Friday, May 24, 2013

Carbon Cable Guides

I started working on some carbon cable guides for the latest frame.  After a few tests of two quick molds I manged to get an acceptable guide blank for testing.  Here is the progression from mold one, under compacted to mold 2 fully compacted and cured solid carbon composite.  These were made out of woven pre-preg and baked in the oven.
I ground, milled and sanded one into shape and test bonded it to a frame tube with DP-420.  I'll do some load testing to failure before applying them to the frame.
Another view.
The joint epoxy coating and sanding is almost complete as well.


Crash said...

Those look pretty but unfortunately they aren't going to be safe. What you have there, in engineering terms, is called an "unsupported single-lap joint". What that means is high peel stress and certain failure. UD can't take peel/cleavage stress and it's skin will fail before the adhesive bond. To redistribute the stress, you need to increase the bond surface area and decrease the cable distance from the tube.

Crash said...

Here's how I make my guides now:
Guide plug
Cable Guide

Glen J said...

I tested the guide pictured and the glue bond failed at over 70lbs of cable pull, not the UD of the tube. They are not being used for brakes.

Crash said...

Very interesting that the bond failed first. Cohesive or adhesive mode failure? DP420 has a higher bond strength than your laminate resin. It shouldn't have failed.