Michael Heggen 💯🐸 ❌👑
@michaelheggen.bsky.social
Farmer, forester, sawyer, builder, fencer, horseman, juggler, husband, mentor, tabletop gamer, feminist, Oregonian, LGBTQ+ ally, reader, lifelong learner, neuro-divergent nerd (no particular order).
Resident of Oregon's 6th Congressional district (OR-6).
Resident of Oregon's 6th Congressional district (OR-6).
I am in season 3 of Homeland. Great television!
December 4, 2025 at 7:43 AM
I am in season 3 of Homeland. Great television!
Meta-gaming is a force to be reckoned with.
I have become hypersensitive to the presence of Chekov’s _____ in television and film. I loves me some writing that is not mired in such spoonfeeding.
I have become hypersensitive to the presence of Chekov’s _____ in television and film. I loves me some writing that is not mired in such spoonfeeding.
December 2, 2025 at 5:59 AM
Meta-gaming is a force to be reckoned with.
I have become hypersensitive to the presence of Chekov’s _____ in television and film. I loves me some writing that is not mired in such spoonfeeding.
I have become hypersensitive to the presence of Chekov’s _____ in television and film. I loves me some writing that is not mired in such spoonfeeding.
We went a couple of steps up from Harbor Freight, but yeah.
And funny that you should mention that, because a previous project with my buddy Mark was a pulley/leverage machine for dumping manure into a compost bin that we dubbed the Trebushit. It was effectively the reverse of a trebuchet. :-)
And funny that you should mention that, because a previous project with my buddy Mark was a pulley/leverage machine for dumping manure into a compost bin that we dubbed the Trebushit. It was effectively the reverse of a trebuchet. :-)
December 2, 2025 at 1:26 AM
We went a couple of steps up from Harbor Freight, but yeah.
And funny that you should mention that, because a previous project with my buddy Mark was a pulley/leverage machine for dumping manure into a compost bin that we dubbed the Trebushit. It was effectively the reverse of a trebuchet. :-)
And funny that you should mention that, because a previous project with my buddy Mark was a pulley/leverage machine for dumping manure into a compost bin that we dubbed the Trebushit. It was effectively the reverse of a trebuchet. :-)
🧵 How We Built Our Bridge, part 6
Link to Part 5:
bsky.app/profile/mich...
Here's a perspective view of the main span design, showing ten wooden arches tied together. Details in alt text.
For smaller versions, 2-4 arches are used. We needed more for our design weight.
Link to Part 5:
bsky.app/profile/mich...
Here's a perspective view of the main span design, showing ten wooden arches tied together. Details in alt text.
For smaller versions, 2-4 arches are used. We needed more for our design weight.
December 1, 2025 at 4:59 PM
It turns out that 135-ish feet of 3/8" swaged wire rope does indeed have a non-trivial amount of catenary sag—even with nearly 12,000 lbs. of tension.
But that telling will have to wait until the next chapter, because now I have to go feed the horses.
But that telling will have to wait until the next chapter, because now I have to go feed the horses.
November 30, 2025 at 11:17 PM
It turns out that 135-ish feet of 3/8" swaged wire rope does indeed have a non-trivial amount of catenary sag—even with nearly 12,000 lbs. of tension.
But that telling will have to wait until the next chapter, because now I have to go feed the horses.
But that telling will have to wait until the next chapter, because now I have to go feed the horses.
Because you need to know how tall to make the shearlegs. You just need a vague idea of how much sag you will have so that your skyline will be high enough to move the load.
Unfortunately, we didn't take catenary sag into account because we thought it would be trivial on this short of a span.
Unfortunately, we didn't take catenary sag into account because we thought it would be trivial on this short of a span.
November 30, 2025 at 11:17 PM
Because you need to know how tall to make the shearlegs. You just need a vague idea of how much sag you will have so that your skyline will be high enough to move the load.
Unfortunately, we didn't take catenary sag into account because we thought it would be trivial on this short of a span.
Unfortunately, we didn't take catenary sag into account because we thought it would be trivial on this short of a span.
No matter how much tension you apply, you will not be able to eliminate all of the sag. Eventually the line will break or the anchor will fail.
But, you say, you aren't building a suspension bridge, so why do you care about catenary sag?
But, you say, you aren't building a suspension bridge, so why do you care about catenary sag?
November 30, 2025 at 11:17 PM
No matter how much tension you apply, you will not be able to eliminate all of the sag. Eventually the line will break or the anchor will fail.
But, you say, you aren't building a suspension bridge, so why do you care about catenary sag?
But, you say, you aren't building a suspension bridge, so why do you care about catenary sag?
You can experiment with this using twine, rope, and chain—all of the same length (at least 20 feet to make things easy to see). Attach one end to a fixed object; apply the same horizontal tension to the other end of each; observe how the amount of sag varies.
November 30, 2025 at 11:17 PM
You can experiment with this using twine, rope, and chain—all of the same length (at least 20 feet to make things easy to see). Attach one end to a fixed object; apply the same horizontal tension to the other end of each; observe how the amount of sag varies.
There is Some Math to calculate this catenary sag, but it is mainly a function of the distance between supports, the tension on the cable, and the weight of the cable itself. If you look at photos of the Golden Gate during construction, the sag is there even with no roadbed in place.
November 30, 2025 at 11:17 PM
There is Some Math to calculate this catenary sag, but it is mainly a function of the distance between supports, the tension on the cable, and the weight of the cable itself. If you look at photos of the Golden Gate during construction, the sag is there even with no roadbed in place.
There are towers with massive cables hanging between them, which in turn have smaller cables holding up the roadbed. The main cables typically swoop all the way down to roadbed. The reason for the swoop and the height of the towers is because gravity makes the cables sag.
November 30, 2025 at 11:17 PM
There are towers with massive cables hanging between them, which in turn have smaller cables holding up the roadbed. The main cables typically swoop all the way down to roadbed. The reason for the swoop and the height of the towers is because gravity makes the cables sag.
Come-alongs allow a single person to easily move multi-ton loads. They are also a excellent way to apply tension to rigging.
And that brings us to another bit of jargon: catenary sag. To explain this, imagine a suspension bridge like the iconic Golden Gate Bridge in San Francisco.
And that brings us to another bit of jargon: catenary sag. To explain this, imagine a suspension bridge like the iconic Golden Gate Bridge in San Francisco.
November 30, 2025 at 11:17 PM
Come-alongs allow a single person to easily move multi-ton loads. They are also a excellent way to apply tension to rigging.
And that brings us to another bit of jargon: catenary sag. To explain this, imagine a suspension bridge like the iconic Golden Gate Bridge in San Francisco.
And that brings us to another bit of jargon: catenary sag. To explain this, imagine a suspension bridge like the iconic Golden Gate Bridge in San Francisco.
A come-along (or cable puller) is a hand-operated winch. A lever handle is attached to a drum with a length of cable wrapped around it. One end of the cable goes to the load. The lever arm and the drum creates mechanical advantage. A ratchet mechanism holds the load when no force is being applied.
November 30, 2025 at 11:17 PM
A come-along (or cable puller) is a hand-operated winch. A lever handle is attached to a drum with a length of cable wrapped around it. One end of the cable goes to the load. The lever arm and the drum creates mechanical advantage. A ratchet mechanism holds the load when no force is being applied.
A Dutchman block is a pulley (a block) suspended from the skyline; a line connects the pulley to an anchor on the ground at roughly a right angle to the skyline. By pulling on the Dutchman block, the skyline can be shifted laterally, allowing a limited lateral movement of a load on the skyline.
November 30, 2025 at 11:17 PM
A Dutchman block is a pulley (a block) suspended from the skyline; a line connects the pulley to an anchor on the ground at roughly a right angle to the skyline. By pulling on the Dutchman block, the skyline can be shifted laterally, allowing a limited lateral movement of a load on the skyline.
So, a set of shearlegs supporting a skyline with a trolley would enable us to move the arches into position with the addition of two additional bits: a Dutchman block and some come-alongs.
I'm not making these names up, I swear.
I'm not making these names up, I swear.
November 30, 2025 at 11:17 PM
So, a set of shearlegs supporting a skyline with a trolley would enable us to move the arches into position with the addition of two additional bits: a Dutchman block and some come-alongs.
I'm not making these names up, I swear.
I'm not making these names up, I swear.
A chain hoist uses a loop of chain to drive a gear that drives another gear that is connected to different chain that supports the load. The difference in the sizes of the two gears determines the mechanical advantage. A mechanical brake keeps the load in place when no force is being applied.
November 30, 2025 at 11:17 PM
A chain hoist uses a loop of chain to drive a gear that drives another gear that is connected to different chain that supports the load. The difference in the sizes of the two gears determines the mechanical advantage. A mechanical brake keeps the load in place when no force is being applied.
If you support that load with a pulley, you can move that load back and forth on the line. This usage is called a skyline.
If you suspend a load on a skyline from two pulleys connected together by a frame, that is called a trolley. A trolley allows a load to move more smoothly on a skyline.
If you suspend a load on a skyline from two pulleys connected together by a frame, that is called a trolley. A trolley allows a load to move more smoothly on a skyline.
November 30, 2025 at 11:17 PM
If you support that load with a pulley, you can move that load back and forth on the line. This usage is called a skyline.
If you suspend a load on a skyline from two pulleys connected together by a frame, that is called a trolley. A trolley allows a load to move more smoothly on a skyline.
If you suspend a load on a skyline from two pulleys connected together by a frame, that is called a trolley. A trolley allows a load to move more smoothly on a skyline.
You now have a lifting device that can use pulleys or some other form of MA to lift a load and move that load forward or backward by changing the angle of the shearlegs (a process called luffing).
If you have two shearlegs, you can rig a line between them to support a load anywhere along that line.
If you have two shearlegs, you can rig a line between them to support a load anywhere along that line.
November 30, 2025 at 11:17 PM
You now have a lifting device that can use pulleys or some other form of MA to lift a load and move that load forward or backward by changing the angle of the shearlegs (a process called luffing).
If you have two shearlegs, you can rig a line between them to support a load anywhere along that line.
If you have two shearlegs, you can rig a line between them to support a load anywhere along that line.
Shearlegs (or shears or sheerlegs) are an ancient lifting device still used today. Two logs are lashed together near the top to form a inverted vee. The butt ends are anchored in a shallow hole. A pulley is hung from the top of the vee. Guylines allows the angle of the shearlegs to be adjusted.
November 30, 2025 at 11:17 PM
Shearlegs (or shears or sheerlegs) are an ancient lifting device still used today. Two logs are lashed together near the top to form a inverted vee. The butt ends are anchored in a shallow hole. A pulley is hung from the top of the vee. Guylines allows the angle of the shearlegs to be adjusted.
That's a gross oversimplification, of course. For more depth, start with the Wikipedia article on pulleys.
Pulley - Wikipedia
en.wikipedia.org
November 30, 2025 at 11:17 PM
That's a gross oversimplification, of course. For more depth, start with the Wikipedia article on pulleys.
As you may recall from high school, a pulley is a wheel that changes the direction of a rope or cable. A pulley can be rigged to impart mechanical advantage, making it easier to move the load, with more pulleys making it easier still. Using pulleys, a small group of humans can move massive loads.
November 30, 2025 at 11:17 PM
As you may recall from high school, a pulley is a wheel that changes the direction of a rope or cable. A pulley can be rigged to impart mechanical advantage, making it easier to move the load, with more pulleys making it easier still. Using pulleys, a small group of humans can move massive loads.
That last bit has some things that require explanation.
Mechanical advantage (MA) is the use of a simple machine (like a lever) to multiply the force applied to a load at the expense of distance over which the force is applied. From hand tools to massive equipment, it all comes down to MA.
Mechanical advantage (MA) is the use of a simple machine (like a lever) to multiply the force applied to a load at the expense of distance over which the force is applied. From hand tools to massive equipment, it all comes down to MA.
November 30, 2025 at 11:17 PM
That last bit has some things that require explanation.
Mechanical advantage (MA) is the use of a simple machine (like a lever) to multiply the force applied to a load at the expense of distance over which the force is applied. From hand tools to massive equipment, it all comes down to MA.
Mechanical advantage (MA) is the use of a simple machine (like a lever) to multiply the force applied to a load at the expense of distance over which the force is applied. From hand tools to massive equipment, it all comes down to MA.
If you want to make Mark's day, just say, "Pulleys!"
Instant happiness for the man.
We eventually worked out that we could use a set of shearlegs on each bank to support a skyline between them. A trolley suspended from the skyline with a chain hoist attached to it would allow us to move an arch.
Instant happiness for the man.
We eventually worked out that we could use a set of shearlegs on each bank to support a skyline between them. A trolley suspended from the skyline with a chain hoist attached to it would allow us to move an arch.
November 30, 2025 at 11:17 PM
If you want to make Mark's day, just say, "Pulleys!"
Instant happiness for the man.
We eventually worked out that we could use a set of shearlegs on each bank to support a skyline between them. A trolley suspended from the skyline with a chain hoist attached to it would allow us to move an arch.
Instant happiness for the man.
We eventually worked out that we could use a set of shearlegs on each bank to support a skyline between them. A trolley suspended from the skyline with a chain hoist attached to it would allow us to move an arch.
Additionally, the 67-foot arches would act like 650 lb. pieces of wet lasagna. Hmm.
I began kicking ideas around with my friend Mark (a retired firefighter who taught heavy rescue for years). He was probably a combat engineer is a previous life—he loves anything to do with mechanical advantage.
I began kicking ideas around with my friend Mark (a retired firefighter who taught heavy rescue for years). He was probably a combat engineer is a previous life—he loves anything to do with mechanical advantage.
November 30, 2025 at 11:17 PM
Additionally, the 67-foot arches would act like 650 lb. pieces of wet lasagna. Hmm.
I began kicking ideas around with my friend Mark (a retired firefighter who taught heavy rescue for years). He was probably a combat engineer is a previous life—he loves anything to do with mechanical advantage.
I began kicking ideas around with my friend Mark (a retired firefighter who taught heavy rescue for years). He was probably a combat engineer is a previous life—he loves anything to do with mechanical advantage.
For smaller versions of this bridge style, the arches are small and light enough that a crew of half a dozen or so people could move them into place horizontally and then roll them up to vertical.
The peaks of these arches would be 15 or so feet above the creekbed, making this plan unworkable.
The peaks of these arches would be 15 or so feet above the creekbed, making this plan unworkable.
November 30, 2025 at 11:17 PM
For smaller versions of this bridge style, the arches are small and light enough that a crew of half a dozen or so people could move them into place horizontally and then roll them up to vertical.
The peaks of these arches would be 15 or so feet above the creekbed, making this plan unworkable.
The peaks of these arches would be 15 or so feet above the creekbed, making this plan unworkable.