Date: Wed, 03 May 2006 17:58:59 -0700
From: R3~ <radius11-AT-covad.net>
To: puptcrit-AT-lists.driftline.org
Subject: Re: [Puptcrit] OT-Old Fashionned tool Advice?


Unfortunately it is quite a bit different that McDonalds, both due to 
the possibility of shattering metal, which I have seen several times and 
heard of, reliably, dozens of times, and the toxins that are released 
when the additives in motor oil burn.  'Normal' motor oil is bad enough, 
and I have seen people swoon from the effects of using it as a quenching 
agent, though the newer synthetics are even worse for what they contain 
and have the potential to release.  I'm not saying that you're going to 
go up in a mushroom cloud, but safety is the first rule, and why take 
the chance?  Just because you might get the results you want, for 
however many years, doesn't mean the process is beyond examination and 
revision.

There is also the issue of attaining the critical temperature for this 
process to work correctly- not to high, not to low or you can get no, to 
disastrous effects.  Some people learn the heated steel 
coloring/temperature scale for a particular steel faster than others, 
some never learn, and wing it, sometimes resulting in what they wanted, 
but often times not.  All of the effects of correct, or incorrect 
quenching are not evident immediately, as they relate to the grain 
structure and stresses within the metal.

Ray~

Kismet wrote:

>As Ray pointed out its not a process to be be undertaken lightly and 
>probable not worth it for a fine file...all my bastards are done for stone 
>work but its funny how familiarity breeds contempt, having being taught the 
>process some cough cough splutter cough years ago I resort to it 
>occasionally for a finish on a sculpture or a part for one of my 
>bus/motorcycle/vintage car/sculpture tool collection...never needed it for a 
>puppet though.....and have never encountered a suggestion that it may be 
>unsafe... beyond the fact that we are dealing with very hot metals
>The processes are the same.... Case hardening, in the case of mild (low 
>carbon) steel involves heating a metal to a temperature that allows 
>additional carbon to combine with the iron molecules to form a harder steel 
>on the outer mico millimetres, forming a case.(High carbon steels only 
>require heating and then quick steady cooling)  there are proprietory 
>"glazes" that can be applied at a lower temperature and then heating to a 
>higher temperature to allow the carbon to impregnate the steel, in this case 
>the item is plunged into cool water WITH oil floating on top to reduce the 
>risk of thermal shock. In my example the  high carbon content liquid, motor 
>oil, impregnates the steel with carbon as it cools. The problem with rapid 
>cooling, such as using water, is the crystalising effect on the steel 
>molecules wich CAN create a thermal shock, oil cools a lot slower (in 
>relative terms) and creates stronger molecular bonds.....I think Im 
>remembering my physics right, been a long time. Apart from an occasional 
>flare from an overheated piece Ive never heard of any one encountering a 
>problem and its certainly no more dangerous than what a deep fryer 
>encounters at McDonalds every day.
>These days a lot of case hardening is actually replaced by using a MIG 
>welder to create a basket around an item, something to mention at a 
>party...or you could mention that early case hardening was done by cramming 
>the mild steel item into a sealed tin with cow bones and hair then heating 
>it to glowing red hot for a few hours. The smouldering bones and hair, 
>without much oxygen, created a carbon gas that impregnated the steel....... 
>Obviously I go to some great parties!
>
>D.
>Dont know much about Stainless except that you cant cut it very well with an 
>Oxy or a grinder which means its not much use to me. 
>
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