Upgraded Slackline A-Frames: New Design to Hold the Line Steady

My first set of Slackline A-Frames work fairly well. I’ve set them up and used them multiple times so far. However, one thing became clear after I started using them with people who do tricks – the ends of the Slackline are not held static where it passes over the A-Frame. This is an important feature to have: a steady, non-sliding line. I came up with a way to add the feature to my A-Frames.

IMG_2741First, I’ll describe the problem. As shown in the above photo of the original design, the Slackline passes over a piece of 1/2″ pipe. The pipe is 12″ long or so, and there is nothing to prevent the Slackline from sliding sideways (left to right). This happens predominantly when a slacker on the line does a move called “surfing”. They kick their legs out sideways and swing their feet back and forth in an oscillating motion. This action causes the Slackline to slide back and forth on the 12″ piece of pipe. The biggest downfall of this is that it abrades or melts the line just at the point where it crosses over the pipe. In addition, it makes for non-static ends on the Slackline. This is opposite of a tree-based Slackline, where the ends do not move left to right when in use, even while surfing.

The solution I came up with is fairly simple to implement. and can be made of parts from a hardware store. First, I made two of the U-brackets shown below. Each U-bracket is made from 1/2″ black iron pipe and some fittings. Each one uses the following parts:

  • four 90 degree elbows
  • two 4″ nipples (although any length under 6″ is OK)
  • one 3″ nipple
  • two 2″ nipples.

The only critical part is the horizontal 3″ nipple. The goal is to have 2″ (width of the Slackline) between the two 90 degree elbows once they are screwed onto the 3″ elbow. I was able to get the elbows to screw in 1/2″ on each end of the elbows, leaving 2″ for the Slackline. I used parts that I had laying around as well as pieces I bought at the store. Screw all the pieces together so they look like the picture below*.

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The second thing I did was drill two more holes in the top of each A-Frame to accommodate the U-bracket. These are 7/8″ diameter holes, to accept the 0.840″ outside diameter of 1/2″ black iron pipe. The holes go all the way through the plywood and the 2×6 legs – that way you can use longer nipples if you prefer (instead of the two 2″ nipples).

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The picture below shows the solution in use. The whole idea is to create a channel where the Slackline sits as it goes over the iron pipe. As you may notice, the channel I have created isn’t quite 2″ exactly in width. That is mostly because of the way black iron pipe is put together. Threads at the joints of black pipe are tapered. For industrial applications, fittings are screwed together until the tapered threads seal together. The joints are not an exact science, so the fittings don’t always end up completely seated, or even seated by the same amount. This is one flaw in my design, and it means I need to tighten my fittings a bit more (one or two turns, by the looks of it).

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In any case, the idea was to use off the shelf parts to create a steady point for the Slackline to pass over the A-Frame. Here is another picture of the setup in use.

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Of course, the length of all of the pieces of the U-brackets can be adjusted to fit your needs. As long as the Slackline clears the top of the A-Frame, things will be fine. I should probably shorten the 4″ nipple to reduce the leverage the U-bracket has on the A-Frame itself.

Hope you get the idea.

*You may have noticed that my 3″ nipple going horizontally in the U-bracket doesn’t quite look like a piece of black iron pipe. This is because I milled the 3″ nipple to remove the extra threads present once the 90 degree elbows are tightened to this nipple. You can get around this by wrapping the 3″ nipple with duct tape, or possibly by filing the threads down by hand. Otherwise, the threads will cut the Slackline and reduce its life.

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Home Made Anchors

Today I have a couple pics of some anchors I made at home. I was able to procure some 6″x6″x0.25″ plates of 6061-T651 aluminum. I cut these down into 2″ strips, laid out some hole patterns, and drilled/milled the stuff until I was left with two pieces for each anchor.

A trip to the hardware store, and I put these together using shoulder bolts, spacers, and nuts. I still need to add some sort of strap to them for connection to the tree, my plan is to sew some dog-bone style straps to one end of the anchor.

Each anchor replaces a rap ring and a carabiner, and the eventual goal is to use this type of anchor on a longer line (> 100′).

So far, I’ve made three of these, and they work great for the 50′ lines I usually set up. I don’t have a method for testing their break-strength, but calculations show they are fairly heavy duty. Here are a couple photos:

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Rap Ring Replacements

After viewing this article over on NWSlackline, I decided to try my hand at using chain links instead of rap rings in my Slackline setup. I ventured out to my local Lowe’s home improvement store and bought one foot (nine links) of 5/16″ 3900lb working load limit (WLL) chain*. Total bill was $2.89 including tax. After cutting every other link I will have 5 good links, so the cost comes out to about $0.58 per link – not bad when you compare the cost of a rap ring at $4.75 (plus tax). A rap ring weighs about 30% less than a link, which is why climbers probably wouldn’t do something like this, but chain links are perfectly useful for Slacklining.

I used a grinder and a cutoff wheel (and some safety equipment) to cut the four odd links. This left me with 5 links for use as line lockers.

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I filed down the weld on each link. As Adam points out, over time the weld on each link can cause damage to the Slackline. (Click on the picture above, and zoom in, to see the welds on the links)  Using a file, some 80 grit sandpaper, and some elbow grease I removed the weld protrusion. The following picture shows a link after the process.

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After smoothing things over with the link, I replaced two of the rap rings in my Slackline setup, one at each end. This picture shows the fixed end using a chain link instead of a rap ring. (The rap ring seen in this picture is part of the system to remove the tri-loading, and cannot be replaced with a chain link).

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For size comparison, here is picture of a link and a rap ring:

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Chain links are nearly 1/10th the cost of rap rings, and two links can eliminate both rap rings of a basic primitive setup. This saves about $9 and gets the job done quite well.

* Note: I used 5/16″ Grade 43 chain that has a 3900 lb Working Load Limit (WLL) and a breaking strength of over 11,000 lbs (52kN). You’ll also find 3/8″ Grade 43 chain available with a WLL of 5400 lbs, and a break strength over 16,000 lbs (72kN). Either of these are good choices, and both accept a 1″ wide Slackline. I stayed away from the chain with lower rating (ie. 2650 lb WLL) and went with the Grade 43. More information here.

Slackline Anchor Basics

Today’s entry includes a video below.

Today, I decided to add a video about Slackline setup. This is part one in a two part series on anchors. We discuss the anchor at the fixed end of the line (the end without the pulleys/tightening system).

Here is the short (2 min) video:

More Info:

Want to learn more about making anchor slings and water knots? Click here.

Want to learn more about Rap Rings? Click here.

Want to learn how to setup a basic primitive Slackline? Click here.

(again, thanks to Adam over at NWSlackline for these great instructional articles)

One Week On

It has been one week since we first stepped on the slackline! We took a rest day in there, and tomorrow will be our second rest day. We are learning to do this sport with bare feet and it takes a while for the bottoms of the feet to get used to the line. Our total time on the line is perhaps one hour, about 10 or 15 minutes per day. As for progress, we are to the point of standing on the line for 10 seconds or so! A helpful piece of advice is to keep the hands above the shoulders. One lady said ‘…once your hand goes below your shoulder – you are going to fall off the line.’ She is right! At this stage, it is very difficult to recover from a hand going down to your waist. We keep practicing, and I’m hoping to be able to take a step this weekend. Fingers (and toes) Crossed!

In other news, we’ve relocated the line over a grassy area in the backyard (our feet thanked us!), and I have modified the setup to include a poor-man’s pulley for increasing the tension in the line. This meant adding two more carabiners (for a total of eight), but I feel it is worth the extra money. Here is another method of adding this ability.

My solution is shown below (Click image for larger version).

MyPulleySystemEarlier, I added one carabiner and a rap ring to each of the anchor slings. I was a bit worried about tri-loading the anchor carabiners. Paranoia may drive that decision, but our trees are quite large (> 12″ diameter) and the anchors were definitely pulling on the ‘biners non-axially.

So, we are up to 8 carabiners and four rap rings total in the system. This is four more ‘biners and two more rap rings than in a basic primitive system, but on the plus side I sleep better and have more cool gear to play with! And, although it looks complicated, I can leave most of it connected, making the next set-up quick and easy.

The “pulley ‘biner” at the tree is partially tri-loaded, but only during the tensioning process. Which means this carabiner is not tri-loaded when a person stands, walks, or bounces, on the line. I’m OK with that.