Control Engineering

Peter Welander

Iron, grease, leather and gasoline: Back to basics
September 18, 2007

After spending the week at the Emerson Global Users Exchange, I was ready to get back to something a bit more basic. PlantWeb, wireless, DeltaV, instrumentation, and the like are very important, but sometimes I want something I can reason with. While I was in Texas, my wife told me that my friend Joe had called, and he wanted to know if I might have some time on Saturday to come over and help him fire up his sawmill.

Joe is not your average neighbor. He is retired after spending his entire career at Argonne National Labs, where he helped design and build the things that the scientists came up with. I got to know Joe after our church bought property and built on the lot across the street from his house. A group of us from the church were trying to plant some trees, and he drove across the street with a tractor and backhoe to give us a welcome hand. After talking to him a bit, I knew I had found a very interesting guy.

Joe’s house is located on a couple acres where he has a house, garages, a greenhouse, chicken coop, barns, machine shop, woodworking shop, blacksmith shop, and a sawmill. I could describe the whole complex over many pages, but I’ll stick with the sawmill for the sake of space. Unfortunately, while I’ve known Joe for seven or eight years, I’ve never been able to see it operate. This was my big chance.

The sawmill includes a pair of rails, probably 25 feet long, a carriage to hold the log, and a 4 foot diameter circular saw blade. Joe’s had it now for about 30 years, and it was pretty old when he bought it. It had been dismantled, so he bought a big pile of parts and had to figure out how to reassemble it. It is driven by a six-cylinder flathead engine that is at least 65 years old and apparently powered a forklift in its earlier life. There’s no electric starter, so the normal way to start the engine is with a crank. Since it is a circular saw, the effective cutting width is about 21 inches, but that is still a pretty big tree trunk.

The drive mechanism to move the carriage back and forth is powered by a series of flat belts. The operator has a lever that he pulls to advance the log, or pushes to bring the carriage back. The mechanism operates by tensioning the right combination of belts and varies speed simply by letting the belts slip. There’s nothing hydraulic here. No variable speed motors. It’s motion control at its most basic.

Joe has no desire to start the engine with a crank, so he put a sheave on the outboard end of the blade shaft and mounted an electric motor next to it on a pivot. When he wants to start the engine from a dead stop, he disengages the clutch on the engine, puts on the belts, starts the electric motor, and rocks it to begin turning the main shaft. When he brings the blade up to speed, he pops the clutch and the momentum of the blade kicks it over. Once it’s running, he takes the belts off and turns off the starting motor. It’s not very sophisticated, but it works.

The carriage holds the log with three hold-downs using claws mounted on a mechanism like a jack. Advancing the log laterally into the blade uses a mechanical system with a movable stop to ensure consistent board thickness. I wish I could describe it in greater detail. Joe stood down at the feed end and stationed me at the delivery. He put on a walnut log, probably 16 inches in diameter, and locked it down. With the engine roaring away, he sent it down the track into the blade.

Standing at the delivery end of a 4 foot circular saw blade gets your attention, especially when there is no guarding around it. The upper half of that blade is whirring away, with nothing between you and it. It has no trouble taking a pass through the log. My job was to pull the cut stock away and sort it between scrap and usable boards. I also had to run and empty the wheelbarrow when it filled up with sawdust. There is a crude but effective conveyor to bring it out of a hole dug below the blade. It creates a lot of sawdust.

I decided early on that I was going to keep my eye on the blade. When something can take off an arm in an instant, you don’t want to get distracted and stop paying attention. Soon John joined us to help out as well. He works for the county forest preserve. It was his first time running the mill too. John and I worked the delivery end while Joe manned the control levers. Sometimes we’d help wrestle a log onto the carriage using a cant hook to roll it into place.

After a few hours, we’d cut up maybe a dozen logs, including walnut, mulberry and hackberry. I had a snoot full of sawdust and a good dose of exhaust fumes, but we still had all our fingers. It was amazing. Joe heated up a pot of wax, and we dipped the ends of the freshly cut boards to keep them from drying out too fast and splitting. Eventually my hearing came back.

We swept up the remaining sawdust and I loaded a whole bunch of walnut boards into my van. I’ll stack them somewhere in my basement, and in a year or so I can run everything through my planer.

While this narrative makes for an interesting bit of Americana, I bring it up to call attention to the fact that there seems to be a whole lot fewer people around like Joe, particularly in our industry. The notion that people involved in engineering should have mechanical hobbies seems to be dying out. In a past life where I was responsible for a group of mechanical engineers, I was puzzled by how few of them seemed to have any natural “mechanical inclination” as individuals. How many people do you know who work on their own cars? Does anybody still build radios? Do you have a drill press in your basement or garage? How about a milling machine? A table saw? A few decades ago, this kind of thing would have been far more common. Now the key skills people want to develop involve the ability to set up an HDTV or download images from a digital camera. Somehow it isn’t the same.

Skills developed from such experiences help us better understand what we’re doing. You can study the characteristics of pipe threads in manuals from now until doomsday, but you will gain far more practical knowledge from cutting a thread yourself. When the opportunity comes to choose how to mount a pressure sensor, that experience could make a huge difference. Perhaps this is another manifestation of the brain drain that is happening with our aging workforce. It will be a difficult one to counteract.

Posted by Peter Welander on September 18, 2007 | Comments (0)