Spot annealing

Djl338

Djl338

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Hi all
I need to add an extension to a firing pin, the back of the pin is 7mm and need to put a 70mm 9/64”) drill rod silver soldered on the end. Tried drilling with a 9/64” carbide bit, and got nowhere. I’ve heard about spot annealing. the video I watched used a small torch, that doesn’t seem very “spot”
Any tips?
 
I have not heard of the term, but it likely involves a large piece of tool steel so the block is only locally heated to cherry, then allowed to slowly cool.

Is there a problem annealing then heat treating the entire piece? It's really hard to get a portion of a small part red hot without conduction heating the entire part through.

Bruce
 
I can't say if it'll work in your application, but I remember the following method from some "old timey" shop book.

The author needed to drill a number of holes thru a hardened part.
For "spot annealing" he put a regular plain shank nail into his drill press chuck (point up).
Then clipped off the head (...and may have ran it against a flat file on the table to square the end).
That steel rod was then turned at high-speed against the work piece exactly where he needed holes.
The friction caused both the nail and the spot on the part to turn red hot.
It was then cooled slowly.
He then successfully drilled the holes.

I have NOT used the technique myself, but it obviously made an impression on me 'cause I have remembered it for years.

I think the book was one of the three in the collection; Alexander Weygers The Complete Modern Blacksmith.
https://www.amazon.com/Complete-Mod...rn+blacksmith&qid=1557852494&s=gateway&sr=8-1

It is a great set of books; highly recommended.

Please let us know what works for you.

-brino
 
Thanks, that’s pretty cool!, I never heard of “spot annealing” until I tried looking up methods to drill into “ kryptonite”. I was trying to avoid heating the entire part so I didn’t mess-up the part that needs to be hardened, maybe I’m wrong?
I actually have that book, maybe I need to actually read it it more detail, thanks for the tip, I’ll see if it works
David
 
What firearm is firing pin out of??
 
brino said:
For "spot annealing" he put a regular plain shank nail into his drill press chuck (point up).
Then clipped off the head (...and may have ran it against a flat file on the table to square the end).
That steel rod was then turned at high-speed against the work piece exactly where he needed holes.
The friction caused both the nail and the spot on the part to turn red hot.
Click to expand...

This method is also used to put holes into hard flat springs, such as used for clock mainsprings.

-frank
 
Glad it worked out for you.
Another thing that has worked for me when I had to drill and tap scope mounts in a 1943 Swedish Mauser that had a "Kryptonite" receiver was to use a solid carbide 3 flute drill to make the hole. The resultant hole was still way to hard for any tap I could find. So I put the shank of one of the cobalt drill bits, that I burned the tip off of trying to make the hole, into the hole and heated the the drill bit to red hot allowing the heat to conduct into the surface of the hole and slowly remove the heat from the drill bit to cause the hole to cool slowly and it tapped just fine after that.

I will add the spin heating to my memory bank for future though.
 
Flyinfool said:
Glad it worked out for you.
Another thing that has worked for me when I had to drill and tap scope mounts in a 1943 Swedish Mauser that had a "Kryptonite" receiver was to use a solid carbide 3 flute drill to make the hole. The resultant hole was still way to hard for any tap I could find. So I put the shank of one of the cobalt drill bits, that I burned the tip off of trying to make the hole, into the hole and heated the the drill bit to red hot allowing the heat to conduct into the surface of the hole and slowly remove the heat from the drill bit to cause the hole to cool slowly and it tapped just fine after that.

I will add the spin heating to my memory bank for future though.
Click to expand...
That’s a great tip, I’ve run in some hardened things that I shyed away from tapping. Yes, the $16.00 carbide bit that I burned up, was turned around and initially used to try it to anneal, it didn’t seem to heat up the area? then I switched to the nail and that heated up pretty quickly. I actually used a hss drill bit to make the hole, it was pretty amazing
 
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