Talk Composites - The Forum for Advanced Composites

Carbon Fibre tube or rod for clock pendulum

http://www.talkcomposites.com/Topic25196.aspx

By Mikeso51 - 2/14/2018 9:57:45 AM

I want to use a 6 mm carbon fibre rod or tube as the pendulum rod in a precision clock that I am making. The pendulum bob weight is 5 pounds.
The rod needs to be rigid, have a very low temperature coefficient of expansion, and must be dimensionally very stable.
Questions:
Is there anything to choose between rod and tube?
Is a pultruded item better than wrapped in this application?
Should I be looking for a product that uses epoxy rather than polyester resin?
Would a gel coated item be better from the point of view of water absorption?

Any advice would be greatly appreciated

Mike
By Mikeso51 - 2/15/2018 12:45:40 PM

 
Warren (Staff) - 2/14/2018 3:57:19 PM
There is a massive difference between a rod and tube of similar size.  The rod will be much stiffer due to the volume being solid.   Pultruded items have their fibres orientated only down their length.  The roll wrapped tubes have fibres both down the length and around the tube for crush strength.

Most good quality tubes and rods are epoxy anyway.  You may find some vinylester  ones around  as well. 

You will be unlikely to find an off the shelf tube or rod with a specific gelcoat applied.  Tubes such as the woven finish tubes can be lacquered for a high gloss finish which will also give you a good surface seal if you are worried about moisture absorption.

Thanks Warren.  Very useful.