Why Does Random Orbital Sander Leave Swirl Marks?

Sander leave swirl marks on wood

The random orbital sander is versatile in the workshop. However, after staining a freshly sanded project, you may notice some ugly swirl marks. In this article, I will explain why does random orbital sander leave swirl marks and how you can prevent them. 

A random orbital sander can leave swirl marks due to poor quality sandpaper, improper technique, or an inability to clear the dust from the surface. 

If you’ve had trouble with those pesky swirl marks, this article is here to help. I’ll begin by explaining how people go wrong with the sander. Then we will explain how you can make things right. 

Three Reasons You Get Swirl Marks Using Random Orbital Sander 

There are three main reasons you can get swirl marks when using a random orbital sander. Here we will go over these three sections in detail. 

Hopefully, after reading this article, you will be able to create the cleanest finish you’ve ever had. 

Here are three reasons you get swirl marks with a random orbital sander: 

  1. You’re using improper technique 
  2. Your sandpaper is low quality 
  3. Dust and debris are getting clogged in your random orbital sander 

Each of these categories has several subcategories. Sanding is all about details, so this article will focus on being precise. We will cover everything you need to know in the sections below. 

Proper Technique When Using Random Orbital Sander 

The whole purpose of the random orbital sander is to sand things in a random circular pattern (hence the name) so that swirl marks are eliminated. However, for best results, this tool needs to be in the hands of a knowledgeable operator. 

If you notice swirling lines in your wood after sanding, you may be doing something wrong. It’s always important to assess your technique before you spend money on a new tool. It can be hard to be self-critical, but it’s vital for improvement. 

Here are some things to keep in mind when using a random orbital sander: 

  1. Don’t push too hard 
  2. Be careful how you start 
  3. Move slowly 
  4. Avoid tipping or tilting the sander 

Alright, there are four tips. Let’s go over each one in a bit more detail. 

Don’t Push Random Orbital Sander Too Hard 

You want to have a nice, even pressure on the sander. Don’t allow it to shake around like a crazy chicken. However, you don’t need to hold it too firm either. 

If you push too hard while using the random orbital sander, you end up inhibiting the machine’s designed sanding process and put increased wear on the machine. 

Keep a steady hand on the sander, but not too much. Practice on a few scrap pieces until you’ve got a good feel for it. 

Be careful How You Start with Random Orbital Sander 

The beginning is critical. If you mess this up, it can be a painstaking process to clean things up. 

Many woodworkers suggest placing the random orbital sander on the surface before turning it on. This technique lowers the risk of creating a gouge on the surface. It also allows you to start slow. 

Again, take some time to practice at the beginning. Practice does make perfect. 

Move Slowly with the Random Orbital Sander 

Sanding your project isn’t a race. Unfortunately, the best things in life take some time to get it right. If you push the random orbital sander too fast, you risk leaving behind those nasty swirl marks. 

Instead, try to move your sander one inch every second. This isn’t very fast! However, this does allow the sander to get things polished nicely. 

Also, refrain from stopping and then starting again. Playing red-light-green-light with your sander can cause the surface to become uneven. 

You probably won’t even notice you’ve over-sanded an area until you apply the stain – this isn’t ideal! Just when you thought your project was finished, you have to sand all the blotchy stain off and try again. 

To avoid this, think of sanding the surface like mowing your lawn. Move over the surface in even, regular passes. Some people find it helpful to take a pencil and draw light marks on the surface of the wood – this helps you remember where you’ve sanded. 

Of course, after the rough sanding is finished, you can go over the project by hand with a piece of 220 grit sandpaper. This may eliminate some of those swirl marks. 

Avoid Tipping the Random Orbital Sander 

You want the sanding pad to be planted flat on the surface of your project. If there is pressure to one edge of the sanding surface, you’ll get the swirl marks. You’ll also get an uneven surface. 

How do you prevent this? 

Well, the best way is to grip low on the sander. Instead of pushing down from the top of the sander, wear gloves and grip lower toward the sanding pad. If this were baseball, we might tell you to “choke up” on the bat. 

This technique prevents you from accidentally applying lateral pressure. 

Alright, we’ve discussed your technique. If you’re still getting swirl marks, then you may have a problem with the sander. We’ll tackle this in the next section. 

Low-Quality Sandpaper Causing Swirl Marks 

There are times when you could be doing everything right but still don’t get a clean surface. If that’s you, you’re in the right place because we have a few tips. 

Here are several things that could be wrong: 

  1. Cheap sandpaper 
  2. Wrong sandpaper 
  3. Malfunctioning tool 

Let’s cover these below. 

Cheap Sandpaper Causing Swirl Marks 

Have you ever used a nice kitchen knife? It just cut and cut and was never dull. I’m sure we have all used a dull cheap kitchen knife – it’s miserable, not to mention dangerous. 

The same is true with sandpaper. There’s quality sandpaper, and there’s low-quality sandpaper.

If you get high-grade sandpaper, you are more likely to get a high-grade finish. The abrasive material used in quality sandpaper is more efficient and resistant to clogging. Also, the grit from the sandpaper is less likely to fall off, causing marks and divots. 

Cheap sandpaper is just the opposite. It clogs, wears out, and little pieces will become loose, potentially damaging your project. 

You might think that sandpaper is just sandpaper, but quality does make a difference. Try out some nice sandpaper for your random orbital sander – you may be surprised at the results. 

Wrong Sandpaper Causing Swirl Marks 

Let’s stick with the kitchen knife analogy for a moment. If you buy the most expensive butter knife in the world, it’s still a butter knife – it’s not going to slice tomatoes effectively. 

The same is true with sandpaper. While it’s important to get quality sandpaper, you also want the right sandpaper. 

Some sandpapers are made for wood, some for metal, others for drywall. When shopping for sandpaper, take the time to check what kind you’re getting. 

Also, be sure you’re getting the proper grit. Remember, the higher the number, the finer (or smoother) the grit, 60 grit is quite rough, it’s good for first-pass shaping. On the other hand, 220 grit sandpaper is rather smooth and more likely to give you a clean finish. 

If you’re trying to get a really smooth surface with 60 sandpaper, then you will be disappointed. To avoid swirl marks with your random orbital sander, start with a low grit and work your way up.  

Malfunctioning Random Orbital Sander 

You can buy the most expensive knife in the world, but if you don’t keep it sharp, it’s not going to perform. 

Be sure you follow proper maintenance procedures for your random orbital sander. Make sure nothing is clogging the action of the sander. 

If you’re not sure whether your random orbital sander is working correctly, it’s worth comparing it to someone else’s sander. If you purchased your sander at a yard sale or thrift shop, beware of untold malfunctions. 

While it’s not common for a random orbital sander to fail, keep the possibility in mind, if you’re getting a poorly finished product. 

Failing Random Orbital Sander Vacuum  

Finally, let’s discuss vacuums. Many random orbital sanders will come with a built-in vacuum. The vacuum does more than keep your workshop tidy. 

The act of removing sawdust from your project allows the sander to work at maximum capacity. When you have too much sawdust, it can bunch up under the sander, causing swirl marks. 

Check your vacuum for proper function. Is the collection bag full? Are there any leaks in the tubing? If so, these will need to be repaired. Not only is sawdust bad for your project, but it’s also bad for you. 

A common mistake is forgetting to align the holes on your pad of sandpaper with holes on the machine. Typically, random orbital sanders will have a loop and hook attachment for sandpaper. Just watch to make sure the holes align when applying new sandpaper. 

Also, check to be sure nothing has lodged in these vacuum holes, preventing proper sawdust disposal. 

Last but not least, make sure your surface is clean before sanding. It may seem like sanding is cleaning; however, when sanding, especially at finer grits, big specs of debris can become stuck in the sanding pad, causing dents, dings, and the dreaded swirl marks.