This article is from the Woodworking FAQ Collection 3, by multiple authors.
From: creagh@forestbear.Sun.COM (Creagh Yates)
Date: 14 Feb 90 23:58:23 GMT
In article <6@fedeva.UUCP> bill@fedeva.UUCP (Bill Daniels) writes:
>creagh@forestbear.Sun.COM (Creagh Yates) writes:
>>How do you straighten out a long bowed board on a tablesaw, prior to edge
>>jointing, so that you can rough cut widths narrow enough to joint?
>>If you think this is just a theoretical question, I can assure you it
>>has saved a lot of work on badly bowed boards.
>>Hint: The concept is similar to scribing.
>BIG ASSUMPTION FOR REST OF POSTING: By BOW I think of a curve in the long
>dimension, CUP is curve across the width, and TWIST being that all of the face
>of the board is not in this same plane. BOW comes in two varieties, one where
>the concave/convex is seem on the edge, and another where the concave/convex
>is seen on the face.
Bill, you have brought forth the exact type of response which I was hoping
for; one that would make people aware of the terms Bow, Cup and Twist, which
confuses the heck out of most people. Good job describing them all! Your
mentioning Bow in two varieties is also perfect, because it is a tough
concept to grasp. I think if edge bow as looking like a bow and arrow
bow. That is the kind of bow that the question was related to.
>I would first cut the board to rough length, maybe with (could it be) a handsaw.
>This should remove enough of the bow to make the piece manageable. Then (this
>is where CY and I may differ; I am open to enlightenment :-) with the
>concave edge down on the jointer bed make many passes to flatten one edge.
I completely agree, lumber should always be cut to rough lengths before
jointing, and a radial saw will do fine for that matter. However, there
have been a few times where the bow was so bad and I needed a piece 10'
or longer, that I used this trick.
Take a straightedge piece of plywood about six inches wide, you may have
to splice it together to get it long enough, just nail a patch over the
two peices. Then tack the plywood straightedge onto the bowed board so
that it hangs a couple of inches over the concave bowed edge.
This edge of straightedge along fence ________________________________________________________ Straightedge / _________Cupped edge of board______________________ / Tacked on top /_/__________________________________________________/__/ <--- / Board with cup on edge / /__________________________________________________/