'Chatter Marks' is a well-known term in the floor sanding industry all over the world. It describes a closely spaced repeating drum or 'ripple' mark which is visible in the floor following the sanding procedure. Impossible to feel with the hand, chatter marks often show up more obviously when the finish is applied to the floor and can ruin what could otherwise have been a great job.
Many floor sanding contractors literally spend hours cutting these chatter marks out of the floor with a rotary sander and while they might succeed at removing the 'chatter', they create another problem; circular marks in the floor which can look even more unsightly than the original imperfection that they were trying to correct. In any case, using a rotary sander to remove chatter marks is one of the biggest time-wasters in the floor sanding industry today. Understanding some of the causes of chatter marks and knowing how to rectify them will enable you to improve the quality of your work and save valuable time.
Worn or out-of-balance sander parts often create vibration that produces chatter. These vibrations are often difficult to detect while the machine is operating. Sophisticated vibration monitoring equipment is the most effective way of detecting the source of any problems rather than a time consuming trial and error process. Regular machine servicing including cleaning and checking for wear of drums, wheels, bearings, fans, pulleys, V-belts and belt- sander roller systems is highly recommended. Whether you own a conventional slotted drum or a continuous belt-sander, your equipment must be well maintained in order to avoid chatter marks that are commonly caused by one or more of the following;
(a) The sanding drum. This is often the first place to start. Before balancing is carried out, the technician can ascertain any drum run-out to indicate that the drum is 'out-of-round'. This should be rectified before any balancing work is done.
(b) Bearings. Check all the bearings with the machine turned off. It is often not the bearing itself, but worn bearing housings that can cause vibration problems.
(c) Fan blades. Often operating at speeds of up to 8,000 rpm, even the smallest chip on a fan blade will produce vibration.
(d) V-belts. Worn or cracked V-belts should be changed. Routine replacement once a year is a good rule of thumb.
(e) Motor. Vibration could emanate from an out-of-balance rotor shaft. Likewise, drum mounting shafts that have been knocked or are worn may need re-balancing or replacing.
(f) Pulleys. An unbalanced pulley will also cause vibration. Worn or chipped pulleys should be replaced.
(g) Drum condition. Check that the drum covering (either rubber or felt) is in good condition with no signs of delamination. Before having the drum dynamically balanced, it should be thoroughly cleaned. Depending on the drum design, it may be necessary to use compressed air to blow out months and perhaps years of dust build-up. This super-fine dust can collect inside the drum and cause imbalance; most commonly with conventional drums.
(h) Rollers. If you have a belt sander, the roller assembly should be removed, cleaned and checked for smooth operation. Look for wear and check that the bearings are running smoothly. Servicing the upper roller should be carried out at regular intervals.
(i) Wheels. Check all wheels for dirt or hard filler that may be adhered. Use a scraper to gently remove putty or a solvent soaked cloth to dissolve dirt. Wheels should be checked for flat spots and being out-of-round. You might go so far as to leave the machine with wheels off the ground when not in use.
(j) Conventional drums. For many reasons, these seem to be more prone to leaving chatter marks than continuous belt drums. The most obvious difference is the large gap in the drum. If you use packers (strips of sandpaper) to help get the paper tight, try placing them behind the end flaps of the sandpaper, instead of between the flaps. This will reduce the size of the gap slightly. Having the paper too tight or too loose may also affect the amount of chatter. Experiment with different tensions to get the best results.
(k) Uneven paper tension. This will be obvious if the paper is tighter at one end of the drum compared to the other. Uneven tension will contribute to vibration and can often be heard as a flapping sound when the drum is lowered to the floor during sanding.
(l) V-belt tension. Assuming they are in good condition, try tightening or loosening the V-belts. This can reduce overall machine vibration and chatter marks as a result. Pay particular attention to the smaller V-belt that drives the fan. This is often overlooked and can contribute noticeably to machine vibration.
(m) Excessive drum pressure. Using too much drum pressure, especially when fine sanding, can cause the left or right wheel to leave the floor which results in uneven drum pressure. Using the lowest setting when fine sanding will give you a much better result. It is often not a good idea to put extra pressure on the drum by pushing down on the drum pressure handle or pulling up on the machine, especially when walking backwards.
(n) Worn abrasives. If the sandpaper is worn, the floor can show chatter marks. Some contractors deliberately dull sandpaper to 'burnish' the floor. This practice is not a good idea if you want to reduce chatter marks.
Ridding floors of chatter marks is often a matter of trial and error. The difficulty is that they are often caused by a combination of factors. Sometimes chatter marks are mistaken for 'waves'. In other words, ripples which are more widely spaced. Waves are often the result of the sanding technique employed by the operator.
(o) Sanding speed. The speed at which you allow the machine to move is often critical to the final finish. Moving the machine too quickly or too slowly can often create a wave effect in the floor. Depending on the machine you are using, experiment by walking faster or slower if 'waves' are a problem.
Thankfully, although customers will complain about scratches and dust in coatings, edger marks and other imperfections in the floor, it is rare to hear a serious complaint regarding chatter marks. However, if your drum or belt sander is working as it should and the correct sanding technique is used, you should be able to achieve a finished floor that is ripple free.
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