On 1/30/2019 12:41 AM, Jerry Osage wrote:
On Tue, 29 Jan 2019 15:27:42 -0800 (PST), DerbyDad03
wrote:

I'm trying to flatten the
long twisted boards first and use the thinnest of the resulting boards as
my final thickness. Since one end keeps coming out screwed up, I'm simply
trying to determine what is causing the problem.

Are you shimming under the boards anywhere they are not touching the sled?
If one edge is not touching the sled I'd want a shim every 12".

At least, and depending on the thickness of the stock and the material,
perhaps will need far more than that to take any flexing out of the
workpiece itself as it goes through. Planers exert quite a _lot_ of
downward force and wood is an elastic material.

Also, with these little lunchbox planers, the construction on the bed
mounts/head simply may not be stout-enough to resist the wracking forces
when there is a significantly different side-to-side loading owing to
twisted material going through the planer. D-D may simply be deforming
the geometry of the planer itself in part because it isn't built
strongly enough for the task.

The plain planing (so to speak ) exercise will at least eliminate
that the head isn't aligned with the table when the forces are uniform
across the stock; after that is confirmed then he can move on to better
arrangments to hold the workpiece and checking for other issues.

But if his stock he's trying to straighten is 4/4 or less, it's going to
take a really solid support all along the length to keep it from just
bowing as it goes through...why I've rarely in 50 years done the
exercise for other than heavy stock--it's just too much bother given
there are better ways to rough prepare the material first or just use
better material from the git-go and find other uses for the specific
material. Unless it's a really exotic, high-priced or truly remarkable
in some other way, the result just is rarely worth the effort in my book.

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