[TheForge] A different needle question

[Bruce .]

Good idea.  I tried it (using a griddle as the thermal mass).  Didn't
work.  I suspect poor heat transfer.

Bruce
NJ


On Tue, Oct 22, 2013 at 2:20 PM, Paul N <crosspein at sbcglobal.net> wrote:

> How about getting one of those cheap H-F non contact thermometers
> Then heat up something more massive to the desired temp and place the
> needles on there for 15 minutes or so?
>
>
> **paul
>
> Sent from my little tiny screen and keyboard. Any autocorrect errors are
> solely for your entertainment.
>
> > On Oct 21, 2013, at 5:24 PM, "Bruce ." <freemab222 at gmail.com> wrote:
> >
> > ​I am altering the eye shape of a few commercial needles.  They're too
> > brittle to work without normalizing, but onc​
> > ​e normalized, they bend just fine.
> >
> > Now I need them hard again.  Well, dunking in water while at a red heat
> > works for that -- but leaves them more brittle than ever.
> >
> > A tempering operation (to purple or blue, probably) is quite easy on a
> > chisel, but even SEEING the colors on a needle is a challenge.  For one
> > thing, there's no good surface to polish.
> >
> > I've tried a couple methods, all without success -- my toaster over
> doesn't
> > get hot enough, like, maybe 450 F, despite what the dial says.   (520 F =
> > purple, 540 F = blue, 590 F = peacock, according to one reference.)  I
> > tried heating an iron griddle to these temperatures and leaving the
> needle
> > on it for about 5 minutes -- no luck.
> >
> > I considered using a salt or solder bath, but find no appropriate salt
> and
> > that I'd need 80/20 to 85/15 lead/tin solder -- which is not readily
> > available -- to get a liquid bath of the right temperature.
> >
> > I'm considering a sand bath or a furnace, using a thermocouple to monitor
> > temperature, but as you can see, this is getting increasingly complicated
> > for what should be a rather simple task.
> >
> > Hence, I'm soliciting suggestions how to temper a needle.  Any notions?
> >
> > Bruce
> > NJ
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