Chatter marks are the most common sanding defect and problem and can come from different sources. Common causes and solutions are:
• If the marks are uniformly spread across the board, the rollers being out of balance can cause the problem, or the bearings may be worn. The rollers may have become “oval” or the pad, where fitted, may have become stuck.
• Another cause can be vibration caused by poor machine mounting or loose foundation plates. The spacing between the chatter marks will indicate whether it is the contact roller or a defective abrasive belt.
• Splice marks are similar to chatter marks but are caused by a poor belt splice. There is a difference between the frequency of marks caused by a splice and chatter marks from a roller. To see if the marks are from the drum or the splice, sand two workpieces, one at a fast conveyor speed, and the other at a slow conveyor speed. Compare the marks; if the marks are similar it is chatter from the drum. If the spacing of the marks is different, the abrasive belt splice causes them.
• Make sure your contact roller has the proper rubber hardness (durometer) for your application. Experts recommend a durometer of 60 for most sanding applications. Harder contact rollers will take off more material but they are also less forgiving increasing the likelihood of unwanted marks.
• Use a platen for finish sanding. The platen will sand less per pass and also spreads the sanding over a larger surface area because it is actually wider than the contact roller. Running your material through a couple of times during the finishing process with the platen activated should give you a nice smooth finish.
• Slow it down – Running your conveyor belt slower will allow more time for abrasive sanding to remove the chatter marks.
• Other actions to cure chatter include: Use an abrasive belt with a butt splice; replace the contact drum bearings; replace the drive motor bearings; tighten the drive belts; replace or dress the contact drum; balance the contact drum; check the conveyor bed drive coupler/drive belt; and relieve tension from the abrasive belt when it is not in use to avoid flat spots on drums.