jointing bowed timber

memzey · 12 Sep 2016

Yes and surely after the first pass or two you've made enough of a flat to reference off to make the rest much easier?

JakeS · 12 Sep 2016

Jacob":1ixs5q60 said:
It usually tends to balance itself roughly in the middle. You just have to hold it down in that position as you pass it over the cutters.

Out of interest, what is the particular advantage to starting it convex-down as opposed to concave-down - just that it's easier to balance the board and find the right 'flat' to plane, where starting concave-down would potentially make inefficient use of the board if the bend is all up one end?

It seems to me that - presuming you wanted to plane with concavity down for stability reasons - the only advantage that the 'dropping on' method described above has over just using the planer normally with the concavity down is that you can adjust how much you plane off each end; so if you have a mostly-straight board with a kink right at the end you can plane that kink down in particular rather than making a long, thin wedge out of the straighter bit.

In cases where one side is significantly more bent than the other I generally manage that fine (concavity down) by planing normally from the end to the point where the cutter no longer engages, lifting the timber up a bit - under the guard - by pivoting off the end of the table (which seems to me inherently less dangerous than dropping on, correct me if I'm wrong!) and pulling back over the cutter for another pass on that end. Repeat as many times as necessary to balance one end with the other, then plane full-length as normal.

(Instinct suggests to me that there's no reason you shouldn't be able to reliably plane boards up to twice the length of your planer bed, although I'd have to think about it more to be sure!)

Jacob · 12 Sep 2016

Same as I said in earlier post:
...given a regularly bent and/or twisted board (as most of them are) then the middle of the board will be closely parallel to the best possible flat face you can get out of it, so if you start at the middle you are on the right tracks.

i.e. you are establishing the flat face from the start and each pass extends it. You can refine this by looking at the areas un-planed - there should be shallow triangles at each end (with an evenly bent and twisted board) and they should be equal but opposite. You can adjust your handling to make them equal, if they've been drifting off. The last pass should remove two equal triangles from the ends

And also:.....there's another advantage with this: you are removing waste from the middle of the board and it's possible that when you thickness it it will be too thin in the middle but full depth at the ends. But for some purposes this is fine - you can joint the ends but the back (with saw marks) will be out of sight e.g. under a table top or inside a sash window chassis.
This means it's also a technique for hand planing - if you don't want the ends of the board to be too thin after thicknessing

It's not ideal every time but often it's quite useful.