Metal finishing Q&As since 1989

-----

Aluminum finishing and bushing material

2003

I would like information as to what surface treatment for Aluminum and bushing material would work best for a particular project I am currently working on. I am designing a lightweight suspension system for a bicycle. The suspension will primarily consist of two Aluminum tubes (7075 material) telescoping one within the other separated by Teflon bushings (proposed material) and lubricated with light grease. The system will be constructed with close tolerances, no more than .0005‡ between the bushing and the tube wall. Bushing thickness will be approximately .075‡. The system will be subjected to a static moment load of 240 ft-lbs. and brief moment loads of at least 3 time that much as well as axial loads. The axial loads will cause the tubes to telescope and they must do so with a minimum of friction.

Thank you for your time and attention to this matter.

Michael Snyder
Design Engineer - Ramona, California, USA

This is not my area of expertise, so I could be totally wrong.First, 5 tenths is a press fit, I somewhat doubt if you will get the movement that you appear to want. Second, teflon tends to move or give way under pressure (long term) so I would expect it to deform sooner than you expect. Look at ultra high density polyethylene which is also easier to machine accurately and is nearly the same friction as teflon. For the inner tube (rod) I would look at chrome plate, diamond ground to precise size (many machine shops do a bad job of grinding-It has to be done slowly, especially on aluminum and with the CORRECT WHEEL) An alternative is electroless nickel which possibly would not have to be ground after plate if the starting size was correct (and uniform) and you have a good EN plater.

James Watts
- Navarre, Florida
2003