Determining the repair and maintenance cost of wood chippers

Chipping weighs heavily on the total delivered cost of wood fuel, which calls for accurate chipping cost estimates. Chipper repair and maintenance cost is perhaps the most obscure among the figures required for a reliable estimate of chipping cost. To clarify this issue, the authors examined the long-term repair and maintenance records for 51 wood chippers operated by 48 chipping service contractors. Repair and maintenance represented between 1.5% and 29% of total chipping cost, inclusive of fuel and labour (mean = 14%). The ratio between total accumulated repair (TAR) cost and machine price averaged 32% and varied with total use. The relationship between total use and TAR to price ratio was explored through regression analysis, which produced a very strong model (R-2 = 0.8). This model predicts a TAR to price ratio of 0.64 at 10000 h, with no significant differences between tractor-driven and independent-engine machines. While the coefficients are different, the structure of this model offers a good match with the repair and maintenance cost models developed for farm tractors and other agricultural machinery. A second model was developed for estimating repair and maintenance cost as a function of fuel consumption. The study also provides reference figures for the contribution of labour cost to total maintenance cost. Farm tractors incur more repairs than preventive maintenance, contrary to the other dedicated components of the chipping operation, where preventive maintenance represents most of maintenance cost. Forestry users should make allowance for the lower structural strength of tractors and select large models.