Paul Stubbs on sat 6 oct 07
Hello Paul we have spoken in the past on the hd pug mill My solution to this
one was to use a pieces of old metal files cut with an abrasive disc welded
on and cooled instantly in water. They seem to stand the test of time and
have only been renewed from time to time. The machine is perhaps some 35
years old now, the valve is not the best part of the design and as you
probably know was superseded by a valve less variant later. this is
explained in his book I can let you have a copy of the relevant bits if you
need them
(I believe the Venco machines use this element)
Keep pugging
Paul Stubbs (UK)
Date: Fri, 5 Oct 2007 13:32:29 -0400
From: Paul Borian
Subject: hardening tool steel for Harry Davis pugmill cams
I have always wondered why the tool-steel cams on the breather valve for
my Davis style pugmill wear out faster than they should - Vince told me
that he was getting like 7 years out of his cams where as I have
replaced mine at least once per year, sometimes twice, even though I
followed the directions for quenching them after welding on his plans. I
just got off the phone with someone from Speedy Metals in WI who was
amazed at how clueless I was about tool steels when I was asking about
pricing and various grades - one of these guys who kind of laughs at you
but also helps answer your questions at the same time - and by the end
of the conversation I realized I have been doing it all wrong. He said
for A-2 tool steel (the most common grade) you need to heat it up with a
torch to around 1750 F and then let it air cool instead of quenching it
because it was designed to be an air-hardened steel. I guess Vince was
using a totally different type of tool steel that worked best with
water-quenching.=20
For anyone out there familiar with tool steels, does this sound like the
best way to go for the application or should I consider a different type
of tool steel that was designed to be water-hardened? I am sure they guy
I spoke with knew what he was talking about, but I would still like to
hear it from someone else just to be sure.
Thanks,
Paul
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