PSN-L Email List Message

Subject: Re: Teflon tubing for paper recording system...
From: "Charles R. Patton" charles.r.patton@........
Date: Thu, 04 Aug 2011 09:24:02 -0700

As I have never used an ink pen system, this may be totally off base, 

My understanding of most pen chart systems is that the ink flows under 
capillary tension down the tubing (** this note excludes pressure feed 
ink systems **).  If this is true, then it would seem to me that Teflon 
would be one of the worse tubings to use as it basically doesn't wet.  
This would then block the flow of ink in the tubing.  The chart systems 
I have seen have always used a steel tube for the final "pen".  No 
problem there as steel will wet just fine.  The tubing I thought I saw 
was either rubber (short life) or PVC.  PVC is extremely easy to find.  
Pretty much any hook-up wire is using PVC insulation except for 
aerospace and military wire insulated with exotic materials such as 
Teflon, Kynar, Polyolefin, etc.  Strip the insulation off of  #14 house 
wire for tubing with an ID of .0663".  For something on the small end, 
use  solid CAT5 or similar (PC LAN cables or the inside-of-the-house 
phone wiring.)  A piece I just measured is 0.0193" which puts it at 
about #24 gauge.  So depending on your selection of wire, you very 
likely have a source close to hand.  Cheaper than ordering out!

For needles two sources I can think of are:
   1) Your friendly doctor.  I think that it may be illegal to own a 
needle in the United States, so you may not be able to go this route.
  2)  A lot of epoxy applications use a syringe to apply.  Usually the 
tip is a plastic part that screws on (half-turn).  But metal needles are 
also available.  They just aren't sharpened like an injection needle.  
Instead they are cut off square.  This would be nice because it also 
gives you method of removing the needle and refilling your "syringe ink 
cartridge" with the simple pull of the plunger.  So check with your 
local plastics/epoxy supply company.

Charles R. Patton

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