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How to Remove Swirl Marks in Wood Sanding

Eliminate Swirl Marks From Your Finish

In general wood sanding is often viewed as a simplistic process where operators don't need much training, this is not the case. When sanding wood an operator is tasked with removing defects or applying a consistent finish, thus an operator needs to be skilled with the techniques needed to do the job effectively.  This requirement can also be compounded by the fact that a wood sanding operator has to do all this quickly in high production environments. 

What are swirl marks?  

Swirl marks are super fine scratches that are visible to the naked eye.  They are sometimes known as fishhooks, pigtails, or half-moons. 


What causes swirl marks? 

There are four main causes of swirl marks. Below is the cause and a recommendation on how to eliminate them.

  1.  Damaged or worn out back up pads. Damaged back up pads should be pretty obvious, however special attention should be taken with PSA style as debris can be stuck to the disc or the pad in-between the pad and the sand paper.  Keep all types of pads as clean as possible. 
  2. Poorly maintained or worn out orbital sander bearings. Oil daily, repair or replace internal motor parts. This article goes in-depth into air tool maintenance.
  3. Inconsistent air supply or delivery to the sander. Ensuring the air delivery system is adequate for the needs of the tool(s) running on that system. Check out this article for a more in-depth explanation about air delivery systems and how to set them up. Use high flow style air hose quick connections whenever possible.
  4. Improper sanding technique. Always start the sander on the workpiece. When sanding is complete lift the sander off the workpiece before stopping the tool. Do not use excessive pressure. No more than about 4 pounds of downward pressure. Let the sander do the work. Always run the sander flat, never on edge or at an angle. This also prematurely wears out the backup pad costing more money in the long run. 


Use an Appropriate Sanding Pattern

There are 2 basic patterns to consider, however it all depends on the desired final finish that is to be achieved.  See the info-graphics below.

            North-South-East-West                       Sanding with the grain


 The North-South-East-West type of sanding pattern is best suited for when overall coverage and speed is required and final finish is less of a priority.  The Sanding with the grain pattern does exactly what it says.  Keep the sander moving with the grain and do not sand cross grain.  This technique is used when the up-most consistent fine finish is desired above all else.

Armed with this information and a little bit of time, proper training of new employees can lead to more productivity and less re-works because of operator induced finishing defects.

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