Cheap and easy carbon fiber marlinspike pins

**themicahmachine** · 08-17-2015, 23:44

Yes, you can find sticks for this and make the weight 0g. I prefer not to use sticks to save wear on my straps.

So one of my other hobbies is aeromodeling, and I had a bit of leftover carbon fiber pultruded rod laying around. The stuff is .188 OD, .122 ID, high modulus CF. It's cheap too! $2.90 for 2 feet: http://www.cstsales.com/Carbon_Fiber_Tubes.html Good hobby shops have the stuff. Cut it into lengths about 5 inches or whatever feels right, then put some epoxy inside the tube and on the working end of some short locked brummels in ZingIt. My total weight ended up being 7g and I went a bit heavy with the epoxy... even the most sincere weight weenie shouldn't have trouble with that. The loop end of the ZingIt goes right inside the whoopie sling loop, or can be lark's headed to whatever, to keep them from getting lost.

They're tiny though - are they strong enough? Let's see:
cross sectional area is .11in^2 in double shear, ultimate load at 6ksi for carbon pultrusion, plus the knot applies the load at about 45 degrees to the axis (probably less) so roughly 1320lbs ultimate load, each, in the worst-case loading.

**geneaut** · 08-18-2015, 07:58

I like it. it's always good to have a source for the 'obscure' parts we use in our hobby.

WV · 08-18-2015, 10:12

When you said "rod" I thought you were onto something, but you described pultruded carbon tubes. If the ones you used had thicker walls than the typical carbon fiber arrow shafts, then they are probably fine, but arrow blanks have been reported as too easily crushed by marlinspike hitches. The carbon fibers run lengthwise in pultruded tubes, so they're not built to resist those forces. Wrapped cf tubes are apparently stronger, but they're more expensive. Still, the fact that your .188 od tubes are a bit smaller in diameter than the arrow shafts that I've used, may mean that they resist crushing better. I really like the way you've rigged them with zing-it tethers. I've used similar tethers with toggles made from aluminum arrows or tent poles. Please keep us posted on how they work, and maybe consider doing some destructive testing. I agree that having ready-made toggles attached to tree straps beats looking for trail sticks. Setting up and taking down my hammock are processes I repeat enough that I appreciate anything that improves efficiency.

**themicahmachine** · 08-18-2015, 12:53

I have hung with them, and had my 40lbs daughter in the hammock with me, so a combined weight of 260lbs. No issues. These are much tougher than carbon arrow shafts - they are quite impossible to break (or even visibly deform) by hand. The marinspike hitch applies a bending moment to them really, since the webbing deforms with the toggles. In bending, pultruded carbon is very strong. If you look at the load paths involved, however, a PROPERLY setup suspension will have almost 100% of the load going into the strap. The toggle just keeps the strap from coming untied and doesn't see the full load from the suspension so long as the sling is run around the knot, instead of around the toggle. In this case the calculations put the toggles as failing LONG after the straps and amsteel whoopies have failed.

Look at the aluminum arrow shafts some use - that's very thin walled aluminum. It will crush with hand pressure, and as soon as it deforms it loses basically all of its strength. Certainly don't use something like these carbon toggles if your life depends on them holding, but if you're only risking your comfort and a bruised bum, I have no issue trusting them to higher loads than I would trust my hammock.

And you're right, I said "rod" but I meant "tube" - it was late. I also made very shorthand calculations but the margins are so high I don't see any need to worry about it.

**Squishy** · 09-04-2015, 22:03

I too hung on some carbon fiber arrow toggles I made with my other hobby being archery with my compound bow.
Proper and improper MSH usage, along with just abusing one with a 54" pry bar and mule tape with over 1000 lbs using a lever type system that cut the Muletape before breaking anything, also hung a 350 lbs or so transmission on a single toggle over a weekend with no breakage.
Arrow used was a Maxima Blue Streak 250 0.290" diameter, I also tried with 550 cord but contrary to my previous thoughts, the stuff really isn't all that strong. Neither the Muletape nor 550 caused any form of deformation any of us could see by eye.

The handful of pairs I have now are about 2.75" long but vary a smidgen as I'm not very OCD. If there is an interest in them, I can make many many more of them and send them out for a couple of bucks a pair, and just donate what's left after postage back into the forum.

WV · 09-05-2015, 06:27

Good for you, Squishy! Testing materials and sharing the results helps us all. I sometimes use a MSH with 7/64" amsteel or 2.2 mm dynaglide, though mostly with 1" tree straps. I wonder if the thinner cords put more pressure on the toggle.

**Squishy** · 09-05-2015, 06:43

Going to work soon. I'll try with some more 550 and see how little of a surface area I can cover on the toggle. I'm actually thinking the smaller the cordage the stronger the toggle will be as the section trying to bend will be shorter, like playing pencil break.

**Squishy** · 09-05-2015, 08:08

http://imgur.com/dZL5mN8
Not pictured is where I lowered it down to just above the ground and stood on the case, so somewhere around 500 lbs before the 550 frayed and ripped. If I get the chance before getting off work today I'll try to pick up the back of a truck on one with some Muletape on the trailer hitch.

WV · 09-05-2015, 08:27

Ahh! In your photo the arrow wasn't in sharp focus, but it looked like it might be spiral wound instead of having just straight carbon fibers, so I looked for more information on Maxima Blue Streak 250 arrows. No wonder they aren't crushed by the MSH! Good choice.