When you want to get the best finish on your project, it comes down to the quality of the sanding. Sanding with a random orbital sander or orbital sander (without random pattern) is not complicated, but there are several things to consider in order to avoid common problems, and get the best possible finish. When sanding incorrectly, you can cause swirls, excess dust and other issues that will lead to an uneven or blotchy finish. On the other hand, if you use good technique and avoid the mistakes explored in this article, you’ll have a high-quality finish every time.
1. Avoid pushing down with too much pressure on the sander.
We all want to finish sanding faster, and get the best cut from the abrasives, so it can be tempting to press down harder with the sander. Intuitively, it seems like that could make the sanding process go more quickly. However, doing this can cause issues like swirls, cut-through, uneven sanding and other problems, such as excess heat and loading. When you use too much pressure, the sander has to do more work to perform its rotations, this means there will be more work for the motor and more friction on the surface of the workpiece. Both of these things lead to more heat. More heat can either cause the sander to shut off or potentially lead to pre-mature loading of your sheets or discs.
The rule of thumb for this is to let gravity, or the weight of the sander, and the abrasives, do the work. Each grit is designed to remove a certain amount of material, so if you need to remove more, use a coarser grit, rather than pressing harder. When sanding properly, the sander should move across the surface with ease, as if it were gliding.
2. Avoid sanding too fast, or too slowly.
Because sanding is often tedious, many people want to finish sooner by moving the sander very quickly on the workpiece. However, like most things where quality and attention to detail are important, moving the sander at a controlled and even pace across the surface will lead to the best results. It’s a bit of a “Goldilocks” issue – going too fast can lead to poor results, with sections not sanded enough or missed entirely, and going too slowly can lead to over-sanding or cut-through in some areas. But, finding that “just right” speed will mean a nice, even sanding job across the entire piece.
3. Avoid running the sander with RPMs or PSI settings too high or too low.
Whether using an electric or pneumatic sander, having the appropriate sander speed (RPM) for your application will be key in achieving a high-quality finish, and avoiding issues like sanding swirls.
On the pneumatic sanders, the main factors contributing to the RPM is having sufficient air pressure and keeping the machine well lubricated. The pneumatics are designed to run optimally with an air pressure of 90 PSI at the sanding machine, and should be oiled daily, if they are used heavily. (Learn more about tips for caring for your pneumatic sanders and getting the optimal results.) Pneumatic sanders also have a speed controller that will allow the user to speed up and slow down the speed of the machine. Unless you are using the sander on a special application which requires a slower speed, the sander should always be set at the highest speed to avoid swirls.
The electric sanders come with a speed setting option that allows the user to change the power/RPMs. Our other article, Electric Sander Speeds 101, goes into much more detail about the specific options available, as well as the advantages/disadvantages of the various speeds, and the applications for each. For the purposes of this article, suffice it to say that the 10,000 RPM range will be ideal for most woodworking applications, unless very fine control is needed for the application.
4. Avoid starting the sander in the air prior to sanding and stopping it while still on the work surface.
Said another way: “Start on, Stop off.” This basic technique is critical in helping to avoid creating swirls at the beginning and ending of the sanding session. The reason for this: making contact with the work piece when the sander is already moving will make it more difficult to get a good contact with the surface; and at the end, the stopping the sander while still on the workpiece means the sander will slow down while still in contact, so it will still be sanding your surface during that lag time. This can lead to an uneven sanding job and swirls.
It’s a simple solution. Always remember: “Start on, Stop off.”
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5. Avoid using the sander on an angle.
One of the most common mistakes people make when using a hand sander is using it as if it were an angle grinder – i.e. using the sander on an angle to the work piece, rather than flat on the surface, in order to sand out a problem area in a surface. A disc or sheet sander is NOT an angle grinder and is designed to be used either with a flat sheet/disc directly on the backup pad (for flat surfaces), with a foam interface pad or hook and loop pad saver and conventional abrasives (application varies), or with foam abrasive (like Ekasilk Plus), for finishing on flat, curved or complex profiles.
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When using a sander on an angle, you are not resolving the issue, rather you’re creating an area that is sanded more than another area, leading to an uneven surface, and therefore an uneven finish. Additionally, this will lead to destroyed discs/sheets and will cause damage to your backup pad, requiring it to be replaced sooner.
If your surface has irregularities, the best options, depending on the severity of the issues and the type of finish you’ll be using, would be to either switch to a coarser grit and sand the whole surface through the whole grit sequence, or use a filler product to fill in the defects and then sand evenly across the whole surface.
Getting a great finish doesn’t have to be difficult. Following some simple techniques, and using quality abrasives, will help to make the process move efficiently and smoothly. It may seem tedious to slow down and sand through the grits, but the results are definitely worth it, and you’ll be able to see, and feel, the difference.
- If you’re new to sanding, check out our other articles to get additional tips, tricks and information to help achieve the best results and avoid/recover from common issues.
- If you want to upgrade your sanding game, but you’re not sure where to start, our articles on Decoding Coated Abrasives give an helpful summary of the technical side of abrasives and a framework for making product selections based on your needs – read Part 1 and Part 2.
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