Reply To: Stock prep and gluing up a panel
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Draw on a piece of paper a board with a cup – one side is cupped (concave) and the other side is bowed (convex). (I am not going to mention twist because it adds to the complexity and I am trying to keep my thoughts simple her. You will get the idea.) When you plane the board flat, you can radically change the actual dimension of the board. You will plane down to the bottom of the valley on the cupped side and down to the edges on the bowed side getting a fraction of the actual board side.
When watching Paul’s videos for the projects, he is already using planed square boards. Sure he gives them a quick planing to remove the snipe, but, with his plane being flat, he is not changing the squareness of the boards he is using by any significant amount.
I work with someone who gives meĀ boards 3/4 x 6 x 18 that he ocassionally receives as part of a project that he teaches. Genreally, they are pine and on ocassion he gets a piece of poplar. Anyway, beng new, I watched Paul’s videos, grabbed two boards and tried to make a dado. Then I tried to make dovetails. No surprise, gaps. I took the boards as is because they looked flat. Duhhhh!!!! I did not think much about it for the dados because they were relatively easy to make, the gaps were small and the edges of the slight bow and high point of the cup kept the board in place. I went to Home Depot, bought the more expensive select pine instead of premium pine, made the shooting board and felt comfortable with it. (I took the time to check for flat and square which started me thinking.) There is a huge difference betrween the select, premium and common board pine at Home Depot and you get what you pay for.
Dovetails were a different story with the wood I was being given. I was taking pains to markup square and cut square when I cut the tails. When I went to markup the pins, I thought I was okay except that I kept noticing that my pencil line for the thickness of the mating pieces were different from when I used a square. When finished, gaps on ends, gaps in middles, arghhh!
So I started to think about it. Out came the ruler. Ever so slight bows in the middle!!!!
Now I am needing to learn how to plane flat and sqaure. Out comes the pencil, paper and picture drawing, That leads me right back to the beginning of this post. That 3/4″ board when planed flat was no longer 3/4″ in actual dimension. It was much less. I will admit I am probably planing more than I need to at this point, but, I am learning by trial and error.
Now we come to the relevant point, The edge dimension is different which is acceptable and I can plane both boards almost to the same dimension which is fine. However, when I put the faces together, they are flat together. Now when I match plane the two boards, the offseting angles will give me an even edge when I go to glue up.
But, what if I did not plane the boards first before match planing? The planed agles will still be the same. The ridges at the glue joint will be slightly different depending upon the amount of cup for each board. However, this is not an issue (except for harness on a plane) since the laminated board will be planed down to the smaller of the two boards as if you planed them before gluing up.
So, in my humble (but lengthy) opinion, it might end up being “6 of 1 – half a dozen of the other.” But, when I plane two boards flat before glue up, I am also needing to plane to thetwp boards to theĀ same dimension. If I wait until after glue up, I still have to plane to flat, but, I don’t need to think about dimension unless I need to get to a specific dimension.
Edge: planing after glue up!!!