Sawmill Analysis: Difference between revisions
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Standard wood frame home construction consumes about 6 board-feet(bf) (1x12x12 inch unit volume of wood) per square foot of floor area. Allow an additional 6 board feet for other wood used such as workshops, fences, and furniture. USA average dwelling size is 750 square feet per person. Therefore 750x12 = 9000 board feet of finished lumber/person is needed for construction. Allow 20% defects and drying loss and 10% waste during construction, thus 70% net used lumber. So initial cutting need is 9000/70% = 12,850 bf/person. | Standard wood frame home construction consumes about 6 board-feet(bf) (1x12x12 inch unit volume of wood) per square foot of floor area. Allow an additional 6 board feet for other wood used such as workshops, fences, and furniture. USA average dwelling size is 750 square feet per person. Therefore 750x12 = 9000 board feet of finished lumber/person is needed for construction. Allow 20% defects and drying loss and 10% waste during construction, thus 70% net used lumber. So initial cutting need is 9000/70% = 12,850 bf/person. | ||
1250 people x 3.33% annual construction = 41.67 cutting need per year. 41.67 x 12,850 bf = 535,400 bf/year/machine. Assume 240 working days per year. Thus daily production would need to be 535,400/240 = 2230 bf/day/machine. | 1250 people x 3.33% annual construction = 41.67 cutting need per year. 41.67 x 12,850 bf = 535,400 bf/year/machine. Assume 240 working days per year. Thus daily production would need to be 535,400/240 = 2230 bf/day/machine. Experience shows about half the time is consumed in log setup, board stacking, sawdust removal, and blade maintenance. Thus you have a daily productive cutting time of 4 hours per day. The [http://www.woodmizer.com/us/KnowledgeCenter/SawmillsSawing/SawmillComparison.aspx Wood Mizer] commercial bandsaw mill indicates their LT40SH model can reach the required 2230/4 = 560 bf/hour production rate. | ||
An average crew of 2 is required to operate this size sawmill. During construction, when 2 units are required, that means 4 working people are needed out of 568 available working people in the 1250 total person village, or 0.7% of total village labor. Some additional labor will be needed to cut trees into logs, dry the wet lumber in a kiln, and dispose of offcuts (the parts of a log not turned into lumber) and sawdust. | |||
This result is highly dependent on the assumptions made. Buildings can be primarily made from other materials than wood. Techniques like [http://www.theecologist.org/green_green_living/home/747067/roundwood_timber_framing_the_greener_way_to_build.html Roundwood Construction] use whole log segments without cutting. So the requirement for the sawmill will depend on how the rest of the Village is designed. | |||
Revision as of 13:56, 12 May 2011
Preliminary analysis based on requirements at Sawmill - Design Rationale. As more details of the rest of the village system is developed, this will need to be updated in an iterative fashion.
Production Requirement
Modern sawmills are highly productive devices, so assume 1250 person Village size, the largest size for analysis. Allow 15 year construction period, followed by maintenance and remodeling. Thus 6.67% of construction lumber is needed per year. Allow 1% replacement lumber per year for maintenance and 2% for remodeling, thus 3% per year after construction. Given those numbers, it seems reasonable to build two units with 3.33% annual capacity each. The second unit is either recycled after 15 years or sold off.
Standard wood frame home construction consumes about 6 board-feet(bf) (1x12x12 inch unit volume of wood) per square foot of floor area. Allow an additional 6 board feet for other wood used such as workshops, fences, and furniture. USA average dwelling size is 750 square feet per person. Therefore 750x12 = 9000 board feet of finished lumber/person is needed for construction. Allow 20% defects and drying loss and 10% waste during construction, thus 70% net used lumber. So initial cutting need is 9000/70% = 12,850 bf/person.
1250 people x 3.33% annual construction = 41.67 cutting need per year. 41.67 x 12,850 bf = 535,400 bf/year/machine. Assume 240 working days per year. Thus daily production would need to be 535,400/240 = 2230 bf/day/machine. Experience shows about half the time is consumed in log setup, board stacking, sawdust removal, and blade maintenance. Thus you have a daily productive cutting time of 4 hours per day. The Wood Mizer commercial bandsaw mill indicates their LT40SH model can reach the required 2230/4 = 560 bf/hour production rate.
An average crew of 2 is required to operate this size sawmill. During construction, when 2 units are required, that means 4 working people are needed out of 568 available working people in the 1250 total person village, or 0.7% of total village labor. Some additional labor will be needed to cut trees into logs, dry the wet lumber in a kiln, and dispose of offcuts (the parts of a log not turned into lumber) and sawdust.
This result is highly dependent on the assumptions made. Buildings can be primarily made from other materials than wood. Techniques like Roundwood Construction use whole log segments without cutting. So the requirement for the sawmill will depend on how the rest of the Village is designed.