Slow learning, hard lessons.

Rennie Heuer

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Some things I never seem to learn and continue to make the same mistake over and over. I can't be alone in this, so I figured I might start the topic and see if anyone else suffers from the same malady.

For me, the one lesson I refuse to learn is that random orbit sanders are not meant to flatten, they are meant to smooth. I don't know how many times I have used a ROS on narrow parts or sanded past the end of a board only to find out that the edges are no longer in the same plane as the middle of the part or, in sanding an end, it is no longer a right angle but an arc. All that work at the jointer, planer, table saw to keep the stock flat and square goes right out the window after only a few seconds of abuse from the ROS.

It seems the ROS, with its convenient hook and loop paper has just too soft a pad to insure that anything you sand will stay flat. Maybe someday I will learn.
 
I don't own any, but from what I know, ROS are meant to remove material fast leaving the surface smooth as you mention, but not flat. That's why they are widely used in car repairs, they allow to remove the poliester filler resin and or paint following the curvature of the metal sheet and leave it smooth. Obviously if you get close to an edge they eat it before you can even notice.

If I wanted to leave a surface flat, I would use a belt sander, and a normal orbital one just before finishing, but again I'm no expert.
 
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