I’ve got a sporting goods application I would like to attempt. I don’t know if any of you are climbers, but I would like to do a material replacement for a climbing stopper (also called a climbing nut). If you don’t know what it is, here is one that is made out of aluminum with a steel wire: Climbing stopper/nut
So I’m looking to replace the aluminum “head” of the stopper with a carbon fiber composite. I’ve asked all over with prototyping companies that make prototypes out of carbon fiber and they said they could do it, but even for the small part i want it is incredibly expensive (a stopper is about 1/4" to 1" depending on the size, and I’ve been quoted at around $500).
So is there any way I could do this myself? I’ve watched lots of tutorials on lay-up methods, but I can’t find anything for making a more complex part. Or, does anyone know of a company that might make me 2-3 of these for less than about $250?
I’m a climber and do composites. The advantage to aluminum, brass, and copper is the material has some ductility. Composites have none. Also, carbon when abraded and abused gets little sharp pokey bits that will get stuck in your skin when handled. A carbon nut after some time will just be a wad of sharp fibers at the end of a loop of cable…that has little structural capability. Nobody, professionally at least, will make 2 or 3 for $250. The cost to build molds and develop a fabrication process will cost well into the thousands.
Brass and copper nuts have their disadvantages though in the ductility department. Use any brass nut (I currently own the DMM Brass Offsets) and you’ll see that they just don’t last that long if you are more than just a weekend warrior climber.
This will mainly have an aid climbing application where weight savings is everything. As for just trad climbing, well it’s possible but that’s not where I was headed with the idea. It actually HAS been done before (google Coyote Mountain Works Samson nut) and was headed in the right direction before the guy who made it just disappeared. There’s a really interesting back story to that which has no relevance to this post. But it actually did quite well and was more durable than you would think. The same guy, Peter Taylor, actually made an all composite cam too. In terms of polymer nuts there have been 7 as far as I can tell over the years (only one is being use currently out of nylon 6,6)
For full production scale compression molding would obviously be the most cost effective option. But is there not a way to just simply machine it? It’s not exactly a complicated design, it’s basically just a glorified wedge.
Yes, but the prototype I would be making won’t be used for climbing. I’m going to use it as a presentation piece and then after that will be pulled tested to failure on an Instron.
Ok so I don’t know why but I just wrote you a long reply and it failed to post. But in short, I know that it would have to be compression molded for full production scale, but could it not just be machine from a quasi-isotropic plate/panel? That may seem like a dumb question but I’ve never dealt with carbon fiber before. I actually work as a metallurgical engineer.
The advantage of brass nuts ISN’T the ductility. That’s actually a huge disadvantage, the durability for its application is just dead awful. The reason nuts are made out of brass is because the wire can be molded into the nut, making the part lighter because you eliminate the swage and allowing micro nuts to be made that can’t be made out of aluminum. Aluminum definitely serves the purpose well (once again, not because of ductility but because of its weight compared to the old steel nuts). My application was going to be as an aid nut. Weight savings in aid climbing is everything, and when you’re dealing around a 50-70 pound aid rack, the weight savings that carbon fiber could provide would be great. I mean it is still a prototype though, so we’ll see.
Believe it or not, this is not an original idea. It’s been done before by a guy named Peter Taylor, who made an all composite cam and nut. The nut worked great, but the cam was a failure because the stem broke (you can imagine how a cam goes over some edges, there would be no strength along that axis in carbon fiber). Basically there is a long back story, but after the stem snapped in testing Peter Taylor was never heard from by the person he was presenting the new gear to and that was the end of the carbon fiber nut. My point is though, it’s been tested and it’s performed decently well.
Hardness, toughness, and ductility all play a roll in the durability of a nut. Every time the nut is placed and removed some part of the surface/shape undergoes plastic deformation. These can be scratches, dents, etc. While some of the material gets removed with use, most of the material stays intact (though deformed). This will not be the case with a carbon nut. You will lose portions of the matrix (resin) which holds the fibers together with every placement due to it’s lower ductility and toughness. The fibers may remain but the resin will fracture leaving unsupported stray fibers. They may work for a single speed ascent up El Cap but they would have a very short life and be significantly more expensive. You could possibly use some type of fiber reinforced thermoplastic but these would be nearly impossible to get out once they are set.
A plastically deformed nut means it was not durable enough to handle the application (save for the brass micronuts, I’ve seen some pretty crazy deformed brassies). Scratches and small dings like that are normal, but if a nut deforms to where the original shape and structural integrity has been compromised then somewhere, something has gone wrong in the manufacturing of that nut. You also have to have one hell of a fall factor to cause a nut to deform like what you’re talking about.
Having said that, you do present a good argument about the resin chipping away. I wonder whether it would cause much durability issues though. There isn’t really an impact/shock force, so the brittleness of a carbon fiber composite may or may not matter. It’s already in contact with the rock in a fall, it’s not like the nut is smacking the rock. So it would be interesting to see.
As for fiber reinforced thermoplastic, I’m not sure about fiber reinforced but there are already plastic nuts being produced (and have been produced in the past) made out of polyamide that aren’t reinforced with anything at all that actually have a really good durability (check out gear4rocks, I’m not posting a link because I don’t want my post to show up a week later because it has to be reviewed). They actually seem to hold up better than the brassies.
So back to the question I asked before, if a get a cured prepreg quasi-isotropic plate/panel would it be possible to mill a nut out of it on a CNC or manually?
Only if the panel is thick is enough. You will want the fiber plane to be perpendicular to the the length of the cable. If the fiber plane is parallel to the cable then the cable will just delaminate the plies.
For the machining idea, couldn’t you just lay up a number of plies to get the rough desired shape, infuse with a PU for ductility and weight savings and then machine to final dimensions? I mean, it really doesn’t have to be that strong compared to ductile since you are looking at it as an aid device. BTW, I have been climbing for almost 20 years just for a point of reference.
Exactly what I thought. Injection moulding in silicone moulds. But I still have no clue of what the thing is used for.
The only climber I knew climbed freestyle: Just a bag of magnesium, good shoes, and up you go. No safety, nothing. (he eventually died doing another extreme sport: freediving). This guy actually was building 2 catamarans of over 18 meter long (60 ft)
