Far from me to buck a trend, I concur with the consensus recommending the
#4. It's the one I most often reach for in just about any circumstances.
Using a plane isn't rocket science and really doesn't have a huge learning
curve. However, setting it up is a somewhat different story. Still not
rocket science but make you adjustments and test them on scrap before you
take on your panel.
For what you are talking about you will probably want the throat closed to
it's maximum and the blade set for taking the very finest of shavings off.
Don't get greedy and try to do it in one pass. Attack the surface with the
grain but with the plane at a slight angle to the direction of travel. This
will give you a cleaner slicing cut and help avoid chatter. Don't bear down
on the plane, let it do it's thing mostly by weight. You're not trying to
remove a lot of material here, just some raised lines.
When doing a panel you will probably find the hardest thing is getting the
blade parallel to the sole of the plane so don't test you adjustments on the
edge of a piece of stock do it on the face so you are taking full width
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