Chuck and Allen you are both correct. If you look down on the top you will see three breadboard sections which will hold the entire top together. I made the boards just over 1" thick. The rail that holds the legs together is 1 3/8 inch thick and will have a support attached in the middle to support the top. I think I could use less than an inch for the tenon but one inch seemed like a good even figure. The breadboards are 3 1/4" on the outer ends and 5 1/4" on the middle. I started out trying to get 1 3/8" thickness for the top but had to make it slightly thinner in order to clean up on side. I don't purchase first quality lumber so I often find myself making do. If I get an agreement on the 1" I will go with that. You know how it is you just want someone else who makes furniture to give you some opinions before you take that last step. Thanks for the help guys, wouldn't do it without your help. Lorraine
Merry Christmas
Lorraine,
I'm not stalling on answering your question, I have been hoping that a few of the guys on this site that really KNOW how to make furniture would chime in. I'll give you my take and hopefully someone with more experience will validate my advice or offer a compromise.
If I were building that table using the two laminated top panels with a breadboard center then I would make the breadboard tenons 1 inch long, 3/8 thick.
If your current design will support the center at more than a single point then it should be fine. I just don't want to see the table fail if/when someone sits on the edge around the center of the table. The breadboard joint does NOT add much resistance to a bending force.
I can think of two different ways to beef up the support for this design.
1. Modify the base design and use two rails - one on each side - to support the top from underneath. These rails would run between the trestle tops and could be M&T into the trestle top. The purpose of the side rails is NOT to reduce racking but to provide a means of supporting the vertical load at the weak center breadboard area. The rails could be two inches wide and could be set in 10-12 inches from the sides to keep them from being prominent.
2. A second idea would be to add a cross piece on top of the large 1 3/8 thick rail that goes between your trestle ends. This could use a simple edgeways cross halving joint. The cross piece doesn't need to be thick and could taper to the ends (toward the outside of the table). The top member of the joint could extend far enough toward each side to provide support for the weak breadboard center. I actually like this approach. It's very simple to construct and would allow your center stretcher to carry the load. I wish I was capable of sketching these ideas but am CAD-challenged. If your planned 1 3/8 inch thick rail is located too low to work than simply add an additional rail for this option.
The whole point of my response is just to warn you that the center joints on that table are subject to failure if you don't provide additional support from underneath. I don't like the idea of just a single point support in the center of the table.
I'm hoping someone a little smarter than me will respond. Does anyone else have any ideas?
Keep in mind that it is a little bit tough to recommend a solution without seeing your base design.
Chuck