Waves on Sanding Result

One of the sanding marks caused by Wide Belt Sander (WBS) is uneven or wavy sanding result.

Figure 1. Front view of wavy sanding result




There are some reasons that may cause wavy sanding result such as

1. Contact drum is too soft
Rubber hardness at the contact drum may be measured by using a durometer. A WBS used with rubber hardness of contact drum that is not fit with the application may cause wavy surface of the sanded panel. The hardness of the contact drum's rubber is expressed in Shore degree (°Shore), namely between 90° - 20° Shore. The higher the Shore degree is, the harder the contact drum's rubber.

2. Sanding Pad is too soft
Like contact drum, sanding pad that is too soft may cause wavy surface. The hardness of sanding pad at some machines that are using pneumatic system depends on the air pressure supplied to the pad. The higher the air pressure is, the harder the pad will be. The hardness of the sanding pad that does not use pneumatic system may be measured from the density of its felt. Felt hardness ranges between 0.2 to 0.6g/cm3. The higher the density level is, the harder the felt will be.

3.Feeding speed (conveyor speed) is too high
The rotational speed of conveyor is called as feeding speed measured in meter per minute (m/minute) unit. Feeding speed highly influences the sanding machine to make abrasion.
Sometimes, for certain type of wood, too high feeding speed may cause waves to the sanding result. Feeding speed for softer wood ranges between 12 - 17 meter per minute. While for hardwood, it ranges between 6 -12 meter/minute.

Sample of wavy sanding result caused by feeding speed
Figure 2. Wavy sanding result with fairly deep groove. Feeding speed 17meter/minute










Figure 3
The wave on the panel surface will be reduced when the feeding speed is lowered to 10 meter/minute









Figure 4
Wave on the panel surface starts to vanish. The lowes feeding speed is 6 meter/minute











4. Sanding pressure is too high and abrasive grits is too fine
The sanding pressure on panel surface may also influence the sanded panel surface to wave.
Sanding pressure that is too high, in combination with too fine grit may cause waves to the panel
surface. Therefore, it is recommended to reduce the sanding pressure, and replace
the sandpaper with the coarser one to improve the sanding result.

5. Sand harshness
Sand harshness will be reduced after a long term of application. This is due to saw dust clogging
to the sandpaper surface affecting the abrasiveness of the sandpaper. The reduced abrasiveness of sand may cause wavy sanding surface.

Woodmag, No. 18, Sep 2008
Magazine for Ekamant's Premier Customer