Things You'll Need
New sandpaper belt
Belt sanders are the heavy artillery of your sanding arsenal, providing the kind of power and consistent movement that pad sanders, rotary sanders or hand-sanding just can't match. Belt sanders are harder to control than other sanders, and changing the sandpaper belt can be tricky if you aren't used to the tool. You will know it's time to change the belt when you can run your palm across the sandpaper (with the sander off, of course) and feel little resistance from the sandpaper.
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Unplug the sander. Take it to a workbench or other flat, elevated surface.
Locate the tension lever on the side of the sander, between the top and bottom spans of the sandpaper belt. Lay the sander on its side so the lever is facing you.
Pull the lever upward. The two wheels will move incrementally toward one another and lock there, causing the sandpaper belt to slacken on the wheels.
Slip the old sandpaper up off the side of the rollers. Slide the new sandpaper back on in the same fashion, making sure that the arrows on the back of the paper are pointed so the belt will rotate in a forward direction. (Think of the belt as the treads on an army tank.)
Push the tension lever back down to tighten the new belt in place. Plug in the sander and proceed with your project.
If you can't find a lever that releases the rollers that hold the sandpaper, you might have another style of sander that requires you to press the front wheel against the edge of a workbench or wall, physically forcing the wheel back until it locks into a non-tension mode. The tool is returned to tension mode by prying the wheel back into place with a flathead screwdriver.
Make sure the tool is off before you attempt to change the belt. Wear eye protection when using the sander.