[GreenKeys] platen refurbishing FYI

[Richard Knoppow]

     There is an explanation of the Shore Durometer hardness 
scale at:

http://www.smooth-on.com/-Documents-Duromet/c0_1351_1370/index.html

     It turns out there are three scales in use which 
overlap.  The hardness specified on one is not the same as 
on the others.  Shore A00 is for the softest materials, 
Shore A for medium-hard materials, and Shore D for the 
hardest materials.  One can have the same numbers on two 
scales for quite different hardnesses.  Shore D 100 is very 
hard but Shore A00 100 might be suitable for a typewriter or 
Teletype platen.
     BTW, I have an IBM Selectric II, the platen is fairly 
hard, perhaps slightly harder than on a couple of portable 
manuals I have testing with a fingernail.  Its about the 
same as on an Olympia office machine.

--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com


----- Original Message ----- 
From: <Til128 at aol.com>
To: <greenkeys at mailman.qth.net>
Sent: Saturday, March 09, 2013 4:53 PM
Subject: Re: [GreenKeys] platen refurbishing FYI


> Hello all -
>
> I'm having the platen on my M15 re-covered.  It was  rock 
> hard, and the
> type bars were perforating the paper, even when I backed 
> the  typing force
> adjustment as much as possible.  The guy doing the 
> restoration  says that the
> platen currently measures a 100 Shore-A, which is the same 
> as  "modern" (lol)
> Selectric typewriters.  He says older typewriters used a 
> 90  Shore-A
> material, but claims that the softer material could allow 
> perforation of  the paper
> and ribbon, which is exactly the problem I'm having now...
>
> Does anyone have an opinion on this?
>
> ----------------------------------------------------------------------
>
> Some measurements for Shore durometer "A"
>
> Rubber band 25 A
> Door seal 55 A
> Automotive tire tread 70 A
> Soft  wheels of rollerskates and skateboard 78 A
> Hydraulic O-ring 70-90 A
> Hard  wheels of rollerskates and skateboard 98 A
> Ebonite Rubber 100 A
>
> TT
>


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