A dual action sander is a versatile tool that is often taken for granted in most applications and operations. There is sometimes a misconception that the operator does not have to be trained since it is a relatively simple tool to operate. On the contrary, DA sanding should be considered complex. It is a manual operation where the operator has to rely on his or her ability to remove surface defects and produce a consistent finish (defect free) at high production line rates. As with any sanding or finishing operation, all aspects of the application are important. The DA sander itself, the air supply, air hose, back-up pad and the abrasive play important roles. Any one of these alone can cause a defect to the workpiece.
Here are suggestions and recommendations to assist in eliminating common problems.
Startup check list
Before any sanding operation, first run through this check list.
1. Examine the sander prior to attaching to the airline. The DA sander should not be operated if any parts are missing from it i.e. muffler assembly, which will cause the sander to operate improperly.
2. Examine the back-up pad for damage. If the foam is separating from the pad face, is torn or adhesive remains on the vinyl face, the pad should be replaced immediately. All of these issues can and will cause surface defects because the abrasive disc is unable to sand flat and evenly on the workpiece surface.
3. Check air pressure at the regulator/filter. The sander will not operate efficiently unless the air pressure at the tool is 90 PSI while under load. Never operate the sander at higher than recommended PSI by the manufacturer, because it will cause premature tool wear.
4. Examine the air hose. If there are tears or if the connections are loose, the hose should be replaced. When damaged or broken, a serious injury could result. Hose length should be as short as possible and not to exceed 20 feet. For every additional 20 feet of hose length the air pressure drops by approximately 50 percent. Do not use a coupler to increase hose length, each coupler equals to an additional 15 inches of hose length, thereby reducing pressure.
5. When the sander is connected to the air line, check for leaks in the hose and coupler/plug. Air supply is critical to the performance of the sander. Without proper air pressure and volume (SCFM) the sander will create surface defects.
6. Make sure that the sander has the proper orbit for the operation/process being conducted. There are two orbits that are commonly used: 3/16 inch for general sanding and 3/32 inch for producing fine finishes. The orbit and RPMs can be found on either the sander’s lever or housing.
Basic sanding tips
Once you start sanding, follow these tips for better results.
1. Start on the workpiece. This will eliminate the sander from digging into the surface.
2. Stop off. Eliminates the possibility of the sander walking across the surface causing wild scratches and allows the operator total control of the sander.
3. Do not sand at an angle to the workpiece. Sanding at an angle will cause gouges that are difficult to remove.
4. Always keep the sander flat on the workpiece surface. This will eliminate producing an irregular surface finish.
5. Avoid excessive pressure. Let the sander do the work, apply light to moderate pressure for consistent finish and removal rates.
6. Use an overlapping sanding motion with the grain of the wood. Sanding in only one area will change the finish of the wood and result in a change of appearance once the wood is finished. Sand the entire surface evenly to prevent blotching or spotting.
7. Use the correct grit size. Use 80 grit for rough removal of wood, plastic, paint, filler, putty. Use 100 – 150 grit for breaking edges and general clean-up or major repair. Use 150 – 220 grit for final inspection, touch-up and minor repairs. Use 180 – 320 grit for washcoat and sealer sanding. DA sanders create a finish that is approximately one to two grits finer than a sanding belt finish. Example: 220 grit belt = 50 or 180 grit disc.
8. Maintain the sander. Use an automatic lubricator to supply the correct weight and amount of air motor oil if environment permits. If it does not then manually lubricate tool (2-3 drops throughout the day) directly into the air inlet i.e. at start-up, morning break, lunch, afternoon break, end of shift – the muffler assembly should be removed during this process so that the oil will not clog it. This should be done in an enclosed area so that the exhausted air will not recirculate into the plant and cause finishing issues. Clean or replace exhaust muffler elements as needed and never operate a tool without one.
9. Use the proper air hose. Never use a coiled hose if possible as it restricts air more than a straight hose and often is longer than required. Hose should be as short as possible and never exceed 20 feet.
10. Couplers and plugs. Always use maximum flow couplers and plugs; they are 35 percent larger in diameter then standard ones and allow optimum air flow to the tool.
Effects of a back-up pad on finish
A back-up pad has a direct relationship to the finish being produced, removal rate and abrasive life; it is an extension of the tool/ sander. There is a misconception that as long as the disc adheres to it there is nothing wrong with it. This is completely incorrect.
There are two commonly used back-up pads: low profile and tapered. Each one is available for either PSA or hook-and-loop discs. When the outer edge of the back-up pad is damaged (i.e. separates from the foam, foam is torn or adhesive remains on the vinyl face), it should be replaced immediately. All of these issues can and will cause surface defects because the abrasive disc is unable to sand flat and evenly on the workpiece surface. Always keep the face of the back-up pad clean.
Avoiding swirl marks
Swirl marks are also called jitter marks, curly cues, pig tails, fish tails, fish hooks, half-moons, or grit marks. They are caused by a number of factors, including inadequate air flow, damaged back-up pad, back-up pad too soft or too hard for application and grit size, incorrect operator technique, sanding too fast in an overlapping motion, wrong sandpaper and/or grit size, or a poorly maintained sander.
The perfect air hose
Choosing the right house will improve DA sander performance. The ideal hose has an inner diameter of ⅜ inch. As mentioned previously, the hose should be as short as possible.
Air hose can be either rubber or synthetic, and both have advantages. Rubber hoses are durable and wear resistant. Synthetic hoses are light weight, flexible, and ergonomic.
Maintaining a DA sander
Proper maintenance will go a long way to getting the most out of your DA sander. Key to preventing damage is to provide a good clean air supply. Reduce or eliminate condensation and moisture from the air supply. Prevent debris from entering the air motor. Do not remove exhaust mufflers/elements to use as a blow-off tool. Lubricate the air motor. Clean or replace exhaust muffler elements as needed.
When using the tool with accessories or related products, use only as specified by the tool manufacturer. This includes adhering to specified maximum operating air pressure and maximum operating RPMs.
Lubricate gears, sleeves, bearings and sliders as specified by the manufacturer. This information is usually found in technical support literature provided by the manufacturer.
Avoiding air supply restrictions
It is important to prevent and eliminate air supply restrictions to achieve top performance. Some common causes of restrictions include:
• The air supply hose is too long (>20 feet) or more than one coupler.
• The inside diameter of the hose is too small for tool PSI/SCFM requirements.
• The air connections or fittings have an inside diameter that is too small.
• There are too many air connections or fittings being used.
• If an inline filter is being used, the unit may be too small or the filter element may be plugged.
• If an inline regulator is being used, the unit may be too small, not adjusted properly or defective.
• The air supply hose, air fitting, air tool inlet or air tool exhaust may be plugged.
• If the air tool has a speed regulator, it may be closed.
• Insufficient air supply or drop line diameter too small for air tool PSI/SCFM requirements.
• Improper coupler/plug, should be maximum flow to eliminate air restriction to tool.
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