line for determining how much movement to anticipate depending on the wood species and the range of temperature/humidity expected. You can find these with a google search for "seasonal wood movement calculator".
At this point, it is difficult to tell you how to correct the problem without knowing more about how you assembled. However, I think the advice you got above on waiting a while (maybe a year) to see what it does. As long as the table stays in your climate controlled house, the effect may stabilize. Keep a watch on it and report back later and we'll see if we can figure out a fix. Keep an eye on the pull-out trays as well.
Otherwise, nice work. That's a good looking table.
This isn't a solution to the problem, but it may prevent future issues.
Wood movement is not absolute it is always relevant to the moisture content of the wood relative to the moisture content of its final destination. Those beams may not have been as dry as you thought. In my experience house that are being demolished are often left neglected for years, no heat, ac, broken windows, etc far from a controlled environment. The other thing is you mentioned they were stored in your "heating room" if this is where your furnace is and it has any type of open flame, gas oil, etc it is important to know that a by product of combustion is H²O, water vapor so in an enclosed area the relative humidity of that room is likely higher than the rest of the house.
I strongly suggest you get an inexpensive humidity gauge from Amazon and place one in that room and another it the living space to get an actual feel for the situation. I myself keep one in my shop and will place one in a clients home for a couple of weeks just to give me a fighting chance to know how tight to make door gaps and other things when I build a piece. These modern digital gauges are inexpensive and have apps that track the humidity overtime providing a pretty good picture of the environment the piece will be residing on.
I can give you two years worth of humidity data for the living room. It hovers between 30-40% for the majority of the year, with the occasional spike over 55% when I mop the floors. The house is hyper insulated - floor heating and mechanically ventilated, which explains the relatively dry environment (modern European Construction....). The basement is another topic - unheated and I don't have a humidity gauge down there. Investing in something certainly wouldn't hurt.
Another factor that affects wood movement is the grain orientation of the board. A board that is quarter sawn will have roughly half the amount of movement across its width than a board that is flat sawn. The difference may not be much but it's there and something to consider.
Christian Becksvoort has a book titled some like Understanding Wood. There is a section dedicated to woodmovement. There is a formula in there and a table with the values. Good book worth owning plus with that and a moisture meter, you no longer need to guess about likely woodmovement.
Hey, thanks for the book suggestion. I just finished the anarchists tool chest and was going to ask about book recommendations on a separate thread.
Frame & panel constructions of solid wood require that the panel float in the frame. This means that there must be expansion gaps between the frame and the panel to allow the float to cater to the humidity-change differential expansions & contractions of the frame & panel. No gluing of the two together, then, with the panel shaped to allow it to look good whilst floating.
This usually means that the panel edges are profiles so the in-out of their tongue in the frame grooves isn't so obvious. This means that frame & panel is no good for a flat table top. You picked the wrong construction method for a table top, in other words.
It is possible, though, to have a frame & panel tabletop in which there's no gap between the two and they're glued together rather than the panel floating in the frame. The panel has to be made of a non-expanding/contracting material such as MDF or plywood, usually faced with an attractive veneer.
Even then, beyond a certain size such a table top will show gaps/cracks if there's a significant humidity change in the surroundings, as the long-grain of a large frame will still expand & contract, though not so much that smaller glued frame & panel tops would crack.
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Basements or cellars are notoriously difficult to "tank" to a sufficient degree that they keep all moisture from the surrounding earth (the other side of the walls from inside the basement room) getting through into the basement atmosphere. It's the worst place you could have moved a glued-up frame & panel construction from a more normal house-level humidity where it was made.
I speak from experience. An expensive experience, in (remake it) time and timber. :-)
Lataxe