Re: ATM where do u get teflon strips

["Jim Miller" <jim@jtmiller.com>]

pfa appears to be pretty pricey: http://www.sdplastics.com/pfa.html

tried mcmaster and they didn't have it in sheets at all.

any other places?

jtm
----- Original Message ----- 
From: <mdholm@telerama.com>
To: <atm@shore.net>
Sent: Sunday, October 19, 2003 5:35 PM
Subject: Re: ATM where do u get teflon strips



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