Effect of planing on warp in Scots Pine (Pinus sylvestris)

Abstract

If a sawn board or plank that is warped after drying is being planed, the feed rollers and the pressure elements will more or less straighten the wood during planing. However, when the pressure is released, some degree of warp will recur since the wood will spring back. With a large amount of straightening, only the cross-sectional dimensions of the wood should be affected by the planing operation, leaving warp unchanged, while a small amount of straightening should have a larger impact on warp. The objective of this study was to evaluate how warp is affected by planing in an industrial planer with standard configuration. A total of 20 pine planks with the dry target dimension 50 mm×150 mm were selected, of which half were severely warped. The worst twist, crook and bow per two metres and maximum cup were measured both before and after planing.

The planer in the experiment had different impacts on the different warp types. For the individual planks, twist was reduced by 25% and crook was reduced by about 20% on average. Although bow decreased for half of the planks, the total average change for individual planks was a slight increase. Cupping practically vanished.

Keywords:

• Bow
• crook
• cup
• Pinus sylvestris
• planing
• Scots Pine
• skip
• twist
• warp

Acknowledgements

The author wishes to thank the European Regional Development Fund, Objective 2, Northern part of Sweden via Tillväxtverket (the Swedish Agency for Economic and Regional Growth) and Vinnova (the Swedish Agency for Innovation Systems) for financial support.