Dynabrade Blog

How To Avoid Swirl Marks While Sanding Wood

Sanding on any surface takes practice and patience – it becomes an art form. What happens if you don't have years of experience behind you though and you need that "perfect finish" right now? Dynabrade has proven methods to help get you there.

The top question we are asked is… "Why am I still getting swirl marks on my work piece?"
Well, it's not a simple answer, but going through the below steps should get you to the swirl-free finish you are hoping to accomplish.

Let's start with your sander.

• Random orbital sanders are designed as finishing sanders.
  

  To achieve the best results, use the sander as a "finishing sander". Do not exert heavy downward force on the sander. Apply enough downward force to keep the back-up pad and abrasive flat on the surface while still allowing the back-up pad to orbit freely over the surface.
  Remember – let the sander do the work.

• Always match the sander to your work.
  

  For an aggressive and faster cut rate use a sander with a 3/8" diameter orbit. For moderate cut rate use a 3/16" diameter orbit, and for the lightest cut rate, and the finest in finish sanding use a 3/32" diameter orbit. Excellent results can be accomplished by selecting the correct sanding action, the correct grit abrasive, and the correct sequence of abrasive on the sander.

• Check the orbit diameter that is being used for the application.
  

  A 3/32" orbit would be preferable when using on softer woods that have a more porous texture. The smaller orbit helps to close the pores and allow the wood to take stain and paint better. Otherwise, a 3/16" orbit is the most commonly used on surfaces.

• Is your sander getting 90 PSIG (6.2 Bars)?

  Check the air pressure at the tool while it is running. Obstructions, length of the hose, and other obstacles could be preventing the proper pressure from reaching your tool.

• Confirm that the tool is running at the rated "Free Speed" RPM.

  On an average a 10,000 rpm non-vacuum sander will run at 9,500 rpm; a 12,000 rpm non-vacuum sander will run at 11,500 rpm. A vacuum sander normally runs slightly slower.
  Note: Removing the sanding residue from the work surface with a central or self-generated vacuum sander will improve the finish. It will also help to extend the life of the abrasive. Consider using a vacuum style sander.

Sanding Pad

• Inspect the balancer bearing (pad bearing).
  

  Remove the back-up pad and rotate the balancer bearing shaft while holding the counterbalance stationary. The balancer shaft should turn freely.

• Inspect the face of the sanding pad.
  

  The pad must be flat and smooth, without any defects. Check if they are using a Dynabrade Back-Up Pad that is "weight- mated" to the sander. Using another pad can make the sander vibrate excessively and lead to an unacceptable finish.

Abrasive

• Use a good quality abrasive.
  

  An Abrasive product that has an additive to help prevent loading of the sanding disc will provide a superior finish than abrasive that has no additive. When sanding particularly sensitive surfaces such as Corian® and other acrylic solid surfaces it is best to use a film backed abrasive sanding disc. Film backing forces the abrasive to lie flat on the surface. The grain is then presented to the sanding surface in a very uniform manner.

Sanding Technique

• 1. Always START the sander ON the surface and STOP the sander OFF the surface.
  2. While you are sanding, keep the sander and pad FLAT on the surface. Do not exert too much downward force, just apply enough force to keep the back-up pad and abrasive flat on the surface to allow the back-up pad to freely orbit over the surface.
  3. Follow a pattern while sanding. Many professionals suggest the "North, South, East, West" pattern where you overlap each pass ¼ the diameter of the back-up pad and abrasive. This will ensure that the previous scratches are removed and that a uniform finish is achieved.
  4. Frequently inspect the abrasive for any tears, folds, or build-up. Before proceeding onto the next sanding step, always inspect the abrasive.
  5. If you do notice any abrasive defects, reattach a new abrasive with the same grit and sand the work surface again before proceeding to the next step.
  6. Always clear away sanding dust and abrasive debris before progressing to the next sanding step with a finer "grit" abrasive.

Remember, each application is different. There is no "one size fits all" solution that will work. You may have a few different operators or just one, dust collection/source capture may be your weak point, maintenance of lines, or just adding a 3/32" orbit to your lineup could be the answer. Whatever the solution, we know the struggle. If you need someone to help you, let one of our representatives come out and test your airlines or even just look over your process. We rather help you perfect the finish than be miserable.

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