Three years ago, I purchaseda wooden table, stained mahogeny for $50. It was originally a $500 table, but the table top split along the length of the table. I figured I could place wood filler, sand and stain. Unfortunately, the gap widens in the winter and closes in the summer.
Obviously, I am not a wood furniture expert, but I'd like to improve the table. I've heard many different opinions:
*glue the pieces together using a clamp to pull the table top closer,
*sand the whole table down, let it fully dry out, then stain and apply a butterfly strap
*refill the crack, stain it and then place lacquer over it
I can't seem to get a straight answer. I know the root problem is humidity, the wood was probably not cured. Where do I go from here?
There are a couple of ways to attack the problem, but it is difficult to assess without seeing the table, therefore, I doubt anyone can give you a definitive answer with just the information provided.
Can you post pictures of the table in abpw, or provide a url?
Is it a plain table top? How is it attached to the aprons? Do you have a table saw?
Look underneath and see how the table top is attached to the apron (assuming there is one). If the top is not allowed to move with changes in temperature and humidity it'll split. The preferred way of attaching the top to the apron is with clips, or at the very least ovalized holes in the apron so the screws can slide a bit.
If there's no apron, and it's just the top, then the wood might not have been fully dry before the table was made. That sort of crack is called a check and it doesn't necessarily affect the wood strength that much, but it is unsightly. Unfortunately I don't know of any way to successfully repair such a check - they'll almost always open up again if the repair isn't strong enough, or will open up in a nearby location.
George Nakashima, the wonder of woodworking, would often use dovetails to splice together pieces and even strengthen such checks. He didn't avoid imperfections in wood as they were part of the wood's soul as far as he was concerned. Whether that could be done on you table is dependent on the style, and could look very out of place.
If your house isn't maintained at a constant temperature and humidity (unlikely unless you live in a museum) the wood will move. The amount it moves is dependent on the species, the amount of change in humidity and the width of the top. Do you have forced air heating and/or no air conditioning?
Here's what I'd do... Remove the top, rip the top down the slit and joint the edge. Install a biscuit every 8", glue up and clamp. Allow the joint to fully cure for 2 days. Refinish the top and attach to the base.
If the source of the problem is how the top is attached to the rails, as others have said, it's just going to crack again somewhere else down the road. Treat the source first. More than likely the top is screwed to the rails with pocket screws. That's bad.
I'd be nervous about trying to rip the table. The edge may not be straight anymore which would be a hazard trying to feed a heavy table top through a table saw. I'd feel better with a straight edge and circular saw. But then who knows what stresses in the table are going to be released by the cut, the edges may require jointing even if you get a clean rip. It may work, it may open a can of worms. I'd be more inclined to pull it together with a clamp and then put a couple pocket screws in the underside if there isn't enough room to get glue in it.
Ok, I've looked at the underside of the table and here's what I found:
The table top is screwed in at several points (5x along the lengths, 4x along the widths, plus two bars along it's width with 4 screws each). Would there be some way to restore the moisture in the wood (via oil or other methods) and then seal the table with a lacquer to prevent the moisture from leaving?
The fact that the gap widens in winter and closes in summer is odd, well, it's odd considering that humidity is usually lower in summer, so I'd expect the table to shrink and the gap to widen. Of course if it's in a well heated room in winter, that may be the course of the inverted phenomenon.
What you describe often happens when somebody tries to attach wood along the grain to wood across the grain, the two rails across the grain under the table may be the problem if they are attached in a way that they don't allow for expansion and contraction. (Could be done with oval holes and washers under the screw heads).
The top needs a floating attachment to the rails, or the whole thing will likely happen all over again after you fixed it.
I'd first try this: get some sash cramps from somewhere if you don't have any. For a dining table probably 8. Remove the top from the carcass and see how you can pull it together with the cramps, using half from below and half from above the timber (and use pads to protect the timber!) if you can pull the crack tight that way so it's nearly invisible, without using huge amounts of brute force, then you can glue it without jointing - you just need to get glue into the crack ...
Then use a technically correct way of reattaching it to the rails. My preferred method is to rout a groove into the rails, and slot custom made L-shaped blocks of hardwood into the groove then screw them to the tabletop from below. This allows for movement while firmly holding the top. But you can actually also get special metal brackets for the purpose. Any good joinery trade supply [shop] should carry something like that.
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