WET vs. DRY
A basic decision that must be considered is whether the material should be processed in a wet or a dry machine.  Wet and dry machines both process the material in the same way; wet machines simply add coolant that is sprayed on the part as it is processed. 

Dry Machines are often the first choice because they are generally less expensive to purchase and often have a longer life.  However, there are numerous advantages to processing materials on a wet machine. 

Wet Machines include a filter unit that also pumps the coolant on the part, and usually include a drying unit that removes the coolant from the part as it leaves the machine.

 Several advantages of a Wet Machine are:
 • A significant factor when choosing wet versus dry is the possibility of fires when a variety of metals will be processed on the same machine.  Some metal dust (such as aluminum) is very flammable, and in a dry machine this dust can be ignited by the spark created when running steel.  Timesavers recommends the use of a wet machine when a single machine will be used to process different metals.
• When processing dry, heat buildup due to friction of the abrasive belt on the work piece can cause unwanted warping, particularly on thin materials.  A wet machine virtually eliminates this possibility.
• Wet processing improves abrasive belt life due to reduced friction, heat and loading that occurs when grinding dry. 
• Wet processing usually provides a finer finish (a lower the RMA) when same grit belts are used to process wet versus dry.
• Parts processed on a wet machine exit clean and dry where-as a dry machine sometimes leaves residual dust on parts.
• A dry machine requires dust collection which means the dry system will have two foot-prints (one for the grinder, one for the dust collector), while a wet machine usually has one footprint.
• Should you choose to process dry, Timesavers recommends the use of a Wet Dust Collector attached to the dust hood/s of the sander.  Wet dust collectors capture metal grinding dust in a reservoir that must be cleaned regularly.
• Wet machines do cost more and require more maintenance to achieve these advantages however in most cases the positives outweigh the negatives.