Troubleshooting Wavy Lines with a Widebelt Sander

      Oscillation or chatter marks can be reduced with adjustments, but could be caused by a defective belt. September 5, 2011

We have a two head 42 inch wide Butfering sander. We bought it new about eight years ago. We use it regularly but we are not a high production shop. It has lately been producing wavy lines on the product. This seems to happen whether or not we also engage the platen. The machine has good dust extraction and we are using top of the line 3M purple belts. The belts are paperbacked and are uni-directional. They have a serpentine stitch rather than a continuous seam.

We had a machinery repairman here today. He is a former Stiles mechanic and presumably reasonably qualified. His determination was that the steel rollers and rubber rollers were in very good condition. He could not find any problem with them. He could also not identify the cause of the wavy lines. He took a sample board with him to consult with others in his field. To try to get in front of this a little bit I thought I would ask here if anybody else has seen a problem like this, and if anybody has a suggestion where to look?

Forum Responses
(Solid Wood Machining Forum)
From contributor G:
Iím not exactly sure what type of wavy lines youíre getting, but sometimes lines are seen on pieces as chatter marks. Most sander operators have seen this, coming from the belts' splice. Test for this by smearing craylon (like bright blue) onto the belt splice, which will give color to the chatter marks as the belt rotates and the splice strikes the piece (for a few turns). Also if you turn the machine conveyor speed up and if you have marks from the belt splice those marks will get wider apart. Slow it down, they get closer.

From contributor G:
Chatter marks are so easy to identify now I'm thinking youíre probably up on all that. Another thing you can do is turn the belt around and see if the wavy line follows with the belt or remains unchanged (in the exact same position). This can show that the belt is or is not the problem. A defective belt or a damaged belt (staple in wood) can give a slightly raised wavy line, (area with abrasive removed from belt by staple) and will usually follow with the belt when itís reversed.

From contributor U:
If it is wavy running front to back, then it is most likely the belt because the oscillation plus forward motion is what creates it. If it were a roller defect, then it would just be a straight line.

From contributor T:
Sometimes just changing the belt (even if it is new) will get rid of this. Also you can take a piece of chalk or lumber crayon, flatten out a side rubbing on an old sanding belt and then gently rub your sanded piece of wood. You will see what else is going on too.

From contributor K:
We have the same machine and those are oscillation marks. You may need to adjust the air regulator or change the air pressure on the heads, it could be bad belts. We also use 3M 970dz belts and sometimes they are defective.

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