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Hello, I'm a sound artist and part of my work consists in collecting sounds in the field. I hike a lot (even multi day hikes) and I'm starting to get rid of some backpack weight. I just built a microphone stand (not a boom pole) by joining a 1,5 m poltruded carbon tube (that I split in 3 parts) with 2 ferrules (aluminium I guess), external diameter of the tube is 6mm, internal 4mm. As for the tripod, I used 3 carbon rods, 3mm diameter, 50 cm. I cut from wood a small equilateral triangle and drill a 3mm hole angles 35 degrees close to every corner of the triangle and a 6mm hole in the center. The rodes go into the 3 angled holes and the tube in the central one. The tip of the tube and the tip of each rode are connected with a tent rope, when the same amount of tension is applied through the 3 ropes, the rods curve and tension the structure, which becomes pretty stable and very lightweight, like 80 grams total vs 1 kg of my usual manfrotto stand. That said, I accidentally destroyed 2 rodes in a fire door, they could not resist the slam! and have to substitute them. Still, I took it as a sign to improve my crazy design.. I guess I could do better by using less tiny diameter carbon tubes and rods. My questions are: I'd like the main tube to get up to about 2 meters this time and the poltruded 6mm tube that I used is too flexible, once the structure gets tensioned with the rope everything is fine but I'd like to have it a bit stiffer not to go crazy with a shaking structure till I balance it, so should I use wrapped carbon tubes instead, with 10 mm internal diameter, 12,7mm external diameter? is the wrapped carbon that you sell less flexible than pultruded? the microphones are very lightweight (around 150 g each) and the structure will be used vertical most of the time (unlike a microphone boom pole which sustains the weight of the microphone horizontally). still when I'm on my trips I could use some more ruggedness... What should I use as ferules? Would pultruded carbon tubes (10mm) be fine if used as internal ferrules or should I opt for some different joining solution (my backpack can fit max 50 cm, I have to split the tube and the rope system I use keeps everything together anyway. I see on the internet both internal and external joints, tent-tarp poles are my main reference point. I guess there's not such a big difference but I cannot understand wether poltruded internal ferrules are rugged enough. Which kind of glue should I order from your website? I can see there's 2 which would work, one seems for more flexible structures, should I go for it?? I was thinking of ordering 5mm rodes, what I liked about the 3mm ones was that they would flex a lot, widening the base of my structure, still they were maybe too fragile. what should I go for for maximum flexibility strength (ability to return to their original shape? are rods fine or should I use small diameter tubes? I apologize for the amount of questions but it's my first carbon fiber project and I could not find much on the internet, it looks like nobody cares about weight but sound operators for cinema which only use carbon fiber telescopic boom poles..
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In terms of reducing the flex, increasing the diameter will be a good method to achieve this. In terms of weight saving, you may find a better solution would be a bigger diameter tube compared to a solid rod as they can be a more efficient and lighter way to achieve the same (or greater) level of stiffness. In technical terms, a pultruded tube will be stiffer than a same sized roll wrapped tube as all the fibres are down the length hence making it stiffer down its length. However in a practical sense, roll wrapped tubes are stronger in daily usage due to some layers of the fibres going around the tube for hoop/crush strength. Pultruded tubes can be quite vulnerable to crush and splitting down their length due to uneven applied forces. Also although there is some size overlap, generally pultruded tubes tend to be available in smaller sizes with roll wrapped tubes going much bigger if needs be. You can use quite a few different materials to make ferrules. Common choices include smaller or bigger matched carbon fibre tubes, aluminium tube or solid bar, steel, some plastics and even carbon rod in some cases. Most of these materials can be relatively easily bonded into one half of the join using a structural adhesive and then can slide in and out of the other as required for dismantling. If you are continuing to use your rope system to hold it together then you shouldn't need any method of fixing them together. In terms of adhesive, a good choice in this case where you may have shock and vibration would be our ET515 Semi Flexible 15min Epoxy Adhesive or an alternative which is slightly superior for carbon to carbon (especially if excessive shock is not expected) would be our VM100 Black 10min Methacrylate Adhesive.The choice of rods versus tubes is a personal one really once you've taken into account the factors above.
Warren PenalverEasy Composites / Carbon Mods - Technical Support Assistant
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