Such a great discussion about the PC sander bearings, I thought I’d ask you all about my odd problem with a Bosch 3272 DVS (6″ ROS). I’ve had it for years and it has given me great service, replaced the pad once or twice. Now it has developed a very odd behavior: it won’t start unless I turn it upside down and tap it on the bench while squeezing the trigger. (Seriously!) It acts as if there is a loose connection or something, but I have taken it apart several times and can’t find anything obvious. I replaced the switch, no effect. Checked the brushes, plenty left. Can’t figure out how to remove the variable-speed unit to check that.
Any ideas? Is it just worn out? (Possible, it must have a lot of hours on it by now.)
“Everything should be made as simple as possible, but no simpler.” A. Einstein
Replies
The symptoms suggest that there is a brush problem. The brushes, even if they are not worn out, could be sticking in their holders, remove the brushes and clean up the inside of the holders with a fine file, fine sandpaper, or Scotchbrite and lightly clean up the sides of the brushes. Most brushes have a wear line cast in them, if the brush is worn close to or past the line, the brush may need to be replaced even if it still looks long enough.
Check that the brush springs haven't gone soft or cracked and that the braided copper leads that go to the brush, if they're used, are firmly embedded in both the brush and the copper contact at the other end.
If the commutator surface is pitted and burned, clean it off with a fine file or abrasive. Take a close look at the connections between the wires from the armature coils and the commutator strips, if a connection is broken, or one commutator segment is damaged, the motor will have a dead spot, where it won't start if the bad segment is under the brushes.
Check that the brush springs haven't gone soft or cracked and that the braided copper leads that go to the brush, if they're used, are firmly embedded in both the brush and the copper contact at the other end.
Variable speed is a problematic thing. Much more liable to give problems than a simple off, on switch. Learned that from my days as a service tech for tools and machines.
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