You are planning up some rough lumber for your next fine furniture project. After the first few passes the roughness is mostly gone and the rich grain pattern is becoming visible. But then after a pass through the bench top planner you notice that the surface of the planned wood is pitted with what looks like pot marks or dents. What is going on to cause this?
Chip prints are slight to moderate indentations left in the wood after a pass through a surface planner. During the planning pass wood chips are either caught between the planner knife and the wood or between the out feed roller and the wood.
Hardwoods are more susceptible this type of damage than softwoods. Seems a bit odd doesn’t it? Softwoods are able to ‘bounce’ back more easily than hardwoods by their nature.
Most bench top planners have a pretty good wood chip ejection. Delta and DeWalt have a blower fan to force the chips out of the back of the bench top planner. However, these bench top planners still tend to spit out wood chips to the front of the machine.
Another culprit is dry heated air. If you are fortunate enough to have a heating system in your wood shop, the dry warm air can cause the wood chips to ’stick’ to the freshly planned wood. Wood chips are typically negatively charged when freshly cut from the wood, whereas the freshly machined wood has a slight positive charge. In the winter months when using a heater, the air is dryer and has a lower relative humidity. This results in the wood chips and the freshly machined wood to take longer to dissipate their static charges.
The static charge causes the wood chip to ’stick’ on the freshly machined lumber and then the chip is pressed into the wood by the out feed roller or planner knife. The results are very unpleasant.
In the next post will present several options to reduce this problem.
