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post #1 of 27 (permalink) Old 03-19-2016, 10:22 PM Thread Starter
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Default Edge Joining Boards

My wife has a little oak table that she picked up at the flea market. It did its job well for a couple of years, but then the glue in the glued-up top failed. The top separated into three boards.

The boards were joined together with a very old style tongue and groove. There was no way I could get the boards to go back together without removing the glue, which was a pain. Even then, I was never able to get the boards back together.

Since she told me I could trash the table if I couldn't fix it, I took my router with a straight but and removed the tongue on each piece by routing up to the edge using a Bora-type clamp as a straight edge. It took over an hour to get it right because I had to make sure the clamp was parallel and that I wasn't taking off too much wood.

After I removed the tongue, and took off a very small amount of wood on the groove side to make sure that the face was clean. That worked out well. Then I put biscuits in each side and glued the boards together.

However, when I joined the boards, the outside edges were flush, but there is still a tiny gap in the center of the table. The gap looks as if the clamp/straight edge flexed a little when I was routing. If you look at the clamp, I don't think there is a chance that it flexed. If I had bumped it loose from the ending side of the rout, the ending edge would not be correct.

Can you share any ideas about why there is a gap between the boards in the middle but not in the end? The gap is not bad enough to worry about, but it's clearly there. (I would have taken the setup to my friend who has a jointer, but the outside pieces of the table tap are glued to the legs and tray at the bottom, so that wouldn't have worked very well.)
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post #2 of 27 (permalink) Old 03-19-2016, 10:32 PM
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My first guess is that the space that is there now may well have been the cause of the glue failure in the first place. Of course, that's hard to tell, but could be.

Did you do a dry run first? That should have showed up any potential spaces in those boards.

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post #3 of 27 (permalink) Old 03-19-2016, 10:37 PM
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I would have cut off the tongues as precisely as possible, then routed a groove on each side of the board, then cut a spline to fit the groove, then glued them up with clamps and cauls. If the tongue is cut with all boards face down on the table, the top should wind up flush and any sanding to level the underside up would be on the bottom, out of sight. The cutter for the groove would have cleaned out any glue, and you could make two passes to widen the groove slightly . With a trial fit, you could tell where the gap was, then use a hand plane to straighten out the piece(s) until it was a perfect fit, then glue. You would still have 99 percent of the full width when you were done.
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post #4 of 27 (permalink) Old 03-19-2016, 10:43 PM
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BTW, you could still cut the pieces apart with a very straight rip cut down the line of the gap. Need to set such a cut up carefully and use a glue line type blade. Then you will have the same as a planed, straight edge that can be re-glued. Use a narrow kerf rip blade. I'd use my narrow kerf, Freud Glue Line blade for that after making certain my fence was a close as possible to parallel with the blade. And I'd double check with a Wixey digital gauge, to make sure the blade was exactly 90 to the table. You will likely lose about the same width with this approach as with a hand plane.
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post #5 of 27 (permalink) Old 03-19-2016, 11:21 PM
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I think his question is more on why did this cut end up this way it did when the guide is stick straght, why didn't the cut mimic the clamp guide?

First, even if you push that saw tight against the clamp and know 100% for a fact it stayed super tight against the clamp the blade can wander. It wanders very, very little in these cases and most likely caused by the wood itself , either from an internal stress or grain characteristic that the blade just had to follow.

Second reason is near the first except the wood caused the saw itself to wander ever so slightly in the same manner and reason described for the blade. The saw left the clamp or the saw titled ever so slightly as you went from end to end.

This is why the track saw was developed. A track saw keeps the saw perfect straight and eliminates the saw from wandering due to wood stress or the saw leaving the edge of a guide. But I have seen blade wander even using a track saw, especially with a thin blade.

Also, unless a person is very skilled and the set up, saw, blade and wood(plywood is far better than hardwood) all perfect the method you used is never an ideal nor easy way to get two boards to line perfectly. The Bora clamp method is great for squaring things up, but joining or jointing two pieces calls for more precision than a setup like this offers. Still, if you used a track saw you would have had a far batter chance of getting good results.

One more thing, the wood could of actually moved after you cut it. Don't laugh, the stress in wood causes this all the time.. I make pieces that consist of geometric shapes and I cant cut the parts unless I know I can glue them up the same day for this very reason. The next day the pieces wont fit flush with a jointed like seam. The longer the parts are the more likely this can happen.

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post #6 of 27 (permalink) Old 03-19-2016, 11:37 PM
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You only took a fine shaving off either side at the most and that shouldn't be enough to affect the boards tension. I'm not familiar with the Bora but it would need to be pretty stiff to eliminate that as a possibility and in fact, the problem occurred where it be most likely to if the straight edge were the problem. Its too bad you didn't find the problem before the glue up because it would have given you a chance to try to find the cause and fix it. Anything we can suggest is pure conjecture at this point.
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post #7 of 27 (permalink) Old 03-20-2016, 04:54 AM
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Can you fill it in with a clear epoxy or resin?
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post #8 of 27 (permalink) Old 03-20-2016, 05:46 AM
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Hey Mike, before I would repair the table top first I would want to know why the boards came apart in the first place. Look under the top to see if the top was screwed to the frame or apron in such a way as to prevent the top from expanding and contracting with the change in humidity. If that is the case your repairs will eventually fail.

As far as re-gluing the boards, I'd run the edge of the boards over the jointer to cut away the tongue and grove then put Tite Bond II glue on the boards and use pipe and or belt clamps to pull it together. I have repaired 4' round tables this way. On one table the top had failed because there were lag bolts holding the top to the frame preventing the top from expanding and contrasting.

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post #9 of 27 (permalink) Old 03-20-2016, 06:23 AM Thread Starter
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Thanks for all of the suggestions and comments. Let me reiterate that the only power tool involved was a router with a straight bit. I don't have a track saw, jointer, or table saw. Only the width of a tongue was routed off of each of two boards. When I did a dry fit, it wasn't perfect, but it was good.

It's not important for me to go back and do any more work on this table. It's serving as a learning experience so that I can hopefully understand what I'm doing when it does matter.

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post #10 of 27 (permalink) Old 03-20-2016, 06:33 AM
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A couple of possibilities; first, is the clamp actually straight - do you have a true straight edge for checking it
Second, it is possible that the clamp flexed in the middle when you applied pressure to the clamping mechanism.
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