Wide belt sanding is anything but simple, so when you’re experiencing problems it can be complicated to isolate and identify the source of the issue. Whether you’re seeing visual defects on the work piece, or problems inside the machine or with your belts, that can definitely be frustrating, especially when your wide belt sander is a key part of the manufacturing process.
Our wide belt technicians see several common issues, from chatter and other surface faults, to burned belts and too much dust, and they help our customers to get their sander back up and running and improving the overall process and results.
Overall, three common themes arise for the sources of the most common issues – 1. machine maintenance issues, 2. incorrect sanding procedures/techniques/settings, 3. problems with the belt.
This in-depth article, and the upcoming Part 2, goes into the different sanding flaws and machine maintenance issues that will most likely be the source of your issues.
From chatter to grooves and ridges, the most common visible sanding flaws from wide belt sanders and their sources
1. Chatter Marks
What is Chatter? 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:
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.
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.
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.
The bearings on your contact or idler roller may be worn out. Not that this typically reveals itself on one side only.
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/debris.
Hold Down Rollers
Check to make sure that the hold down rollers are adjusted correctly based on your application and work piece thickness.
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.
Use the following formulas to determine if the chatter is from the joint or roller. Results should be compared to actual distance between the chatter marks:
2. Wavy Surface
If you’re work piece comes out of the sander with a wavy surface, as seen in the image, with consistent peaks and valleys, this could be coming from the machine or the sandpaper. Check the following areas to ensure proper maintenance and sanding technique.
Wavy surfaces can result from using too soft of a roller for your application, a damaged roller, incorrect grit choice for application, or too high of a feed speed.
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.
If your belt is too loaded, or you’ve’ had a long interval between belt changes, this could be the source of the problem.
If you are trying to remove too much material or you skip to many grits, you may have an unsuitable grit combination in the following ranges #80-150 and #100-180. Review the grit choices and test other options. Uneeda recommends never skipping more than 1 grit in a sequence.
3. Ridges (raised lines)
Raised lines on the work piece can show up in a few different patterns. Identifying the pattern can help determine and isolate the source of the problem. Some of the problems are related to the sanding action, technique and machine settings, while others are more maintenance related.
Short, close, parallel to length of work piece, in a step formation
Belt speed too low
Too much stock removal
Too high sanding pressure
Too hard and too wide pad
Slightly clogged belts
Medium length and spread apart, occurring in random locations
Too much stock removal & too high sanding pressure
Too high belt speed
Too low belt speed
Poor dust extraction
Poor cleaning of belt – may be due to too low belt speed
Wavy line along length of workpiece
Part of belt clogged (hot melt glue, resin, lacquer)
Abrasive grains damaged by impurities in workpiece (sand, pins, other metal particles)
1 line along length of workpiece
Damaged graphite cloth
Damaged contact roller
4. Scratches (grooved lines)
Scratches, or grooves, the opposite of raised lines, can also show up in a few different patterns on the work piece. 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 length of work piece
Contaminated graphite cloth
Contaminated pressure beams
Short parallel lines in wave formation
Contaminated belt joints
Cracks in abrasive coating
Whether you’re seeing chatter, waves, ridges or grooves, no doubt it can be arduous to identify and resolve the source of the issue. We hope that this article can be a good reference and starting point to help you get the best finish possible.
Stay tuned for the second part of this article, going over issues like dust and static, broken and burned belts, and tracking issues.
Download the article to keep as a reference guide.