Pushrod testing

I've been using carbon fiber rod for pushrods lately. For the 1/2A stuff, I use .070 solid rod epoxied to brass ferrels. On short runs, they work without support, but need a midlength guide to prevent bowing on longer runs. There is essentially zero stretch. However, the rod is too light to use on .15 sized and up.

1/8" OD pultruded tubing seems to be about right with sufficient stiffness for larger models. However, I wasn't sure how well I could get the 1/16" wire to adhere in the ends or what might be the best adhesive. So the experiment ---

Pultruded CF Tubing: Purchased from Kitebuilder.com
ID: .068
OD: .125
Grams: 10.13
Length: 48"
Price: 3.33

I prepped the CF tubing with acetone wiping the outside and using an acetone soaked balse stick to swab the inside. I roughed up 1/16" wire with 80 grit and wiped with acetone. Brass ferrels about 3/16" long were cut and prepped. I made up two test rods, one using Elmers ProBond polyurethane and the second with 30 minute Hobby Poxy II. The wire was inserted 3/4" in both and both cured 24 hours.

I drilled a 1/8" hole in a 2x2 deep enough so that about 1/4" of tubing below the ferrel was exposed -- I wanted to see how well the wire was retained and not break the rod off. I set the 2x2 on a scale and pushed down on the wire end with a steel plate. At about 80 pounds, the epoxied wire was slowly pushed into the rod -- it was not an immediate breakdown, just slid in. I was able to load the ProBond up to 130 pounds, but it held.

Frankly, I was surprised that the ProBond beat the epoxy and that it held up at 130 pounds (tested it twice at 120 and once at 130). Bottom line is that either adhesive will produce a bond strength greater than any of the other parts on the model can withstand.