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Re: I'd suggest an experiment to put your mind at

Sgian Dubh
"A question, have you ever seen that biscuit swelling issue in person? I never have and I used the biscuits by the thousands in business."
You weren't asking me that question Dick, but I can report seeing oval depressions in solid wood panel glue-ups that reveal the position of biscuits. Similarly, I've witnessed a furrow along the joint line where the joint has sometimes included the addition of a slit feather (aka loose tongue). The fault was clearly visible on horizontal panels, but not so easily spotted on vertical panels, which is largely to do with the way light reflects off horizontal and vertical flat surfaces.

This phenomenon occurs when the maker hurries the job, i.e., panel glued up first thing in the morning, and prepped and polished by the end of the working day. Yes, it happens; I've seen it in workshops under pressure. The cure is to leave as much time as possible between glue-up and the prepping and finishing to allow the water swollen areas to shrink down again, whether it is a plain edge joint or one reinforced with biscuits, dominoes, slit feathers, etc. Two or three days is good, and a week is better still.

Interestingly perhaps, I can't recall seeing this fault where solid wood lipping has been attached to a veneered board with the lipping either just glued on or with reinforcements or alignment aids, e.g., a table top, although I can envisage it occurring. Perhaps my memory is failing me, but if there had been some sort of local swelling still evident at prep time, then it's possible the prep work could have removed the veneer locally to reveal the ground underneath.

The link to the article provided by Alan discusses the same fault, its possible causes and strategies for eliminating it. Slainte.

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