Thu 30 Aug 2012
Posted by Marcin
We have built and run the Open Source Ecology Dimensional Sawmill for the first time. The Dimensional Sawmill allows you to turn logs into dimensional lumber. There are several other types of sawmills, such as the standard circular sawmill, chainsaw mill, bandsaw, and tilt-blade sawmill. A Dimensional Sawmill is a particular type of sawmill which has 2 or more blades – set at a right angle to each other – such that a dimensional piece of lumber is cut from a log in a single pass - which makes it the highest production-rate sawmill of the portable types.
We have built a band saw mill back in 2008, as in the first picture above, and found that band saw blade alignment is not easy on our simple model. We then moved on to the design of the Dimensional Sawmill, with initial concept as in the second picture above. Then we studied an industry standard sawmill and Chris Fornof drew up the Sketchup model as in the 3rd picture above. Chris’s grandfather happened to be familiar with sawmill design and operation – so we made the initial Sketchup design in 2 days by visiting with his grandfather. Then, we got Sweiger Shop to build out the design after a visit to one of the industry standard sawmills that we found in Missouri.
See our initial design rationale – and subject matter expert review wiki page. If you are a subject matter expert yourself – please review this work on the review wiki page, or if you know other professional sawyers or machine designers – please point them to the page.
Cost and Performance
We have built the prototype at a cost of $8k in materials, which is a good start – as the industry standard sawmill of this power costs $34k with a trailer. The overall budget killed us – as $9k went for hired prototyping labor at $55/hour. We got the job done, but paid dearly. It took 184 hours to build – but that is because the prototyper was figuring things out along the way. This time includes mistakes and mid-course corrections. The optimized build should take about 20-40 hours.
The open source ecology dimensional sawmill specifications are:
The initial run was satisfactory though short. Seeing the 2 blades spin and saw dust fly for the first time was rewarding. Since it was our first run, we were cautious. Then one of our Power Power Cubes, Prototype IV, wouldn’t start, so the testing was cut short. We will report soon on persistent Power Cube issues – and the solution with Power Cube VI. We will return to further sawmill testing once the second power unit is back up.
We cut our initial piece of dimensional lumber by starting with the edger blade and main blade to flatten the top. The motion was smooth, but closer examination exposes unacceptable vibration of the main platform. We discovered several lessons and bugs.
- There is unacceptable vibration that makes the kerf wider than it should be. We had up to 5/8″ kerf instead of 3/8″.
- The main motor platform is a flat piece of steel with angle on the sides. It needs to be more stable by building it with tubing instead.
- The main space frame gantry reinforcements vibrate visibly. These need to be reinforced.
- Flow control valve is not effective in speed control. We left it fully open at all times, as we need maximum power
- We did not use the gantry drive, and we are considering mounting the drive on the end of the sawmill, not on the drive platform. Since it is gear-rack drive – and is not trivial to mate properly – we decided to drive it from the end itself using a simpler mechanism such as a reel. This also avoids more hoses going to the platform.
- Wu pushed the gantry manually first to get a feel for the motion. It takes significant effort to move the gantry.
- We drove the edger blade into the wood in the wrong direction. The teeth should be pulling the log through, not going against it. See video below.
- Hose routing is an issue. The hydraulic hoses get in the way. We are considering using a single hose set with the blade motors in series by using larger drive motors to handle the same hydraulic flow. We are using 8 hoses – 3 for each motor including case drain, and 2 for the gantry drive motor. We can get this down to 2 hoses and a couple return stubs for the case drain going to the return line.
- Other small details of machine geometry became obvious after first use, and these will be corrected in the next prototype.
Future work includes completing the test run, and addressing all the issues identified above – and moving on to the next iteration in Prototype II. We expect the second prototype to be deployed in February, 2013, according to this deployment plan that is found in the Strategic Plan, forthcoming.
Beta release is expected in August, 2013. Join us in the development process if you would like to see this sawmill become available to the world at a fraction of the cost of industry standards. If you are a fabricator, this is a great product for your local economy. See the product ecology of the sawmill with respect to the rest of the Global Village Construction Set.
We do not recommend that you replicate this work if you are a novice on grounds of safety. You shoul check in with the development team if you are interested in development collaboration. Our machine is not fully tested, and it is not safe. Replication is recommended to experienced developers who are savvy with heavy equipment.
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