my question concerns a procedure for wood preparation for panel gluing. I have, say 3 boards which I want to glue to the panel. They are not twisted, but they have slight cup. Shall I plane them straight before the gluing together or after the gluing? The boards are currently the same thickness, if I plane them separately before to make them straight, I might finish with boards of different thickness. If I glue them first and then plane, I might plane much more if the total panel cup goes the bad way.
what is the best way?
I think the generally accepted procedure is to plane one side flat on all the pieces then plane them all to the dimension of the thinnest one. Glue them together so that one side is as flat as possible with all the slight steps concentrated to one side of the panel. After they dry, plane flat on both sides.
Some people flip the direction of the end grain on the middle board so the cupping direction is alternated, but that can cause problems of its own (you generally can’t plane the panel all in one direction due to reverse grain in adjacent boards)
I don’t like to do this, for small panels I go for the best grain and color match and plan a holding method into the piece to keep the panel flat.
D. I am no expert on this but I would think it better to plane the boards flat and straight before the glue up. I think you would compound the problem by trying to glue them up with a cup in each board. That’s just my humble opinion..
Here’s another thought… What is causing the cup? Have the boards been laying on the same face and the affects of moisture and drying on one side caused this? If so you might consider turning them over and allowing the cup to normalize. I’ve done this and in some cases the boards have come back completely flat again. I store my lumber vertically to prevent this.
You will need at least one trued face in order to edge joint the boards. Gluing up without any preparation would be unwise.
Whether you get all the boards four square before gluing the panel is a question of some debate; when I do a panel glue-up I true one face and both edges, but leave the other face as it is (or roughly skim it if it’s really out of shape). The way I see it, even the most careful panel glue-up will have slight misalignment of parts, so If I true both faces I’m only jeopardising the final possible thickness of the panel.
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