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A-Frame and Concrete Anchor Construction Primer
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crappyslacker


Jul 12, 2006, 9:07 AM
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A-Frame and Concrete Anchor Construction Primer
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I am certainly not an slackline expert, but wanted to add my 2 cents to rigging an A-frame setup. I had trouble finding info on a-frames and concrete anchors, so I'm hoping this will help others that are in the same boat I was. These two sites had some great examples, check them too!
http://forum.slackline.com/gallery/set
http://www.slacklineexpress.com/notrees.htm

We used a post hole digger to make an 18 inch bell-shaped hole. Use a 5 gallon bucket to measure how much dirt you take out, so you can refill with that same amount of concrete. A bag and a half of concrete filled these holes, but I would recommend a slightly bigger hole, 2 bags of concrete. Ours are holding, but I'd feel better with 2 bags. Chain is hung using a stick through the last link. Leave that last link loose above the surface of the concrete, the next chain half submerged. Make sure the stick you use to suspend that last link is perpendicular to your eventual slackline - this will keep everything level. Also, in hindsight, getting 4 foot long chains and having two exposed links like on the slacklineexpress site would be a good idea for redundancy. The chain I used is 10k lbs test, and we've had two people on the line at the same time 280 lbs with no problems so far. If you're going through all this trouble, though, may as well add a little safety in there!

http://www.rockclimbing.com/...p.cgi?Detailed=75854

I built the a-frames out of the following:
2 8' rounded landscaping timbers (3'6" bases, 12" tops)
2 2x4's (24" uprights)
Half sheet of 3/8" ply for braces
3/8" threaded rod
16 nuts and washers

They were built so the line would be roughly 24" high - so the line wouldn't smack my package, but it still happens, and I would have liked a few more inches in line height. The line needs to be really tight at 24", and still bottoms out when I bounce with my 170lbs on it.

http://www.rockclimbing.com/...p.cgi?Detailed=75856
http://www.rockclimbing.com/...p.cgi?Detailed=75851

I know, I know, there's a ratchet on this rig... Done laughing? At the park, camping, etc, we use an Ellington or a 4-binner as show in coldclimb's tightening post here:
http://rockclimbing.com/...les/index.php?id=189
We found that on the a-frames it was hard to get the line tight enough, even at 25 feet between frames, with a binner based system. We tried with just the ratchet, but the line stretches so much that the spool on the ratchet fills up with the 2" webbing and won't go any further. So, using an Ellington to get a lot of the stretch out of the line, then using the ratchet to get it really tight. The ratchet also makes it's very easy to adjust it for different tensions for different people. If I had $160 doing nothing I'd buy an SBI, the ratchet was in my garage. It's not in the walking line, and it's worked very well for us!

The whole rig, 25' of walking line...
http://www.rockclimbing.com/...p.cgi?Detailed=75853

To show the amount of deflection, here's our friend Dave, was balancing in 10 minutes, was walking from one A-frame to the other within an hour!
http://www.rockclimbing.com/...p.cgi?Detailed=75857

Hope someone finds this info useful!


Partner slacklinejoe


Jul 12, 2006, 10:16 AM
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Re: A-Frame and Concrete Anchor Construction Primer [In reply to]
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Nice details.

As a possible improvement, try just using the 1" main line in the ratchet and forgo the 2" all-together. You should be able to make two piles of the 1" on the ratchet so you should be able double the slack you are pulling in and reduce complexity at the same time. To do this, start off with the main line around 1/8" from one side of the ratchet's take up spool, start ratcheting until it holds the line, then angle the side that is just extra slack towards the other side and keep ratcheting until it starts making two piles - one for the side that is tightening the line, the other for the slack side.

That should be good for a line around 40 feet long.

Cheers.


crappyslacker


Jul 12, 2006, 12:58 PM
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Excellent idea, I never did actually try putting the webbing into the ratchet. Is that how your instructions read for your kits?


Partner slacklinejoe


Jul 12, 2006, 1:05 PM
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In reply to:
Is that how your instructions read for your kits?

Only with more words and pictures :lol:

We also have other gear that gets rid of the limitation on how much slack ratchets can take up - but you're probably good without resetting the bite on a line of that distance.


uncleslackline


Jul 12, 2006, 7:46 PM
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Re: A-Frame and Concrete Anchor Construction Primer [In reply to]
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Hey Crappy
I think you must have missed the "a-frames and dawgs" down load at http://forum.slackline.com/modules.php?name=Downloads&d_op=viewdownload&cid=2
It contalns all the beta on how we do it out west!
Looks to me from your picture like your dawg is on the move already!!!
You youngsters underestimate the amount of force you are going to be excerting jumping up and down on a slackline for any length of time!
Yes, I too bell my dawgs but I use more like a wheel barrel or two of concrete with a rebar cage that I then tie a 5/8 dia. I bolt to. I also use two of them to distribute the forces.
Your a-frames are cool, you rounded the edges of the header, but if you have some wild surfing going on those bolted joints will loosen up fast!
Crappy, you have obviously put alot of time and effort into this set up! At this point in your career you need to make the investment in a set of pulleys!
You my young brother are ready!


crappyslacker


Jul 12, 2006, 8:18 PM
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Uncle,

I did indeed miss that download! Which is why I filled my dawgs with a bag and a half of concrete instead of a wheelbarrow full... I suck...

I actually have some experience with rebar, but for some reason I didn't make a cage, and used chain for my anchor... I suck some more...

We love the rounded landscaping timbers, and will use them in "A-Frames 2.0"! They're easy on the webbing, and they're easy on your feet when your standing on them! I check my nuts all the time :-) and they're still tight. I'll add a second lock nut if they tend to loosen, but you're right, I still suck...

I can't help but think that this banter is good info for those of us that don't have great trees in our yards! I did what I thought was best, learned some stuff, and you guys are adding on to that! That's what this forum is all about! And, yes, I still suck - whydaya think I'm called crappyslacker???
Thanks for the comments - I'm certainly learning from them!!!


uncleslackline


Jul 12, 2006, 8:53 PM
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LEARNING is the key word here!
I do not believe that you suck.
I say Crappy Rocks!!!


crappyslacker


Jul 12, 2006, 9:07 PM
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Crappy Rocks! Sounds like an awesome name for a band!

I truly appreciate the compliment!


slackinjacklyn


Jul 13, 2006, 6:15 PM
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I have a similar setup which I really like for the permenant lines in my backyard, except I use tree stumps instead of a-frames, I think they look better as they are basically permenant backyard furniture (typical is a 32" high and 32" diameter stump purchased from a local saw will, totally stable and bomber). They also make great starting and ending platforms. Chainsaw a rounded notch at the edge to run the slackline through. I like the hidden concrete anchor and chain thing because you can place your lines anywhere. I used (2) 80 lb bags per anchor, bell bottom hole, 3/8" chain threaded with several 1' rebar sections, no troubles yet. Also I use 3" heavy duty ratchets which seem to work fine, they have a long enough lever arm to get a line really tight (and change the tensions if you want). Plus I really don't know how to set up a pulley system anyway (I'll have to learn that someday). Anyway, I have 4 lines (30', 43', 70', and a 131' line which is 42" (darn big stumps) off the ground (I weigh 165 lbs) strung with that type 18 webbing which I love, very lively.
-Terry


crappyslacker


Jul 14, 2006, 5:45 AM
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I really like the idea of stumps! Not as portable as a-frames, but we've never brought ours anywheres anyway!

You must have a big yard to match your big stumps - 131' line would put me into my neighbors living room!


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