The suspension bridge needs to be anchored into the hillside, so we built this suspension anchor from 2" shd80 black pipe. I mitered the ends with a hole-saw on the drillpress and Davis welded the frame together. Even Danica got to learn to weld!
Time to make the bridge!!!
The suspension bridge needs to be anchored into the hillside, so we built this suspension anchor from 2" shd80 black pipe. I mitered the ends with a hole-saw on the drillpress and Davis welded the frame together. Even Danica got to learn to weld!
The cables (4) will be mounted to the back of the suspension anchor into eye-eye turnbuckles. These are attached to the anchore with 1/2 coldrold steel mounts. I broke two bench vices hammering these mounts with an 8lb hammer, before I wised-up (Davis's suggestion..) and broke-out the torch to heat the metal first. The lower cables are mounted with the simple steel loops, but the upper two come in at an angle that would just pull the loop off the pipe. So I fashioned a more complex mount (on the glove) which bites into the pipe when pulled up. These where all set in place at the right position and angle, and welded to the rear pipes. I then took every piece of scrap rebar I could find and welded it into a cage at the base of the anchor. Marlen and Davis are here attaching straps so we can move this beast.
It weighs several hundered pounds so the tractor was the only reasonable tool for moving it down the hill, and into the hole.
Roughly placed in the hole, Davis and I dream of a suspension bridge.. Both the upper and lower cables are 3/8 7x19 galv. aircraft cable. Davis climbed up to mount the upper two onto one of the existing Garnier limbs. The lower two are loosely attached at the deck level until everything is square.
Once the forms were in place, we sweated to get the anchor level and square, then poured 4.25 yds. of concrete to hold the anchor down. Here's a pic after the forms were removed, and a shot from the treehouse anticipating a bridge.
With the anchor in place we could then begin assembling the bridge. Here are some shots of how the lower two cables are mounted to the black oak. The cables are routed through the beams, attached to eye bolts, then looped loosly around the tree as a safety measure.
There are 19 crossbars mounted on 2' centers with room at each end for cable adjustments. The bars are 1" square steel tubing. Davis drilled all the holes for the cable clamps and carrage bolts, the tooling holes were plasma cut in the tops above the cable clamp holes. To prevent corrosion, the crossbars were then all hot-dip galvenized. The first crossbar was mounted at the edge of the deck to measure the cable allignment so all the cable routing holes and eyebolt holes could be drilled. Then with the lower cables mounted, the rest of the crossbars were mounted.
Okay, this wasn't too smart (but what about this project is??). But with the crossbars all mounted, who could resist the first walk across the bridge? Davis and Dottie are also seen here prepairing all the hardware for the verticle cables.
Next came the bridge decking - cedar 2x6s. Each of the deck boards had 3" routed grooves cut on 2' centers where carrage bolts were used to mount them to the steel crossbars. Davis came up with a jig design to make the router cuts centered, straight, and clean. The deck was mounted from one end of the bridge to the other, with the verticle cables mounted along the way.
A major milestone: the ladder to the deck was removed!! We now had bridge access to the treehouse!!! We let the boards settle for a week to take on the curve of the bridge, then Davis and his cousin Grady tightened the carrage bolts. Adjusting the cables is like tuning a piano. It seems I can find different tunnings which work differently for how many people are walking on the bridge. I then mounted stops at each end which the decking rests on. This seems to dampen the bouncing considerably and also shifts the resonance as you reach the ends making the bridge feel much more smooth and stable.
Next, the stairs were built at the bridge entry. You can see the first posts for the deck railing installed here as well.
