[TheForge] A different needle question

[Peter Fels & Phoebe Palmer]

Bruce; It's probably a reflectivity/emission problem.
I suspect Mr Lang's simple approach is the most practical.
Take the plate of steel, grind the face clean,
heat to temper color and plop the needle on the plate
away from the fire. Then set it aside to cool.
Also, why draw the temper so far? 
My inclination would be to go for a dark straw yellow 
unless the alloy or carbon content are pretty extreme.
The main difficulty is the tiny cross section of a needle point.
It's going to instantly become the same temperature as the atmosphere around it.
Consequently, overheating , both during hardening as well as tempering,
presents a formidable challenge.

On Oct 22, 2013, at 3:44 PM, Bruce . wrote:

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
>> ______________________________________________________________
>> TheForge mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/theforge
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:TheForge at mailman.qth.net
>> 
>> TheForge mail list group photo site is
>> http://www.shutterfly.com
>> Login: blacksmithblacksmith at hotmail.com
>> Password: anvil
>> 
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
> ______________________________________________________________
> TheForge mailing list
> Home: http://mailman.qth.net/mailman/listinfo/theforge
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:TheForge at mailman.qth.net
> 
> TheForge mail list group photo site is
> http://www.shutterfly.com
> Login: blacksmithblacksmith at hotmail.com
> Password: anvil
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
______________________________________________________________
TheForge mailing list
Home: http://mailman.qth.net/mailman/listinfo/theforge
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:TheForge at mailman.qth.net

TheForge mail list group photo site is
http://www.shutterfly.com
Login: blacksmithblacksmith at hotmail.com
Password: anvil

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html