Surfer Dude

I have been trying to tap a carbon fiber rod for a 4-40 with no luck. If anyone can please tell me how to tap the Carbon fiber rod properly? I would really appreciate any help.

Chris

davidfee

I take it you're threading the carbon rod to screw on a clevis or something? Carbon rods will never tap well. The structure is like wood, with fibers running along the length. The material will tend to shatter and crumble rather than cut like metal. However, it can be done. You need a sharp die to cut the threads. Don't use oil. You should also epoxy the clevis on once you have the rod threaded.

good luck,
David

CurtD

My Feedback: (1)

The 5/32" carbon tube can be tapped successfully if you first slide the carbon tube inside a 1" piece of 5/32" ID aluminum tube and slow-CA it. The aluminum tube prevents the carbon tube from splitting. Use a good-quality SHARP tap, no oil, and go slowly.

It's not really necessary to tap it, though, to get a good, solid joint between a 4-40 clevis rod and the carbon tube. The un-threaded portion of a 4-40 Sullivan pushrod is a slip fit inside the 5/32" carbon tube. Simply cut the untreaded portion about 1 to 1.5" long and roughen it with sandpaper. Clean inside the tube with alcohol and a pipe cleaner, and clean the end of the 4-40 rod.

To glue it in you can use J-B Weld or slow CA. Carbon seems to have a high affinity for CA so it actually creates a very strong joint. I've tested to destruction carbon pushrods made this way with CA and the glue joint never failed. It took an incredible amount of force to make the carbon rod break. The 4-40 steel rod will bend or buckle first.