Inflatable spreader bars?

[autox]

Here's another take on carbon pole tips.

You basically turn the end of the spreader in to an archer's nock. This plan will address the concerns of a nock - splitting under load and damaging the ends if you drop them.

First, cut a 1/4" long segment of insert and glue it 1/2" from the end of the tube (this makes a 1/2" deep nock). Next, glue a carbon washer over the end - https://www.amazon.com/Carbon-Fiber-...01IITBQHU?th=1.

Then cut a notch in to the end of the pole, slicing the washer along the way, stopping just at the outer edge of the insert. This is where your suspension cord will rest, like the string of an archer's bow. Adjust the width of the cut to suit the diameter of your cord. You can start by first drilling a hole across the tube to set the depth of the nock if you like.

Tie a big stopper knot in your suspension where it will sit inside the pole end to keep the pole from sliding on the cord. It'll pass through the middle of the washer when you assemble the spreader, so this will act a bit like a keeper.

That 16mmX0.5mm tubing weighs 0.9g/in and the insert tubing about twice that. For a half inch deep nock:

0.9g/in * 0.5in = 0.45g
1.8g/in * 0.25in = 0.45g
washer = 0.36g
Total: 1.26g

The material removed with the cut/drill will balance some of the weight of the epoxy and the stopper knots also weigh more than nothing. Pending epoxy, you're around 5g for the set, or 0.18oz.

For a pair of 36" spreaders w/ 5" insert, this will put you at 3.1oz - well under 3.5oz w/ epoxy.

Fingers crossed that thin wall tubing is up to the task!



For reference, the density of epoxy resin is in the range of .001 - .0015 g / mm3. A bead around the inside if the tube 1mm^2 in cross section would weight ~0.06g.

[County_mountie]

Yes, I forgot a 30d hang doubles your weight on the suspension.

12" diameter means 4x the cross section, so even at twice the load cuts the pressure in half, and gives us a 3:1 aspect ratio on the beam, and comes in around 2.5oz for a pair in 0.5oz DCF.

At 18", we only need a half psi and the pair weigh 3oz. That's a 2:1 aspect ratio and you can double the required pressure with your lungs.

No way to know but try, I suppose.

EXACTLY! No way to know unless you try....go for it dude and post some pics of your final result...I'm sure a lot of us would love to see how it works....good luck!

[Just Bill]

Great Big Dave- Excellent point!
Personally though I have some ulterior motives for different sized spreaders and don't find it a pain in the butt if they don't match.
Though I suppose backpackers in general being hyperfocused on how each bit fits into the total kit just right is perfectly understandable.

[Just Bill]

Here's another take on carbon pole tips.

You basically turn the end of the spreader in to an archer's nock. This plan will address the concerns of a nock - splitting under load and damaging the ends if you drop them.

First, cut a 1/4" long segment of insert and glue it 1/2" from the end of the tube (this makes a 1/2" deep nock). Next, glue a carbon washer over the end - https://www.amazon.com/Carbon-Fiber-...01IITBQHU?th=1.

Then cut a notch in to the end of the pole, slicing the washer along the way, stopping just at the outer edge of the insert. This is where your suspension cord will rest, like the string of an archer's bow. Adjust the width of the cut to suit the diameter of your cord. You can start by first drilling a hole across the tube to set the depth of the nock if you like.

Tie a big stopper knot in your suspension where it will sit inside the pole end to keep the pole from sliding on the cord. It'll pass through the middle of the washer when you assemble the spreader, so this will act a bit like a keeper.

That 16mmX0.5mm tubing weighs 0.9g/in and the insert tubing about twice that. For a half inch deep nock:

0.9g/in * 0.5in = 0.45g
1.8g/in * 0.25in = 0.45g
washer = 0.36g
Total: 1.26g

The material removed with the cut/drill will balance some of the weight of the epoxy and the stopper knots also weigh more than nothing. Pending epoxy, you're around 5g for the set, or 0.18oz.

For a pair of 36" spreaders w/ 5" insert, this will put you at 3.1oz - well under 3.5oz w/ epoxy.

Fingers crossed that thin wall tubing is up to the task!



For reference, the density of epoxy resin is in the range of .001 - .0015 g / mm3. A bead around the inside if the tube 1mm^2 in cross section would weight ~0.06g.

Probably best to let Cmoulder get his prototypes finished, but I do have some high hopes for the tube itself.

I'm not familiar enough with Carbon Fiber as a material... I have an impression that drilling and even cutting requires some special care not to damage the layup. And that lots of careful sanding/filing might be required. But perhaps it's not as fragile as I think.

Ultimately- I'm attracted to the simple column and bearing plate principal though. There are few things stronger than a simple tube with a cap to spread the load evenly onto the entire column.
https://1drv.ms/u/s!Apygyt54yYPwg7dfDSIXWSvE52sqyA

This means that no matter how/what angle exactly the dyneema loads the CF pole... it's first loading the pole tips which then can serve as a distribution member.
The interface of the dyneema onto the pole can change as you shift around in the bridge too... so having a tip that acts as internal plug, distribution plate, and centering device (via the spike) is a bonus IMO all around.

As I think more on it... doing an arrow knock maybe asking too much of the thin wall tube.

You wouldn't want to use a stopper knot (though I appreciate the cleverness of the thought).
Knots in amsteel/dynaglide reduce their strength; it wouldn't be needed regardless.
In the case of an end bar bridge- the webbing loop serves as a stop on one side, the angle of the dogbone running on the other would pin it in. Other than very heavy wind just the weight of the bridge/quilts would put enough tension on it to hold.

In the case of a recessed bar bridge- you could just put it in the eyesplice.

My experience thus far- regardless of materials- is that the diameter of the tube is what is important.
The .490" tube topped out at 26" long to hold 200lbs.
Jump to .625" and you can slap a joint in the dead center of a 36" pole and go close to 250lbs.
Push that .625 up to a single joint 43" pole and you're down to about 180lbs max.
Jump to .75" and you can easily do that 43" single joint pole to 400lbs.

The .75" actually reduces wall thickness to .8mm vs .97mm on the 5/8".

The caveat of course is that is in MY bridges. Not so much to pump up my already large ego... but to emphasize each bridge is different and I went out of my way to reduce the load on the poles.
On an end bar bridge the load is higher than a recessed bar bridge. Other than Grizz and MYOG folks... I'm the only one that makes a recessed bar. So there is some concern there. Cmoulder has one of my end bar models... but it is a fairly well balanced end bar at least.

On the plus side... I'm guessing that the next bump or two in diameter (in a thin wall) will not come at a massive weight penalty if that is needed.
Also... as Cmoulder and I were joking earlier... most of the SUL speedy folks are in the 150lb range and not the 200lb range.

I'm also playing with hybrid versions of all my bridges. I was able to cut about 15% out of the Luxury bridge.
In a medium sized recessed bar bridge- that means roughly:
The Happy Medium in Hybrid 1.7 fabric is 17.125 ounces. 85% of that would be- 14.55 ounces.
The Happy Medium in Hybrid 1.2 fabric is 13.125 ounces. 85% of that would be- 11.15 ounces.

Now that's with a 5.5 ounce CF pole set. Slap in Cmoulder's 3.5 ish set and you'd be at 12.55 for a 200lb rated full size bridge and 9.15 ounces for a 160ish rated full size.

I also have a semi-recessed bar idea modeled after the micro bridge, but with 36" bars in the pile to try.
I estimate that to come out at 12.25 ounces in Hexon 1.6.
If that worked, and Cmoulder's pole worked... you'd be about 10.25 ounces for a full sized 200lb ish rated bridge hammock. (Same weight as my production micro).
Not quite the world record... but for a model actually sized for comfortable fast and light it would be pretty impressive.
Unlike the model Cmoulder currently has... I believe I can shoehorn this back into a roughly 9'8" apex to apex distance. Meaning it fits under a 10' tarp, not a 12'.

If that worked... that would be the harmony bridge I've been looking for to build a SUL kit around.

[cmoulder]

I plan to work on the 16mm spreaders tomorrow and test drive Saturday morning. Supposed to be a bit warmer tomorrow in my "shop," which is the small deck on our condo lol. Today was a good day to stay inside and continue with spring cleaning... stripped a wood floor and was reminded what a major royal PITA that job can be.

It is interesting that 16mm is 0.63" and to me it just "felt" right for this application, so it's nice to get some reassurance based on experience with 0.625" that it has some chance of success. And for no particular reason — again, just a feel for the material — it seemed that 16mm was about the smallest diameter I'd want to use with the 0.5mm wall thickness.

Am I remembering correctly (maybe from my cycling days of yore) that there was once a "beer can rule" regards to tube wall thickness... something like wall thickness of no less than 1/50th the tube diameter? Ennyhoo, this is 1/32nd, so if such a guideline exists we're well within it. lol. I hope.

[Just Bill]

If you've got some 2" PVC or similar around- I use hunks of that when testing questionable poles.
Ideally a few inches shorter than the pole. If it snaps that catches any flying debris, and if it's flexing a ton you can hear it tapping the PVC.

Though with my first test of a questionable poleset I tend to put a trusted pole in the head end, the test pole in the foot end, and just sit down and eyeball it.
Sometimes I put a ruler and a bit of blue painters tape on one side just to see if there is any flex going at the joint I can't visibly see if it passes the sit test.
Once things seem promising at the foot end, I'll sleep on it for a bit. If all goes well- then I try it on the head end the same way before I trust the set.

A bit cautious perhaps... but thus far the only time I've ended up on my *** was when I was testing 3/4" grosgrain for a tree strap and got punched in the face.

I've snapped a few poles but by taking that slow approach I've never had anything dramatic happen.

[cmoulder]

Thanks, a couple of good safety ideas I hadn't considered!

[cmoulder]

While waiting on the tip assemblies to cure a bit, thought I'd post an update...

Projected weight of spreaders without tip was 2.8 oz, actual weight 2.91oz, so pretty close to estimate:


Joiner ferrules came out really neat, good snug fit:

[cmoulder]

OK, final weight 3.588oz (101.7g)



Weight of tips 0.66oz (18.7g):



Will they work??

[GreatBigDave]

@cmoulder, I'm curious; how do you cut / finish your SF tubing?