Listed below are some of the most common visible sanding flaws from widebelt sanders – chatter marks, wavy surfaces, ridges and grooves – and the possible sources of the problem.
Chatter refers to the consistent, even lines that may appear across the work piece when something is wrong. While it would be easy to assume the problem is with the abrasive, in reality, the problem is often in the machine. When troubleshooting chatter marks, check the following areas for issues:
Contact roller: You may be using the wrong type of roller for your application – metal or hard durometer rollers are for stock removal purposes only. Your roller may be worn out, out of round or out of balance.
Tension pressure: Check to see that your tension pressure is set correctly, based on the following standards: paper belt – 45-55 psi, cloth belt – 55-65 psi and polyester belt – 65-85 psi.
Belt joint: You may be using the incorrect belt joint style for your application. Check to make sure that your belt has the proper joint and ensure that the tape isn’t too thick for your needs.
Bearings: The bearings on your contact or idler roller may be worn out. Note that this typically reveals itself on one side only.
Conveyor belt: When your conveyor is worn or slick that may cause this issue. If this is the case, dress the conveyor or apply a cleaner to remove excess dust and debris.
Hold-down rollers: Make sure the hold-down rollers are adjusted correctly for your application and workpiece thickness.
Grit sequence: If using a multiple head machine, proper grit sequence and stock removal rate should be checked. Make sure not to skip more than one grit in the sequence.
Formulas: Use the following formulas to determine if the chatter is from the joint or roller. Results should be compared to the actual distance between the chatter marks:
- Joint: [(belt length mm) x (feed speed, m/min)] / [(belt speed m/s) x 60 x (number of joints)] = distance between fault marks in mm
- Roller: [(circumference of roller, mm) x (feed speed, m/min)] / [(belt speed, m/s) x 60] = distance between fault marks in mm
If your workpiece comes out of the sander with a wavy surface with consistent peaks and valleys, this could be coming from the machine or the sandpaper. Check the following:
Contact roller: Wavy surfaces can result from using too soft of a roller for your application, a damaged roller, incorrect grit choice for the application, or too high of a feed speed.
Pad (platen): Platens are typically used for finish sanding, so if you are attempting to remove too much stock in relation to grit choice on this section of the machine you may get a wavy surface. Additionally, if you have too high sanding pressure or too flexible of a pad, a wavy surface may come about.
Grit combination: If you are trying to remove too much material or you skip too many grits, you may have an unsuitable grit combination in the following ranges #80-150 and #100-180. It’s recommended that you never skip more than 1 grit in a sequence.
Ridges (raised lines)
Raised lines on the workpiece can show up in a few different patterns. Identifying the pattern can help determine and isolate the source of the problem.
Short, close, parallel to the length of the workpiece, in a step formation: Belt speed is too low; too much stock removal; too high sanding pressure; too hard and too wide pad; or slightly clogged belts.
Medium length and spread apart, occurring in random locations: Too much stock removal and too high sanding pressure; too high belt speed; too low belt speed; poor dust extraction; or poor cleaning of the belt.
Wavy line along the length of the workpiece: Part of the belt is clogged (hot melt glue, resin, lacquer); or abrasive grains may be damaged by impurities in the workpiece (sand, pins, other metal particles).
1 line along the length of the workpiece: Damaged graphite cloth; damaged contact roller; or compressed felt.
Scratches (grooved lines)
Scratches, or grooves, the opposite of raised lines, can also show up in a few different patterns on the workpiece. Similarly, identifying the pattern of the scratches can help determine and isolate the source of the problem. Typically, if you’re seeing scratches like these, the problem will be related to maintenance issues on the machine, such as the graphite cloth, pressure beams or rollers, or maintenance issues on the belt, such as problems with the joints or the abrasive coating.
1 long line, spanning the length of the workpiece: Contaminated graphite cloth; or contaminated pressure beams.
Short parallel lines in a wave formation: Contaminated belt joints; or cracks in the abrasive coating.
Dashed line along the length of the workpiece: Contaminated pressure rollers.
Source: Uneeda Enterprizes. For information, call 877-863-3321 or visit sandpaper.com.
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