[TheForge] A different needle question

[David E. Smucker]

Best way to color temper something of this nature is to place a steel plate on your stove (gas works best) and then place the items to be temper on the plate.  This lets you seen the color without looking at the flame and lets you stop the temper action by dumping the contents of the plate in to a pan of water.  Not sure why you are having issues polishing the needle, just use a buffing wheel.  The use of the plate to heat treat gives you control over the rate of heating (slows it down).  Have used this to temper small parts, it is an old machine shop practice.

Dave Smucker
Brasstown, NC

-----Original Message-----
From: theforge-bounces at mailman.qth.net [mailto:theforge-bounces at mailman.qth.net] On Behalf Of Bruce .
Sent: Monday, October 21, 2013 6:24 PM
To: Blacksmithing List Sponsored by ABANA
Subject: [TheForge] A different needle question

​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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