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How to make Gymnastics/Fitness Rings from PVC Conduit

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Here is how I made a set of fitness rings using grey Sch 40 PVC conduit. I was inspired by this Instructable and various comments posted on it:

http://www.instructables.com/id/How-to-make-PVC-gymnastic-fitness-rings/

Rather than using regular PVC pipe, I decided to use grey conduit as it is designed to be bent when heated up. I also used fine-grained "play sand" because it can be compacted better than most sand you would find on the ground (unless you live at the beach), resulting in fewer air pockets and presumably a reduced chance of the pipe kinking. I have a small oven that is not large enough to fit the lengths of pipe so I describe the steps to compensate for that.

Overall, this process was much simpler than I had anticipated. Once all the materials were in-place, it only took me about an hour to actually make the rings and they seem very strong.

Step 1: Get Materials

Materials:

2 x 27.5" sections of 1" diameter grey rigid schedule 40 PVC conduit (Home Depot)
2 x 12 foot lashing straps (Harbor Freight Tools $3.99)
wire (if your oven is small)
Gorilla Tape (or duct tape)

Tools:

PVC pipe cutter (or hacksaw)
tape measure
an oven
a 9.5-inch inner-diameter cylindrical object (like a bucket or a trashcan)

More information on bending and cutting PVC pipe can be found here:
http://www.backwoodshome.com/articles2/sanders94.html
 
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scrapperzen2 years ago
"you didn't list any warning with the straps...waaaahh!" I honestly can't believe people are arguing with you about static vs dynamic loads, with one member challenging you to perform complex gymnastic moves with these. I'd suggest those guys go have fun with a slide ruler and leave fitness stuff to others.

These rings are awesome. I've put together several pairs over the years and have never had any problems with them whatsoever. Pullups, muscle ups, dips, pushups, pronated knee tucks. Same PVC tubing and cheap auto tie downs.

unjust5 years ago
well done, but the buckles on those straps are not designed for that kind of load, just a static force. you'd be far safer with a stitched loop or rated rope. when those buckles fail, it's usually non passive. i'd also be concerned about wear on the webbign from teh ends of the plastic, maybe flaring the business ends of the tube outward to give the rope/strap a fillet to move against.
Mr.F (author)  unjust5 years ago
Each of the straps is rated for 1000lbs static load. It says not to exceed 1/3 of that load but that is so that if you tied down a load on a truck and you stopped suddenly, then the force on those straps could become close to 1000lbs pretty easily. Since they are only supporting my body weight, even if I bounced up and down I don't think I'd come close to that. I didn't document this because I wanted to find a better solution but if you look closely at the photos, you'll see that I added a strip of gorilla tape to the ends so that it doesn't fray the straps. The straps were so cheap though that I figured I'd just replace them if they started to fray. I'm thinking I'll try feeding loops of rope through the rings like the other Instructable so that the rings don't flex as much. The amount of flex is still minimal but I'm afraid that over time the conduit might develop cracks at the ends from flexing. Thanks for the comment!
unjust Mr.F5 years ago
you are not applying a static load unless you're *only* hanging from them.
if the working static load is ~330lbs that's fine, however i assume you intend to swing and do pullups and the like from these. that's a *dynamic* load, and not something the buckles are designed for, and something you don't know the webbing rating for.

there's a decent chance these will never fail for you, however your gear does not produce a system that is designed to sustain a dynamic load, and that's not a safe thing. if you read the package of your straps i'll wager that there's even an explicit warning along the lines to not to use for lifesafety uses or to support people.
Mr.F (author)  unjust5 years ago
I'm sorry I don't think I was clear enough. Look at this link:

http://www.bstorage.com/speleo/Pubs/rlenergy/Default.htm

In it, it states an example:

In the example of Figure 1, a 180-lb person takes a 5-ft fall, yielding 900 lb-ft of energy. From the graph we see that this energy results in a load of about 1900 lbs and a rope elongation of about 1 ft. This exercise shows, without the use of equations, that the dynamic loads on ropes and belay anchors are the consequence of rope characteristics.

I weigh 150-lbs and each strap I have is rated to support a static load of 1000 lbs. Since there are two straps, given I applied equal force to both, together they can support a static load of 2000 lbs.

If I weighed 180 lbs, let the straps slack 5-feet, held on to them, and jumped off of a ladder, these straps would be able to support that. My arms would undoubtedly be dislocated if I hung on. Since nothing I will ever do on these rings will come anywhere close to that, I deem the straps to be safe.
unjust Mr.F5 years ago
no. static load != dynamic load. you'll notice that dynamic load ropes are rated in newtons, not in pounds. force is not the same as weight/mass.

look at the packaging for your straps, or even a little warning tag on the strap themselves and tell us that no where on it does it say anything about using it for supporting people, climbing or the like.

you're also not addressing the hardware, the clips. those are not designed to maintain on a dynamic load. something like a locking carabiner is.

as i said, you'll probably never have an issue, BUT, you have not designed a system that is safe. (or as safe as an engineered system designed to support a moving body ever can be)

brilliant use of molding for forming the pvc though. and well documented instructible.
Mr.F (author)  unjust5 years ago
I never claimed "static load == dynamic load". You can compare them if you look at the maximum amount of force that would be exerted on them.

pounds = mass x acceleration due to gravity

Pounds and newtons are just units of force:

http://en.wikipedia.org/wiki/Newton

Dynamic loads need to account for possible acceleration greater than the force of gravity, such as putting on the brakes on your car (see the first paragraph of my first response). That's why these straps state that a static load is not to exceed 1/3 of the maximum force of 1000lbs because of the fact that accelerating and decelerating could cause the load to exert more force (presumably, up to 1000lbs in most tie-down situations that these straps were designed for).

My own link, in the section you described, concludes:

"The probable end result is that there is a negligible reduction in chance of rope failure and a significant increase in chance of victim injury from high deceleration loads."

as a result of making stiffer ropes. They are actually stronger but can cause someone who is belaying to decelerate faster, increasing the risk of injury or death. As they say "it's not the fall that kills you -- it is the sudden stop". They were trying to say that "shock strength" is misleading:

"Probably the most harmful result of this situation is that "shock strength" has encouraged us (and equipment manufacturers, through competition) to make everything stronger."

As for the clips, they are designed to hold alot of force when pulling the strap parallel to them (which is where most of the force on the rings comes from, such as for muscle-ups, pull-ups, push-ups, etc.). I would never go belaying with them obviously since the force can be exerted in a multitude of directions (which is why carabiners are used). I wouldn't feel comfortable swinging on them like a swing but I think the amount of sideways force is minimal.

It is good of you to question the safety of lashing straps for this application. I would not use them if I didn't understand why they are rated for 1000lbs and how they could fail. You bring up a good point about the clips as I'm not entirely sure how they could fail if they experienced a great amount of sideways force. They are designed to clamp down tighter when force is exerted on the strap normally. Like I said though, I won't be swinging on them like a swing -- I'll swing on them like gym rings.
unjust Mr.F5 years ago
you have a strap that is rated with a *static* load.

you do not have documentation about elongation or shock strength. various materials exhibit dramatic differences to different types of force.

if you are moving, you are providing a dynamic load. simply swinging, it'll be similar to a static load, but is not.

while you're probably not placing a falling "shock" load on them, you are not placing a simple load in one direction on them.

you have not commented on any warnings provided with the straps.

you're very probably fine. were i doing the same thing, i'd sew the straps into loops and put a rated link between them. still not a rated system, but it places stress in a known manner on a known material.

pondering this further, is there a reason to not use a length of chain that will fit through the pvc? possibly threaded through an old bike innertube to remove pinching of fingers above the pvc grips? I imagine that wire robe would wear the pvc significantly.

Mr.F (author)  unjust5 years ago
I understand the difference between static and dynamic loads. Let me ask you something: if all you had to pick from were lashing straps that were rated for a static load, what is the minimum static load amount would you be comfortable with?
unjust Mr.F5 years ago
iirc NFPA calls for 15:1 and AES 10:1 the idea is that the max load (not failure load) will gradually weaken the line, where as safe working load is what it can sustain for the life of the line. hence the bigger factor.

i've always gone with 10:1 so if it says it'll hold 1000 lbs you can safely support 100 lbs. that's with non-life safety loads, and straight lift loads.

if things are going to be dynamic, or support a person i double that, although i've *carefully* operated at as low as 6:1 for temporary purposes (a lower rated attachment while getting something properly located, or as a lift line for something that won't get hurt by the line failing, and a line that won't slice me wide if it fails) keep in mind that using multiple supports at angles changes the forces on each point, so you want to add a further derating factor, 20% at 30 degrees comes to mind, but i look that up to be certain when i need it.

again, i think your biggest risk factor in this system is the buckles. i barely trust those things when loading a truck, and when they fail, they can *launch* parts. (remember that knots will significantly weaken things, but a proper splice will do so *much* less)

your not going to be putting that much force on these rings. These are for static strength moves. I use wooden rings I made on my lathe for iron crosses and malteses. I quit gym recently and I want to keep my cross and planche.
unjust Mr.F5 years ago
your own link discusses the difference between static and dynamic load through the section on strength misconceptions, specifically the paragraph on shock strength.
svfox69 Mr.F5 years ago
Maybe have a physics professor at the local school calculate the maximum force/load put on the rings while swinging. Since you are not just hanging but using force as you move that I believe could be more than 1000 lbs seeing how strong gymnasts are.

Steve
http://scrabblecheat.com
You wouldn't want to do anything putting that much force out on these rings. Giants and bails from handstand put around one ton on the rings and cables, however, the people using these rings are not going to be doing these, atleast on these rings. First of all you need atleast double your hight in ceiling space, preferably more so you can start in handstand to bail. I would like to see you even hold a handstand. Have you ever felt what that feels like on your hands? I usualy grips, and even with them, it feels like you are going to slip off the rings if they are slick fiberglass, or plastic like these. I would like to see one of you do a bail from handstand and actualy hold on, its not easy, espicialy without grips. Video it please, its going to be funny to see you land on your head when you peel. Its happened at my gym, never to me, but to others.
gurnieBP3 years ago
my bad,i was really thinking of health,in the living section.
gurnieBP3 years ago
why exactly is this in survival,i believe it would be more appropriate in fitness
Mr.F (author)  gurnieBP3 years ago
Good point. Unfortunately, only these categories were available: Survival, Camping, Knots, Snow, Bikes, Boats, Kites, Skateboarding, Water.
 Just made a pair and they're sick. Thanks a bunch dude!
teeroy655 years ago
What temperature range did you use?
Mr.F (author)  teeroy655 years ago
350-degrees
godspiral Mr.F5 years ago
any burning smell at that temperature ?

It starts to soften at about 170F.  I'd use 300F, but if it didn'tsmell up, then ur prob fine.
burnnfly5 years ago
These are excellent. I got the materials, and were using them within two hours. I sped up the cooling process by filling my shaping cylinder with cool water after several minutes, and they totally cooled within five minutes. Great Instructions.
It is easier to heat the sand up and then put hot sand into the pipe. This can be done by putting a few quarts of sand into a pan and heating to about 350 degrees on a camp stove or on your gas range. Tape one end of the pipe as described and pour sand into the pipe. Empty the sand after about a minute. This will have preheated the pipe. Then pour sand in again, and tape the other end. In about a minute your pipe will be very rubbery. now you can bend your pipe at will. The pipe will cool quicker if you can get the sand out.
Mr.F (author)  aaronnielsen5 years ago
You don't need to heat the sand first because of the fact that conduit is designed to be heated and bent -- not like PVC pipe.
Cool, dude. I ended up suspending them from 1-ton beam clamps that you can get from Fastenal.com, which were hung on a steel beam in my boss's gym. You can also use these rings for over splits training, which, as a guy, they hurt like nothing else. Cool thought with just using the lashing straps. I really only used the rope to get more length out of the lashing straps.
rimar20005 years ago
The ends they seems to me a little weak. Perhaps bending it up and join them with duct tape or a little clamp... But if it works, go ahead! Good instructable.
Mr.F (author)  rimar20005 years ago
I was originally going to put rope through the rings and then attach the lashing straps like the other Instructable did. The way the straps are now, they apply force outward as if they are trying to turn the rings into horseshoes. I was actually surprised, however, at how strong they are. When I hang from them, even bouncing up and down, the rings remain very rigid. I weigh about 150lbs. Depending on your weight, you might want to use rope or clamps like you said. If you wanted to bend them up, then you would probably need to either punch a hole in your cylindrical mold or bend the conduit around something like a paint can (which might produce more teardrop-shaped rings). Good points!
rimar2000 Mr.F5 years ago
Hahaha! I can only watch them, do not use them. At the moment I am suffering from renal colic, and when these are removed, I hope to be able to walk ... Good work!
Mr.F (author)  rimar20005 years ago
I hope you get better soon!
Mr.F (author) 5 years ago
Thanks for the encouragement :-D
Nice! I definitely want to do this.
implaxis5 years ago
Excellent -- I've been wondering how to do this for another project!
rislejay5 years ago
Great Job!