How to Build a Small Cable Suspension Bridge

As mentioned, we built this bridge and wrote a “how we did it” book about the process a few years ago. Recently, I thought it would be fun to share the basics of this design as an Instructable for people who have enough skill to be able to take the information and work with it. And as we do in our book, we recommend having your specific design approved by an engineer just to be on the safe side.

Here is the link: Building a Small Cable Suspension Bridge – the Basics Plus a Video Demo

I entered their “Outdoor” contest and you can kindly vote if you like by clicking the little vote button at the top of the instructable page. Thanks! I need a t-shirt.

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Making a Quick and Simple “Stop” for Multiple Cuts

When I’m cutting a lot of boards the same length and angle, it doesn’t make sense to measure each time, or mark multiple cuts along a single board. Employing a block stop system is not only efficient, it also allows the boss to set up a cut and turn someone loose on the task who knows how to safely run the saw and won’t have to worry about careful measuring.

Use scrap wood – 2 pieces of 2x material + a piece of 3/4” material (plus whatever needed) to create a support base that is at the same level as the cutoff saw’s base. In this photo a layer of cardboard was used under the 3/4” material to obtain the right level.

Check that the base of the saw is at the same level as the support base.

Secure the cutoff saw to the worktable. Then square up one end of a board and mark it for your proper length to be cut multiple times, creating your set-up board.

Lay the set-up board so the length mark is directly under the blade. Center the support base under the other end. Fasten both 2x scraps down securely to the work table. Leave the 3/4” scrap loose for now.

Nick the set-up board with the blade at the length mark. No need to cut it to length, you might have a use for it elsewhere.

Keeping the set-up board held securely, flush edges with the 3/4” scrap. Pencil mark the 2x support base.

Fasten the 3/4” scrap to the 2x support base at your pencil mark: the end of this board is your stop length.

Use a straight cut scrap to flush the 3/4” stop board edge with the board to be cut. Start cutting! If you are cutting angles, just make sure the top of the angle hits the stop block. Otherwise you risk undermining.

Thanks for stopping by! Be sure to check out our suspension bridge book. Here is the link:

Building a Small Cable Suspension Bridge with the Cable Locking System

Images, diagrams, and text copyright 2013-2017 by Marvin Denmark unless otherwise noted. Please do not copy and post my content anywhere without my permission. Thank you.

Adjusting a Suspension Bridge Deck

One of the hazards of building a bridge in the woods is that there are trees in the woods. And trees sometimes fall. It was only a couple of weeks after my bridge was completed that a tree fell on it. It bounced off without causing damage other than a dent in a deck board.

A couple of years ago during a flood, a tree next to the bridge came down, and while not actually falling on the bridge, parts leaned heavily on the suspension cable. I cut off the branches that were in our way and let the rest stay for now since I was busy with other projects. This spring I finally cut the rest of the tree that was affecting the bridge cable. I knew that the deck had sagged a bit and would need to be adjusted at some point.

That’s why I have turnbuckles installed on all the deadman-to-post cable connections as shown in my book, Building a Small Cable Suspension Bridge. I could just turn them to pull the posts back and level out the deck again.

I used  what was handy to provide a resistance (something to work against) to turning the turnbuckle – in this case a big stick and a metal pipe.

WD40 oil worked to loosen up the connections. They weren’t rusty having been protected under the cover of those white tubes all these years, but they didn’t want to break loose easily.

I used a small bar for turning, but a longer one could have made things easier.

I used a pencil mark to verify if I was tightening or loosening.

Once they broke loose, each turnbuckle turned easily.

Jeep seemed amused that one side was now lower than the other. But that’s just part of the process!

I worked on all four turnbuckles, using line of sight to achieve the results I wanted.

All done, until the next tree takes a dive into the creek and the bridge is in its way.

This all only took about 30 minutes. Here’s a movie of the process if you’ve never seen a turnbuckle in action.

Thanks for stopping by! Be sure to check out our suspension bridge book. Here is the link:

Building a Small Cable Suspension Bridge with the Cable Locking System

Images, diagrams, and text copyright 2013-2017 by Marvin Denmark unless otherwise noted. Please do not copy and post my content anywhere without my permission. Thank you.

Zip Line Challenge

My spousal unit, who actually writes this blog, is an author and illustrator of books for kids. She ran across this website for aspiring engineers, and thought it would be interesting to some of my readers. DiscoverE (formerly the National Engineers Week Foundation) helps to unite, mobilize, and support engineering and technology volunteer communities. They hope to increase the collaborative footprint in K-12 education and celebrate with the public as it discovers the value of engineering education and careers.

I was especially intrigued by their Zip Line Challenge for kids. It’s actually a model that challenges kids to transport a ping-pong ball down a zip line from start to finish in 4 seconds or less. The activity discusses many of the considerations when designing and building a zip line. I’ve uploaded the PDF so you can download it from here, or you can get it from the website listed above. There are a lot of other creative engineering related activities there, all free to download and use in your classroom, home, summer camp, whatever.

Check it out: zip-line-challenge_091316

One of these years I hope to finish my zip line. All is ready, but now the brush has grown up so much I have to hire a tree climber to clear the 420 foot long pathway.

View from the zip line tower to the landing 420 feet down the hill.

Thanks for stopping by! Be sure to check out our bridge book if you’re thinking about a DIY suspension bridge. Here is the link: Building a Small Cable Suspension Bridge with the Cable Locking System.

And if you’re curious about Robin Koontz’s books, look her up on Amazon as well: Books by Robin Koontz

Images, diagrams, and text copyright 2013-2017 by Marvin Denmark unless otherwise noted. Please do not copy and post my content anywhere without my permission. Thank you.

Marston Mat Mudway

Marston Mats, aka perforated steel planking (PSP), were developed by the U.S. before World War II. The idea was to quickly build temporary runways and landing strips. They were first used at Camp Mackall airfield near Marston, North Carolina, in the U.S.

A Curtiss P-40 Warhawk on a Marston Mat runway at Milne Bay, Papua New Guinea in September, 1942. – public domain

 

I honestly don’t remember where or when I acquired four of these heavy metal planks, probably saw them advertised somewhere. I know I didn’t pay much for them. The idea at the time was to see about using them for my bridge deck. I wasn’t able to acquire any more at the time, so opted for the wood deck you see in the photos. One of these days I’ll replace that deck with something metal. I like that the perforations would let air flow through so the bridge would not be as vulnerable to high wind gusts.

Meanwhile during our rainy season, areas where we like to walk get more than a little muddy. The small creeks flood and send water everywhere. I’m always digging ditches to try to control the flow somewhat, but this particular area is low, so it’s always a mucky mess.

So I installed some 2×10 planks I had as well as the four Marston Mats. Nothing much to it, other than first setting out short cross members for everything to rest on. While you could just toss the planks into the mud, raising them up a bit makes them more effective, and you can get them level to some extent. I screwed down the wooden planks, but the mats were heavy enough to be stable without reinforcement.

When finished with the project, we noticed that Jeep the dog appreciated the wooden planks, but not so much the mats. He proved the point that the Marston Mats would not be the best material for a bridge, assuming you want to allow your four legged friends to come across with you. We’ll be watching for other options.

Thanks for stopping by! Be sure to check out our suspension bridge book. Here is the link:

Building a Small Cable Suspension Bridge with the Cable Locking System

Images, diagrams, and text copyright 2013-2016 by Marvin Denmark unless otherwise noted. Please do not copy and post my content anywhere without my permission. Thank you.

Habitat for Pond Turtles: Turtle Sofas!

There’s a stream that runs through our property and into Wildcat Creek, close to where our bridge resides. Though the stream is officially nameless, we’ve always called it Phillips Creek, because it ran through the Phillip’s place; Belle’s Creek, because our neighbor’s dog loved to play in it; and Penn Creek, so named by the ODFW who showed up (without notice) to count fish one day. Whatever the name, the stream tended to cause flooding in the pasture in winter, so we put in a pond. How that was done is a blog for another day.

At first the pond dried out in summer, but once the beavers noticed it, they routed more of Phillips Creek so that it flowed into the pond year-round. We installed a bigger culvert along with a fence to keep the beavers from clogging it up, and had ourselves a nice pond we called Buddy’s Lake, after our beloved Swamp Puppy, Buddy.

We had seen pond turtles in various wetland areas on our property, but were amazed at how fast they discovered Buddy’s Lake. They first appeared on a log that we’d left out, sunning themselves in the spring chill. When that log began to sink, as logs are often prone to do, we decide to make turtle sofas.

Previously we milled up a few logs for various projects and had kept the sides for benches or whatever. So why not a turtle sofa? And to keep our sofas from sinking, we screwed on strips of rigid insulation we also had left over after building our house. The material isn’t toxic for the watershed.

After launching the first sofa, we noticed that it tended to hang out close to the shore where a turtle might feel vulnerable to land animals, especially the two-legged variety.

This turtle is game to try anything new!

So we tied an anchor to a rope attached to the sofa and tossed it out so the log would float more in the middle. We also roped the sofa to a tree on shore so we could haul it back in if need be. And, we added measuring sticks as a fun way to see how big the turtles were. A full grown pond turtle gets to be 6-7 inches long.

Jeep, Buddy’s predecessor, wonders why we threw such a big stick for him to fetch.

We added windjammers to a couple of sofas to help stabilize them. Probably not necessary unless you have beavers who like to knock them over and use for their dam.

This is a turtle favorite, probably because of the moss that has grown on it. Without the foam underneath, this old log would have sunk by now.

Six is not a crowd!

We’ve seen up to nine pond turtles at once on Buddy’s Lake. We’re happy that our turtle sofas are a preferred place for them to hang out. Or do whatever it is turtles do.

Floating Mantel Shelf

Our house has posts, beams, and siding made from Douglas fir milled on our property. I decided to employ another kind of wood for a fireplace mantel. Bitter cherry, also called Oregon cherry (Prunus emarginata) is a native tree that popped up in our woods when it was replanted in 1988. I wondered what the grain and color would look like when it was milled. It has an interesting bark, that much I knew.

So I picked a tree I liked and thinned the woods by one cherry tree. I parked it in the barn to dry for about five months, then had it milled to about a five foot 5-1/2″x7″ with bark edge on the 7″ width.

As control against splitting, I scored slices on one side in varying depths, the deepest being the middle cut over the tree center at about 1-1/2″ deep. Then I primed the sawn sides and left it to dry, standing up, for about 3 more months.

I was hoping to preserve the bark, so cutting and fitting the corners was tricky. I sanded down the precautionary slices (which were on the bottom) and cut the pieces. I sanded, splined and glued it all together, then applied a clear finish. The bark is threatening to peel, but underneath looks pretty cool so I really don’t care.

de-barked Oregon cherry

I used a bracket system to install the 35+ pound mantel. I hollowed out two slot holes at 9/16″ depth on the backside that corresponded with metal brackets that screwed to the wall studs.

Metal straps, which were recessed so that the mantel would fit flush with the wall, were screwed across the hole slots. Taping their location on the mantel top,  I could line them up with the marked brackets.

A bit of hammering with someone else holding on, and the mantel was up.

I have 3″ metal posts that I had intended to install on either side, not for support just for looks, but for now we’re seeing if we like just having a floating mantel. Eventually there will be a wall sculpture underneath. I’m just waiting for my spousal unit to come up with something…

Thanks for stopping by! Be sure to check out our bridge book if you’re thinking about a DIY suspension bridge. Here is the link: Building a Small Cable Suspension Bridge with the Cable Locking System

Images, diagrams, and text copyright 2016 by Marvin Denmark unless otherwise noted. Please do not copy and post my content anywhere without my permission. Thank you.