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Dining table failure12/20
I recently made a trestle table for a client who supplied the lumber. Top dimensions are 40x83x1.25. The breadboard ends were attached with tenon, glued. A few months after delivery a crack developed in the end of the glued up panel not at a joint. I checked some residual lumber and the MC was 12%+, something I know I should have checked prior, hindsite, assume, etc. etc. My Bad! My question is could the split have been avoided or caused by the gluing of the breadboard ends?
The breadboard end should only be glued in the middle. The outside tenons on the top should have elongated holes drilled for pegging the breadboard to the top. Drawboring the peg holes, that is drilling the tenon hole slightly closer to the shoulder than the holes in the breadboard mortice draws everything up tight. With a breadboard edge there will be noticeable seasonal variations as far as whether or not the the top's edges are aligned with the breadboard's ends.
There is certainly an incompatibility issue between the glued breadboard, air dried lumber, and (I assume) the climate controlled environment that the table lives in. Aside from yourself as the craftsperson, the glued breadboard should get the lion's share of the blame, as a traditional breadboard would not have resulted in a crack under the same circumstances. I will say that a glued breadboard does not necessarily result in failure, but it can't be left to luck. You said it: your bad.
Sounds like a classic cross grain situation compounded with bad woodworking. Hind "site" indeed.
Ouch! Uhhh thanks guys. Truth burns sometimes. Thanks for your help.
I hope you learn from your mistake. You do realize that the customer views you as the expert. You should take it seriously and become that expert. If you don't, then you are ripping people off. I don't understand why so many guys think that they can just open up a shop and do this stuff on their own, with little to no knowledge of the trade. Its disrespectful.
I had the exact thing happen with a very large office desk. The lumber was sourced from a reputable yard and was kept in doors while in my possession. 9 months later after delivery the end cracked at the glue joint for about 1" then pulled a split into the adjoining board. The customer told me that the area that split had "putty" in the joint. The glue was not old (Titebond 3). This clued me in that the board had more moisture in it at on end and caused the failure. The office was also very very hot and dry in the winter. I replaced the table top at my cost. All I can figure is that it may have been exposed to weather before it was shipped to my shop.
Bryant, Did you also have fully glued bread board ends?
No I did not glue across the tenon in the bread board. It had a little glue in the center and was pinned. One in the center and two outside. The outer ones were driven through slots so they could move with expansion and contraction. The tenon of the top (which was hidden) was also cut shorter than the mortise length so it too could expand and contract. However I know another maker who did fully glue a breadboard and sure enough his table formed a split. A way around this can be a sliding dovetail bread board. It's a little tricky, but just requires some accurate router setup and a little hand fitting. I have seen it done successfully on some new and 18th cent. tables. Once in place you simply pin/nail/screw the center.
When lumber is dried, sometimes there are very small end splits...maybe a big split right at the end, which will be cut off, but the split actually goes further...hard to see with the eye. So, if you put that end (with the microscopic split) in a top, when the top does shrink, even a little bit, that existing microscopic crack will open. End coating of lumber before drying is widely practiced to eliminate this issue (mostly), but not everyone end coats before drying or uses enough coating material.
The outer ones were driven through slots so they could move with expansion and contraction. The tenon of the top (which was hidden) was also cut shorter than the mortise length so it too could expand and contract. -