Could use some help with a carbon fiber tri-leg stool
Aug 8, 2022 at 10:31 pm #3756847
Hey folks, first time posting. I’m really desiring an ultralight backpacking tri-leg stool. I generally push my legs pretty hard when hiking and just don’t find it comfortable to sit on the ground. On my last trip, I spent the time in camp just standing/squatting even though I really needed to rest my legs. I think I can skip the back rest as long as I can get off my legs.
It actually required a surprising number of adjustments to get a stool that works. I eventually had to drill holes in the tubing to keep the lashings in place. I wanted this thing to feel solid even though it’s very lightweight and this makes sure the pivot point does not slip whatsoever. For now, I’m using a cheap canvas seat. The problem is the canvas is heavy and it stretches. I think DCF would be superior in both ways. The total weight I have right now is 6.5 oz, but the canvas seat is 2.5 oz of that.
Previously, a couple others have done similar builds on BPL:
Chris Zimmer made this seat:
Ron Rod made this prototype:
Is there anyone interested & able to do some custom work and make a dyneema seat similar to the one Chris Zimmer made? I really have no experience sewing, especially with DCF and I just don’t think I could make one nearly as good.
Also, the carbon tubes I have are 0.5 inch diameter. They are super light, but also I think I could go lighter. They actually feel overkill at the moment.
Thanks for any/all help and advice!Aug 9, 2022 at 9:36 pm #3756942Sam FarringtonBPL Member
@scfhomeLocale: Chocorua NH, USA
Am not suited for a stool, vs a chair, but want to mention a few things about carbon fiber tubing. First, I use flexible carbon tube for tents, and have learned that the lower diameter tube is more easily crushable when force is applied to the sides of the tube.
Second, the quality of carbon tube is all over the walk, from junk sold on ebay, to cloth wrapped, to cloth wrapped with layers that run both parallel and diagonally to the tube, and Third, the highest quality is filament wound tube, which is very expensive.
Fourth, the larger diameter tube, such as those used on hiking poles, are far less prone to breakage than the low diameter; but depending on the layup, also vary greatly in strength; and the better quality should be preferable, because of the large forces concentrated at the point where the struts cross. A couple of less expensive poles I’ve used that are strong are the Cascade Designs and Yukon Charlies. But you may have already found the best source for your application.
Last, drilling in the sides of the tube would weaken it; so if you can devise any other approach, you’d have a much sturdier stool. If you cannot, reinforcements of the tube at the pole crossings with short lengths of alloy or carbon tube that slip snugly inside or outside the strut tubes for a few inches and are bonded in place. Note that epoxy can weaken carbon, so try some JB Weld first on a short piece of the tubing you are using.
For my canoe style chairs, sturdy mesh sold by most of the suppliers is great because it does not collect water, and makes for a dry seat that molds to your shape. But not sure it could be adapted to a three legged stool.
In the Scouts we learned how to lash three poles together, but this was for tables, and not sure how it would work on three struts of a small stool. Could not make out the structure of the binding exactly in the photos of your project. There are some very strong Spectra and Dyneema cords, though.Aug 10, 2022 at 5:30 am #3756955Eric BlancheBPL Member
@eblancheLocale: Northeast US
JB Weld Plastic Bonder is the new easily found go to for carbon fiber bonding/gluing, IMO.
Seat top looks easy enough to recreate. If I had more time, I would make it for you!Aug 11, 2022 at 9:45 pm #3757117
Thanks for the protip about the JB Weld, I was actually going to use Epoxy on part of it -glad I didn’t.
The tubing I’m using is some pultruded tubing from DragonPlate. It’s pretty thick, in fact probably overkill. Even after drilling holes in it and bouncing around on the stool.. it seems super solid. It is a good point though about the large forces concentrating on the pivot where the struts cross. This is where I see the slightest amount of bend forming when I’m sitting on it.
About the mesh idea, if I could find a way to attach some Cloud71 without sewing, that would be awesome. Perhaps with some kind of hammock knot around the end of the pole tips.. I’m not sure.Aug 21, 2022 at 11:27 pm #3757826
Sharing some photos of the finished product. My sewing is terrible but at least it’s functional. The carbon tubes are 20″ long and the final weight is 5.1 oz. The dyneema is the 1.43 oz/yard variant, and the actual seat weighs 0.4 oz. That’s over 2 oz less than the canvas one, and comfier as it doesn’t sag/stretch.
The other nice thing about dyneema (both fabric and the bear line) is that when you fold it into a position, it stays put, so very easy to pack and unpack quickly. Contrast to a helinox chair for example, where the setup time is a bit too much to make sense for a rest stop.Aug 23, 2022 at 2:25 pm #3757983DanBPL Member
Nice job with that project!Sep 22, 2022 at 8:46 pm #3760585
I’ve made some further modifications and the stool is now 4 oz exactly, which is 14 oz less than a similar shaped REI Trail Stool.
– Resewed the dyneema seat using a different pattern which has no high spots when tension is applied, and is also stronger because force is not concentrated at a single thread point.
– 3d printed a center pivot to prevent the legs from rubbing and hold them in position better, held in place with kevlar cord.
– 3d printed feet which are lighter and also include holes for the bear line. also tied the bear line in a different fashion which won’t ever come out of position.
– 3d printed a small clip to keep it secure for storage (1.5 grams)
-“downgraded” to cheaper, lighter, and slightly larger diameter carbon fiber tubes (shaved weight)
Some pics of the MK II..Sep 22, 2022 at 9:03 pm #3760589d kBPL Member
That’s really great! I’m so coveting that…Sep 23, 2022 at 4:33 am #3760603Kevin BabioneBPL Member
Nice work – it’s fun to see the evolution in this thread. Get ready for the PMs asking if you’d consider making and selling them…
Have you thought about a lighter version of the Helinox Ground Chair?Sep 24, 2022 at 2:46 am #3760641Jan RezacBPL Member
@zkoumalLocale: Prague, CZ
Very nice. What are the specs of the tubes used?
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