Yes it needs to be wider indeed so it has sufficient long grain gluesurface. But that would rule out a new groove at almost the same spot.
Yep, I think this would just about do the trick: http://www.starrett.com/metrology/pr...ng-Tools/20-36
The 24" version would probably be marginally acceptable for woodworking, and only costs $1681.
One edge of the dovetail socket needs to be cut more (straightforward) and the other less. What if you convert to a half-dovetail by filling the part that needs to be cut less, leaving the edge square? Even if undercut it would not hold well because of short grain, but cut square it would be held tightly in place by the dovetail. You could orient the grain of the filler pieces crosswise, and just leave it several pieces to take care of crossgrain expansion. They would not even need to be glued to be strong.
That's a bold solution to affix a top! I think my proposal is similar to Brian's, but I can see things better than I can read them.
I would carefully rip the sliding dovetail part from the rails with a view to reuse them. The ripping will create a joint that is too tight as the dovetail will move lower within its housing. I would then screw the ripped dovetail pieces into the correct position. That might mean a few attempts at getting them screwed in the right spot and planing an edge of the dovetail as required. Once happy with the fit I'd then glue and screw the dovetails back onto the rails. Then fix the top on. Nobody would ever know!
Good luck! Hope my ramble made sense and sorry if it's just a copy of others tips.
For everyone who has not the slightes idea what we're talking about, here is a sketch, heavilly exagerated of course!.
SLdvt.jpg
Explanation: As you can see there is an error in the parallelity of the grooves and the sliding dovetails. If I could drop the top down onto the cabinet, then the fit would be fine. But because these are dovetail shapes, I have to slide it in from the front. Of course that is impossible in this configuration.
Last night while hanging around at the climbing gym, I thought about a possible solution.
SLdvt2.jpg
I cut up the crooked dovetail. The part above, near the letter B can remain in place. The error at this end is too small to worry about. The end below needs to be loose and it must be able to slide from side to side. So I can engage it when I start to slide the top onto the cabinet, and when I advance, it can slide back to its permanent location.
How I am going to fix it in place afterwards is another thing of course, and I still have to weigh up the various possibilities. It depends on how much meat I have in the top rail at this point.
How about rather than patching the groove, you laminate onto one or both sides of the tail as necessary (you could even square it up first to ease lamination/clamping). Then widen the groove the necessary amount to make it parallel to the other groove, and finally recut the tail accordingly.
Last edited by Noah Magnuson; 06-22-2017 at 7:50 AM.
I think at this point you should cut your losses and switch to metal tabletop fasteners and screw them in from underside and take this as a learning experience.
I'm not following some of the proposed solutions, so pardon me if I'm aping someone else's idea:
Could you cut one of the existing 'grooves' out to be rectangular cross section - keeping same depth, but say 75mm wide. Leave the dovetail of the carcass alone.
With the top upside down, invert the carcass and slide one dovetail into it's mating groove. The other dovetail will sit loosely and approximately centered in the new rectangular groove.
Now make several gibs (~25mm W. x ~100mm L.) with one edge matching the angle of the loose dovetail. Drop a gib into the open groove, engage the 'loose' dovetail, and screw it to the top. Repeat for the opposite side of the dovetail. Alternate installing gibs back and forth along the loose dovetail's sides - leaving enough gap between the gibs to allow seasonal expansion of the top ...???
Gibbed dovetail_1.jpg
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Edit: You could even do this to one side of the groove (just be sure to pick the correct side):
Gibbed dovetail.jpg
Last edited by Malcolm McLeod; 06-22-2017 at 9:19 AM. Reason: Gibbed on one side?
You all have great ideas. Now I have sleepless nights about which one to choose.
I managed to find some time to work on a solution. The problem is that the two grooves and the matching dovetails don't run parallel. That makes it impossible to slide the top in place. Some of the solutions have the same problem, it would fit nicely when done, but it would have an assembly problem.
So, I decided to cut of most of the dovetail. Only the last 10 cm was left in place. At that end the error is so small, that it doesn't really matter. Next I made two loose dovetails with tenons. These can be inserted in mortices cut into the top of the rail. But to be able to assemble the top I made these morices very sloppy, so the dovetail key can slide a bit from side to side. This makes it possible to slide the top in place.
Of course, now those two dovetail keys are pretty loose in their mortices and won't hold the top down. to fix that I will drawbore them. This also has the tendency of pulling the dovetail down and thus locking down hard. Of course now there will be two draw bore pins visible on the outside, but that is not a problem. I think that only adds to the magic of the piece
Here are the two loose dovetails and the piece that is still fixed. I have pulled the middle one out of its mortise, so you can admire my spotless joinery technique
IMG_3962.jpg
And this is how it would look in the finished piece. Of course those two holes will be filled with a wooden pin.
IMG_3963.jpg