•OK, here we go again. Since I'm pretty long-winded on certain subjects, I ran out of space in the last issue, so I'm hoping to cram the rest of my paint and body ramblings into the precious space allotted to me this month. As you'll recall, we ended by going over the different types of spray equipment common in the auto painting end of refinishing. Now we'll continue by spending a bit of time talking about spray gun operation, spraying technique, and gun and equipment maintenance.
Air Tool Maintenance Now that we've gotten a look at the basic tools of the trade, seen their most important components, and explained how they operate, it's only logical to touch base on the techniques of using and maintaining them. The spray equipment you've chosen-be it conventional or HVLP in design, will give you excellent results if used and maintained properly. Now, as you're all well aware, we can talk about how to use and take care of your tools 'til we're blue in the face. But there's nothing like hands-on experience to get these things to stick in your mind. So grab a couple of the more frequently used air tools you've added to your arsenal (the DA sander, the long board sander, and the 5-inch grinder) and keep them handy as we go along.
The first air tools to see duty in the body working process are more often than not the grinder and the dual-action sander. Most operations require that the existing finish be removed from the vehicle surface before continuing on with the repair. Sometimes it's a couple of layers of paint and primer, there may even be a layer of filler to contend with as well. The grinder and DA are actually quite simple tools. They're basically air-powered motors with hand grips and right-angle shafts to which a backing pad and disc are attached.
A trigger actuates a valve, allowing compressed air to flow through the tool. When it's depressed, the compressed air passes through a passageway to a chamber that houses what can be best described as a miniature "turbine." The turbine (or motor) is a machined disc that has a number of slots milled into its outer edge. Small vanes or blades usually made of a rigid fibrous material are fit into these slots to form a sort of paddle wheel, or what looks like the type of blade you'd see in a jet engine.
The compressed air flows through the inlet of the DA, or grinder's air passage, into one side of the chamber that houses this turbine-type blade and, in order to escape, has to flow past the blades. The pressure and volume of air passing through the chamber spins the blade that, in turn, spins the shaft holding the backing pad and grinding or sanding disc. As with anything that spins at high rpm, proper lubrication is a must. As you're aware, bearings or bushings that surround a spinning shaft won't last long if soiled by contaminants or with little or no lubrication.
The same holds true with your long-board sander. The long-board is primarily used for sanding large, flat expanses of body filler and it operates a bit differently than the other sanders. It uses an air-actuated piston (or pistons) to achieve its back-and-forth movement, and though it doesn't use a spinning blade-type motor, it requires regular lubrication even more than circular-type sanders.