If you are investing in a power sander, a random-orbit sander is probably the best choice for most common sanding jobs around the home. There is little point buying a selection of different sanders when hiring a specialised sander for the day is so cheap. A random-orbit sander will cope well with most tasks, are generally fairly cheap to buy and easy to use.
Choosing A Sander
When buying a random-orbit sander you should, as with any power tool, buy the best quality that your budget allows. At the very least the sander should have a 125mm sanding pad (preferably with Touch and Close fastenings), a locking switch for continuous operation, and some way to extract dust (either a built-in dust bag or vacuum attachment). You will almost certainly have a few sanding discs included with a new sander, but it is also worth buying a selection of different grades so you know you have them when needed.
Choosing Sanding Discs
Sanding discs for random-orbit sanders are usually made of aluminium oxide grit, bonded to a strong but flexible backing fabric. If the sander has a built-in dust extraction system, the sanding pad and discs will have holes in them (to allow extraction through the pad). Make sure that any replacement discs you buy have holes and that they match up with those on the pad. Sanding discs are available in a variety of grades.
Course to medium grades are for removing a lot of material quickly, whilst fine or extra fine grades are for finishing off a surface. Depending on the brand, the discs might be labelled as coarse, fine, etc, or they may have a numbering system. In almost all cases, the lower the number, the coarser the grit (180 would be a typical coarse disc and 400 a fine disc).
How to use the Sander
Random-orbit sanders are designed to leave as few scratch marks as possible, but you still need to make sure you are using the correct grade disc for the job in hand. It is almost impossible to completely avoid scratch marks when using a coarse abrasive disc.
1. Choose a disc of the grade required for the job and carefully attach it to the sanding pad. Make sure that the holes in the dics (if any) line up with the holes in the pad. Press the disc firmly and evenly onto the pad, making sure it is attached across the entire surface.
2. If the sander has a dust bag, attach this now. The dust bag on this type of sander will usually have a elasticated opening that fits over a lip around the exhaust pipe on the sander. If it uses a vacuum extraction system, attach the hose using the supplied adapter and switch the vacuum cleaner on.
3. Holding the sanding disc flat against the surface of the material, switch the sander on and start to move the sander backwards and forwards. Keep the pressure even and keep your strokes slow and steady. Don’t be tempted to move the sander in a circular motion as this reduces the effectiveness of the disc.
4. For jobs such as removing paint from a door, start with a coarse disc until the paint has been removed and then switch to a fine disc to finish the surface. If you are working on something like the bottom of a door or any piece of timber that will be hidden from sight, the coarse disc is all you need to use. For surfaces that need to be very flat (a table top for example), it is best to gradually change disc grades, passing over the surface with each grade until you can finish with extra fine.