Connecting carbon fiber rods

[checht]

Aloha,


I have 2 - 2' 15mm carbon fiber rods I'd like to connect to make a 4'.

Guessing that best method would be to epoxy nut inserts into both, and use a bit of threaded stud.

Is this a good method? Anyone have a source for the inserts? Epoxy recommendation?

TIA

[aaronji]

Ask voltronic; I recall that he made a lightweight set up using carbon fiber. Actually, there is a thread about it that you might be able to find via search.

[EDIT: https://taperssection.com/index.php?topic=201407.0]

[voltronic]

I can't help with threaded inserts, but for the carbon fiber 406x setup I made, I used super glue to fix the internal ferrules (on the advice of the kite shop where I bought the parts.

https://imgur.io/a/mGTcH

JB-Weld is many times stronger, though not as easy to work with.

[checht]

Found a great part at home depot that I think will do the trick.
It's an expansion nut, though I won't expand it much.
1/2" od drops into the rod nicely, 3/4" or so long, captive 1/4" - 20 nut at end.
Add a 2" machine screw threaded in from the back to make the 'male' side of the pair and they'll screw together easily.
Gonna use JB epoxy. The exterior of the nut is smooth, wondering if I should rough it up before gluing?
Any thoughts?

https://www.homedepot.com/p/Everbilt-1-4-in-20-tpi-x-13-16-in-Brass-Expansion-Nut-814388/204225872#overlay

[tim in jersey]

Found a great part at home depot that I think will do the trick.
It's an expansion nut, though I won't expand it much.
1/2" od drops into the rod nicely, 3/4" or so long, captive 1/4" - 20 nut at end.
Add a 2" machine screw threaded in from the back to make the 'male' side of the pair and they'll screw together easily.
Gonna use JB epoxy. The exterior of the nut is smooth, wondering if I should rough it up before gluing?
Any thoughts?

https://www.homedepot.com/p/Everbilt-1-4-in-20-tpi-x-13-16-in-Brass-Expansion-Nut-814388/204225872#overlay

Scuffing the smooth surface with a fairly course grit sandpaper will def. help with adhesion and certainly can't hurt.

[SMsound]

I have 2 - 2' 15mm carbon fiber rods I'd like to connect to make a 4'.

-overlap them by 4" (so you'll end up with 44" not 48")
-Use fiberglass tape coated in epoxy around the overlap to make the joint. You may want to slightly scuff the carbon fiber first -- someone else will know if that's correct. Any hobby shop (the kind that sell R/C airplanes) will have the materials and show you exactly what to do.

Unless of course you can find the perfect section of telescoping carbon tube to fit inside or over your 15mm rods...

I would not bother with brass or neoprene, as they are both heavy materials (esp. brass! why not lightweight aluminum at least!). If you are going to make it heavy, then use aluminum tubes and not carbon fiber to begin with.

[Ronmac]

I opted for 15mm aluminum rods from Small Rig to build a system that is easily built and packs away in a backpack or carry on. They are not too much heavier than carbon fibre rods of the same size.

https://www.smallrig.com/smallrig-Aluminum-Alloy-Rod-15mm.html

Combining different lengths with a few of the mic clamps gets you to 48" of a very stable system. I have no fear of hanging a couple Rode NTR ribbons weighing 2lbs each.

I also have 2 of the Rode Micro Boompole Pro kits that I use with my NT6 pairs. They are very lightweight and definitely more fragile that the 15mm rods, but don't allow a lot of mounting options, especially in a horizontal config.

https://rode.com/en/accessories/boompoles/micro-boompole-pro

I still have a pretty comprehensive kit of Sabra-Som rods and clamps, but it doesn't get very much use in the field after I adopted the 15mm rods as my go to.

[checht]

-overlap them by 4" (so you'll end up with 44" not 48")
-Use fiberglass tape coated in epoxy around the overlap to make the joint. You may want to slightly scuff the carbon fiber first -- someone else will know if that's correct. Any hobby shop (the kind that sell R/C airplanes) will have the materials and show you exactly what to do.

Unless of course you can find the perfect section of telescoping carbon tube to fit inside or over your 15mm rods...

I would not bother with brass or neoprene, as they are both heavy materials (esp. brass! why not lightweight aluminum at least!). If you are going to make it heavy, then use aluminum tubes and not carbon fiber to begin with.

SM-

Thanks for your feedback. My original post wasn't specific enough, apologies.

I need a setup that allows for temporary connection of the 2 pieces to make a 4' boom, then breaks down into 2' sections for travel. My use case is rock tour, often including air travel, so I need compact and light gear that sets up/tears down fast and easy.

I currently use a 15mm aluminum rod system, cheese rod, 15mm clamps and 4 shock mounts. My goal is to reduce weight and complexity by moving to carbon fiber rods, a 3-D printed mount, and many fewer clamps & shock mounts.

The expansion nuts weigh 3g each, negligible in the overall picture.

[voltronic]

Before you epoxy those expansion nuts in, I would test the entire rig carefully for rigidity, and consider reinforcing the last 6 in of your tubes with slightly large tubes on the outside to minimize the risk of them cracking due to strain. As you might be able to see in the photos I linked, that's on the bottom section of my rig, although the outer tube goes up a good 2 feet. The .308" tubes I'm using also flex a good bit under load (by design). You really want zero flex if possible, but I would still be concerned about the internal lateral forces from the expansion nuts if you ever put heavier mics on this setup. Of course, if you are using thick-wall CF tubes it's much less of a risk.

[checht]

Many thanks, Volt.

I'm not sure what constitutes thick wall, the tubes I purchased have 1.5mm thick walls.
Total mass supported by the 2' tube will be 82g, including the capsule and active cable.The majority will be out at the end. Movo windscreen would add 30g, and act as a sail in high wind, adding force/strain.

I will do a stress test prior to epoxying, and add a fan to simulate wind.

Thanks again!

[JeySonic]

You can find nut inserts at most hardware stores or online shops like McMaster-Carr or Grainger. As for epoxy, I've had good results with brands like JB Weld or Loctite Epoxy. Just make sure to follow the instructions on the epoxy packaging for the best results.You can find nut inserts at most hardware stores or online shops like McMaster-Carr or Grainger. As for epoxy, I've had good results with brands like JB Weld or Loctite Epoxy. Just make sure to follow the instructions on the epoxy packaging for the best results.

[voltronic]

Many thanks, Volt.

I'm not sure what constitutes thick wall, the tubes I purchased have 1.5mm thick walls.
Total mass supported by the 2' tube will be 82g, including the capsule and active cable.The majority will be out at the end. Movo windscreen would add 30g, and act as a sail in high wind, adding force/strain.

I will do a stress test prior to epoxying, and add a fan to simulate wind.

Thanks again!

I would call that a thick wall. You'll probably be fine.

[checht]

I would call that a thick wall. You'll probably be fine.

Appreciated!

[SMsound]

There are also ultralight aluminum 15mm rods:
https://kondorblue.com/collections/rods

Carbon is still a lot lighter, but aluminum is nice for durability sometimes.

You can also get the 15mm connectors with holes drilled through to minimize weight.