Re: ATM where do u get teflon strips

[mdholm@telerama.com]

Although the molecular weights of Teflon (polytetrafluoroethylene, PTFE) are 
typically quite high, the abbreviation UHMW (ultra high molecular weight) is 
almost always applied to a type of polyethylene.  They look a lot the same, but 
friction performance is different.  UHMW is tougher, cheaper and more abrasion 
resistant, but has higher friction.  PTFE is considerably more heat resistant, 
fire resistant, chemical resistant, and has lower friction.

A very well researched and written article in either the most recent, or next 
most recent S&T Telescope Techniques section presents careful friction 
measurements of a variety of materials.  Conclusion: We should be using a 
cousin of Teflon known as PFA  (stands for perfluoroalkoxy).  The DuPont 
version is tradenamed Teflon PFA.

Absolute friction of PFA against Ebony Star or similar is a bit higher than 
PTFE Teflon, but the curve of friction vs. sliding speed is much closer to the 
ideal that every Dobsonian builder wants.

Read the article!

PFA is a bit rarer than PTFE, but DuPont has been making the stuff for 20 years 
or more.  By now, the patent is long run out.  There may be other 
manufacturers than DuPont.  Solvay is one possibility, they make other 
fluoropolymers.

DuPont makes the resin.  Other companies may make it into sheets, so it may 
not carry the DuPont brand name, but still be DuPont's resin.  In US, Canada 
and Western Europe it shouldn't be too awfully hard to find.

-- 
Mark Holm
mdholm@telerama.com