It's an ironic fact that some of the highest-quality table saws, typically made with cast iron for the table surfaces, are the must susceptible to rust. Cast iron is the gold-standard for large stationary table saws, where the heavy weight lends a stability that isn't possible with the lighter-weight cast-aluminum or pressed aluminum used for portable table saws. Cast iron makes for an extremely durable saw, but its drawback is that it is prone to rust, especially in high-humidity climates, such as coastal regions.
This can be especially problematic with saws that are used infrequently and aren't regularly maintained. If your cast-iron table saw hasn't been used for a few years and has accumulated a pretty substantial amount of rust on the table, you can usually remove the rust and prevent it from coming back. There are dozens of recommended methods for doing this, as sometimes it seems that just about every woodworker has a method they swear by.
Assessing the Situation
The first step is to assess the situation. If the rust is relatively light and superficial, it won't take much to clean up the problem. However, if the rust has been accumulating for a number of years and appears to be substantial and deep, the saw's table is probably too damaged to return it to its former glory. The saw should still be usable, but its operation won't be as smooth and precise as it once was. It may still be perfectly suitable for cutting framing lumber or large panels, but it may no longer be idea as a tool for fine woodworking.
No matter how deep the rust appears to be, you won't know how well it can be restored until you try. Here are several tried-and-true methods for removing rust from a table saw.
Sandpaper or Steel Wool?
One of the most common methods for removing rust from a table saw is one that you should absolutely NOT use: ordinary sandpaper. Under no circumstances should you attack the table of your saw with any kind of sandpaper, either with a power sander or by using hand-held sandpaper. Some people think that steel wool or a very fine sandpaper, such an 800- or 1500-grit wet-dry sandpaper can be used to remove rust and polish a table saw, but steel wool or fine sandpaper always leaves fine scratches in the metal that will make it susceptible to collecting moisture, causing more rust in the future.
Instead, use a synthetic scrub pad in conjunction with some kind of oil to scour the table of the saw. A Scotchbrite or similar type of synthetic fiber scrub pad is ideal.
Mineral Oil or WD-40
A synthetic fiber scouring pad provides enough abrasion to remove rust from cast-iron without scratching the metal, but some kind of lubricant is required. Mineral oil is a perfect choice. Apply a sufficient amount of oil to the table before you begin to scrub, but make sure not to be excessive, since you'll need to wipe off the oil when the scrubbing is done.
Scrub the metal table thoroughly using both circular action and back-and-forth motions until all rust has been eliminated. Then, wipe away all traces of oil with a clean cloths until the metal table is completely dry. The metal will retain an invisible layer of oil that is dry to the touch but which seals the metal against the moisture that causes rust.
For heavier rust, you may be able to use your random orbital sander to help with the scrubbing. Place the base of the sander on top of the scrubbing pad and get to work.
Some people like use WD-40 instead of mineral oil, which works fine, although it evaporates more quickly than mineral oil. Should you choose to use WD-40, apply it often and to the entire saw table to keep it lubricated until you've finished scrubbing. Because this oil evaporates completely, rust may return somewhat faster with the WD-40 treatment.
A completely different idea that has some merit for extremely rusted cast iron tables is to use naval jelly. You'll need to follow the instructions on the naval jelly to the letter, particularly when it comes to rust removal, so as to avoid pitting the cast iron. Naval jelly is quite aggressive for rust removal, and it needs to be removed properly to stop the cleaning action.
Protecting Against More Rust
Once the rust is removed, take steps to ensure that the rust won't return. There are a number of commercial products that not only protect the table from rust but also lubricate the table to make work pieces slide across the table better when cutting. Boeshield T-9 and Slipit are popular products, available online or at most retailers selling fine woodworking supplies.
Paste waxes also work well for protecting and lubricating, but avoid the temptation to use car paste waxes. These formulations typically contain silicone, which will plug up wood pores and cause issues with finishing the wood. Instead, try Johnson's Paste Wax, of the type which is formulated for the floor. Apply liberally, wait until it is nearly dry and then wipe the table down to remove any excess and polish the surfaces.
Plain old distilled vinegar can be quite useful as a rust inhibitor. After the majority of the rust is removed using your method of choice above, wipe down the entire table with a liberal amount of vinegar. Allow it to dry and then apply your final protectant/lubricant. The acidity of the vinegar should help clean up any last little bit of rust that you may have missed, and should also impede the future development of more rust.
Alternatives to Cast Iron
Recent innovations in table saw design have led to the use of other materials for the table surfaces on stationary table saws. At the upper end of the market, there are now large pro-grade stationary saws that use granite tables, which are completely immune to rusting.
Some woodworkers cover the table of the saw with a layer of finish-grade plywood or MDF to create a smooth, solid surface. This can be a good choice for improving a saw that has a cheaper aluminum or stamped steel table, or when a cast-iron table saw has been too badly damaged to be fully restored.