Our tip this month relates to the refitting of used Bevel Gear sets on gear cutting machines. Each set of bevel gears that are made by a reputable manufacturer are marked with a "mating distance" and mating teeth are marked. It is always proper to replace both (all) gears in a given set in as much as these gears have been manufactured to mate. Replacing just one gear in a set means that you must depend on the action of the machine operation to "wear in" these gears and this usually results in a noisy set of gears. When refitting used bevel gears you must consider the manufacturer's "mating distance" as only a guide because the wear on the gears will have probably changed the distance. You should always change the fitting washers to set the backlash between the bevel gears to the machine manufacturer's recommended setting. When you change the fitting washers it is always a good idea to check for proper rolling contact between the gears. Sometimes, in attempting to set the backlash, one gear is moved so far out of position that the contact pattern between the bevel gears is lost. If this is the case, change the fitting washer sizes on both gears to bring them into proper mesh while maintaining the proper backlash.