Pull Test Update -- 6/5/05

I made up another pushrod -- 2" of pultruded 1/8" OD CF tube, 3/16" long brass ferrels, 1/16" wire pins. The wire was well roughed up and inserted 3/4". Everything was cleaned with acetone and one end was glued with Elmer's Probond (polyurethane that activates with water); I used JB Weld on the other end. The JB weld had set up about 43 hours; the ProBond has about 30 hours.

I could not manually pull the pins out. I wanted to have some sense of how much weight it would withstand, so I suspended a pair of vice-grips from a treelimb, snapped a second pair on the other end of the pushrod and stood on a scale. I weigh 210 -- so I pulled on the pushrod until the scale read 100 pounds -- I'm assuming that the rod was carrying about 110 pounds of pull. I figured if something broke, I could have a face full of vice-grip so I stopped. I loaded the rod to 110 pounds twice.

Results:

30 min. epoxy failed at 80 pounds of push.
ProBond loaded to 130 pounds of push without failure (a check showed no plug of ProBond behind the wire -- good point by Bipe)

JB Weld and ProBond did not fail at 110 pounds of pull.

So, with a little care in cleaning and surface prep, either JB Weld or ProBond joints will give adhesion strength greater than the structural strength of most of our planes. I'm very impressed with the performance of ProBond -- one part and easy cleanup. One note of caution: Choose your carbon fiber tubing with an ID close to the wire size to avoid too much of an adhesive bridge.