I am making carbon fiber pushrods with 4-40 all thread ends JB welded in place.

How far does the all threads need to be inserted into the carbon fiber tubes? I was thinking about 1/2", would this be enough? . I am also JB welding 3/8" long aluminum sleeves on each end of the tubes. The longest rods will be 4 to 5" of carbon fiber.

Is JB weld the best glue for this operation or is there something better?

They will be installed on a 60" Edge 540 with a Saito 91.

Thanks
Dowayne

I'm really not sure if 1/2" is far enough in for my liking. I guess I would suggest at least 3/4" to 1".

I use the smaller diameter (1/8")pushrods available at www.darrolcady.com

I'm starting to use these for just about all of my pushrods now. At his prices, you can afford to do this. A 2/56 rod is a slip fit in the 1/8" pushrods. He sells a glue called Black Flash that works great on Carbon Fiber. Its a medium CA type glue with very tiny pieces of Rubber inside. Works Excellent for these types of pushrods. I've also used 20 minute epoxy, which works fine. I've heard alot of people do use the JB Weld so I'm sure you will be fine. Be sure to roughen the metal rod with sand paper and then clean with alcohol or acetone for best adhesion.

The sleeves you mention are a good idea. I have done them with and without sleeves, and not had a problem, but I still think it is a good idea.

Dowayne,
I think 1/2" insertion would be enough. Can't answer you question about JB weld with fiber rods though.

Just as a side note, when I worked for Hughes Aircraft some years ago, we did an analysis to see how many threads engagement were required to equal the shear strength of a bolt or screw. The answer might surprise you - only three! In other words, if you have less than three threads engagement, you can strip the threads under stress. But with three or more, the bolt will shear first. Of course, this is assuming that the material you are threading into is the same as the bolt or stronger, which wouldn't be the case with JB weld, but 1/2 engagement for a 4-40 thread is 20 threads. That should be plenty as long as you get a good bond to the fiber rod.

Russ.

I am using the Darrol Cady rods on mt 29% Edge and they are great. I use 1/2 of thread in the rods and it is no problem. I have been using the rubberized CA too (FlashBlack) and it is great. It has a lot of other uses because it resists vibration and is easier to sand than regular CA....though not easy.

Bob

I've been using Beman brand CF arrow shafts for pushrods for some time now on both small .40 size to gas powered aircraft. I turn a dowel down to a slip fit within the shaft, glueing about 3/4" of the dowel into the shaft. I use medium super glue or epoxy - doesn't seem to matter as long as the surface is clean/dust free (big hint). I suppose it wouldn't hurt to roughen the inside walls up a little with fine sandpaper to improve adhesion, but I haven't bothered and it's worked OK. I drill the dowels ends to accept a length of 4-40 or 2-56 fully threaded rod which I glue in using medium CA. I usually cut the threaded rod end to about 1 or 1 1/4" length. It's that simple, and works great.