[TR] Taps & Dies

[Randall]

>  I have used a lot of hardware-store taps over the 
> years and most of them are rubbish sutible only for cleaning 
> up existing threads in soft metal. 

Which presumably is exactly what we're talking about here.  The very few
hardened fasteners on a TR should be replaced if the threads are damaged,
IMO.  And while the need to fabricate parts during a TR6 restoration does
sometimes arise, hopefully it's not often (since the hand-fabricated part
will not be a match for the "correct" part).

As I understand it, high speed steel is appropriate for situations where the
cutting edge potentially gets hot enough to soften carbon steel; which
generally means a power tool is involved.  Otherwise, ordinary carbon steel
actually holds an edge better.  Hand-tapping would seem to usually fall in
the second category ... although I must admit, I finally wore out a 30 year
old carbon steel die a few days ago, cutting threads on drill rod with it.
But if it didn't have a couple of broken teeth, I'd sharpen it and go on.

> Just don't use it in cast iron. :-)

I'll bite, what's wrong with using cutting oil in cast iron ?  

I very rarely cut new threads in cast iron anyway; and generally don't
bother with it when I'm just chasing old threads; but the few times I've cut
new threads in cast iron, the cutting oil seemed to help.

Randall 
(Tedious but unavoidable disclaimer follows) 






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