Edge joining long boards


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21 Oct 2020
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Bridgwater, Somerset
I have 2 pieces of 20mm x 150mm pine that is planed all round from Wickes. They are 1500mm long.

The pieces have cupped slightly (about 1mm gap when a ruler is placed acwhen I left them out in the workshop to acclimatise and I want to join them together to make a wider board.

Should I

a) square up both pieces using my jointer plane and then glue and clamp them

b) square up just the joining edges and then glue and clamp them and then square up the wider board?

When it comes to joining the boards I could either just glue them or biscuit joint and glue them. What would people recommend?

Personally I face and edge both pieces, join them then dimension to final size. I don’t use biscuits (haven’t got a biscuit jointer so don’t know what I’m missing!). I haven’t got much science behind it other than I find having the two pieces square makes it easier to get good alignment and so makes less work once they’re glued up
I think, if you are only joining two lengths, you will either end up with a panel with is (a) fully cupped, or (b) an "S" curve/wriggle. The final possibility depending on how the edges are planed is a flattened "W" or "M" profile.

More practically - I would flatten and square the edges before gluing. This probably gives the best chance of getting a flat board. I would use biscuits if you can to ensure when joined the boards remain aligned.

To machine plane the joined boards you would need a machine with a 300mm capacity - fairly large and not a normal piece of hobby kit. Lunch box thicknesser, if you have one, may have sufficient capacity.
I would have thought the chance of telegraphing from the biscuits would likely be a possibility.
I would cut into 4 75mm boards and joint otherwise you will get a very wavy top.
Hi, To minimise the effect of cupping you could rip the boards into narrower strips,alternate the heart as suggested and glue back together. They could be rub jointed to have the joints disappear if you wished.
I've followed custards guide and it's excellent, usually use my no7 plane.

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