The sawmill project has undergone some changes in design since the last concept. I have taken over development, and based on a comment on the previous concept we decided to pursue a different design, a dimensional sawmill. A dimensional sawmill is one with multiple blades that work on a stationary log. Because they have multiple blades, they can cut out a piece of dimensional lumber in only one pass. This makes them very fast in lumber production.
We chose a dimensional sawmill because it has the highest output, and the simplest design for personal fabrication – a circular sawmill with 3 blades. These two requirements are high priorities for Global Village construction. A circular blade can be fabricated easily, such as by cutting from a sheet with a torch table. Swing blade sawmills – where a single circular saw and motor rotate/swing to make different angled cuts – are apparently not stable enough to provide the output that they claim – according to feedback from two foresters. Plus, the swing mechanism is more complex. A chainsaw mill is the simplest, but it just doesn’t provide the required output for effective Global Village construction. Dimensional sawmills have the highest output of portable sawmills, but the industrial ones are also the most expensive.
The industrial designs use gas or diesel engines and also carry the engine with the saws on the platform, whereas ours will have hydraulic motors – powered by the open source tractor, LifeTrac – for 40 hp of available cutting power. The hydraulic drive allows for great simplification in gearing requirements, as well as great simplification of the vertical motion mechanism, as will beome apparent in forthcoming work. The sawmill project will be another experiment in “factor 10” engineering, attempting to reduce the cost of machines by a factor of ten. Our goal is nothing short of high performance – a mill that cuts wood like butter.
So far we’ve decided on a design similar to the MDS, with a space frame (for stability) on two ‘I’ beams for x and y axis movements, a chassis surrounding the space frame with bearings to grip it on all sides, a vertical plate or beams on the chassis with another plate attached with bearings and adjusted vertically with a pulley for the z axis, the MDS like saws are mounted on the vertically moving plate and powered with hydraulic motors and pulleys to get the correct RPM.
A 2D top view layout has been done and some research is on the wiki:
The next step is going to be to make a prototype of the space frame, with a bill of materials, budget, and implementation plan. We need some research on space frames for that.
If anyone has advice, suggestions, ideas, questions, or can help on the design please post in the blog comments, or on the wiki sawmill dicscussion page. Please feel free to rearrange the sawmill page for a better workflow, it’s a work in progress.