Jump to content
Military Firearm Restoration Corner

Spot Annealing


Limpid Lizard

Recommended Posts

I am trying to drill the Siamese Mauser I am making into a 257 Ackley Krag Improved. It is harder than the hubs of hell. My usual practice on DHT Springfields is to polish a small spot and heat it until it just turns blue. I do this 3 times and it spot anneals the small area.

 

On the Siamese, I find the hardness to be completely throught the front reciever ring. I packed it in heat stop paste and did the above 6 times. I could drill partially through, and then had to heat the hole a couple of times to finish. I tried to go with 6X48, but I could see the tap flex as I tried to tap, so I drilled the hole out for a #8 screw. The larger tap is not flexing as much, but I cannot tap beyond the tapered part of the tap. That is, as soon as I get to the straight shank, I can see it flex.

 

I tried heating the #6 hole before tapping hoping to anneal the sides. I failed to anneal it sufficiently to tap and moved up to the #8. The only other receiver I have worked on that was this hard clean through was a 6.5 Jap. Someone before me had tried to drill it for a receiver sight and gotten the holes canted. I drilled new next to them and welded up the others. Since I was drilling on the bridge and knew I was also going to be welding, I was a lot more judicious with the heat. I am leary of heating the Siamese receiver ring to that extent.

 

Do any of you have a good method of spot annealing this receiver? LL

Link to comment
Share on other sites

on the harder receivers i use a titanium coated bit ( the gold colored ones) one size smaller than needed then ream with correct size bit then tap with the higher quality taps i had some black taps that where P.O.S. and broke one after that i spent a little more on them with the titanium bits i havent had any problems drilling thru as far as anealing i have never had much luck with it im sure some of the other guys will chime in with suggestions but you may end up having to anneal and reheat treat the receiver to a known hardness it sounds like that one is harder than woodpecker lips :P

 

james

Link to comment
Share on other sites

I have one hole drilled and tapped. It took a bit of headscratching to figure out how to do it, but I think I have it under control. I ordered a fist full of new taps from Brownells, and this project is on hold until they arrive. I want a new tap for each hole.

 

I am wondering if the lack of substansive response to this question is because I have B.O., or if the knowledge base here is smaller than I imagined. I have been a serious hunter a good portion of my life. When asked to describe what a hunter is, I have always answered that it was a person with the ability to take various game animals under various conditions. The person with 40 whitetails to his credit was not necessarily a good hunter. He was good at one thing.

 

My understanding of gunsmiths is the same. One should be versed in all aspects of gunsmithing, not just in one narrow niche if one is to be considered a gunsmith. I do not consider myself a gunsmith, as my experience is limited by hobby level involvement. I was lambasted pretty harshly for mentioning that under certain conditions I preferred forged bolts. The person lambasting me specifically mentioned the amount of effort some here put in learning the trade. At this point, I ponder whether we have any well rounded gunsmiths aboard, whether we have niche artists, or whether I was not given help from the supposedly talented due to having ruffled a few feathers. Either way, If you need the answer, I will be glad to share. LL

Link to comment
Share on other sites

I learned a long time ago not to chime in on something that I don't have personal experience with. I never drilled a Siamese, nor have I had to wrestle with one of those other glass-hard actions.

 

I have always used and advocated Carbon steel bits and taps for Mauser work, primarily because when you break one -- and you WILL break one -- you can generally fracture it and pick out the bits. I think that if I were given your circumstances, I would try a carbide drill and a HSS tap. That is just what I would try, however, and it comes not from experience but from intuition.

 

Do use a good quality commercial tapping fluid like "Rapid Tap."

 

Good luck!

 

Clemson

Link to comment
Share on other sites

Clemson is right about using carbide bits and taps. I ran into a very hard receiver on a late war Nazi Mauser. I broke a drill bit or two on it. I then ordered some drill bits from MSC for drilling high Rockwell numbered steel. They work very well. That's all I use now. If I break one of those, and I have, it is from carelessnes. I will see if I can find the number for the bit later when I am at home.

 

vlad

Link to comment
Share on other sites

I've tapped some very hard receivers and never needed to anneal anything. I know how to spot anneal but never had too. Instead, I use a GOOD drill bit and new high carbon tap for each hole. The key is in using a spring loaded center to keep the tap straight. Even if you use a B-Square or Forster fixture you need a center to hold the tap straight.

 

It's good to know that I'm considered a hack now that I've confessed to not having spot annealed. I rust blue but don't caustic blue. I suppose that makes me a beginner hack. Good to know one's place in the scheme of things.

 

You know, often we don't have time to read every post. I'm sorry I took the time to read this one.

Link to comment
Share on other sites

I am going to go out on a limb here and offer an opinion on something that I didn't actually witness. It SOUNDS to me like the areas that were spot annealed were allowed to cool too rapidly. After being heated they need to cool very, very slowly. Just removing the heat source and allowing it to sit may be allowing the area to remain in a hardened state. The cross sections where the holes are located are thin. The few times that I have had to do this I just used the torch and kept the heat on and gradually backed it off. This can be tricky if you are not careful and have a good bit of experience with a torch. Something else that may work a little easier and more controlled is to fill a metal coffee can with dry sand, heat it in the oven to about 350 deg. or so and get the sand thoroughly heated. Heat your receiver spots and immediately bury your receiver in the sand. Let it cool until the sand is cool to the touch. Having said this I will also say that I have never even seen a Siamese mauser action. I have had to spot anneal a few holes in other mauser actions and I think either method will work well for you.

 

I also have a drill that I bought to drill out a broken high speed steel, 6-48, tap. It is tiny. It cost over $20. I looks like it would break if you dropped it on the floor. It drilled through the tap like it was made of butter. I was amazed to say the least. I bought it from Travers Tool Co. but that is all I can remember about it. Just be careful, earlier someone posted that he used only carbon steel taps for easier removal in case it breaks. Someone else suggested using a carbide tap. These are extreme opposites in the hardness and brittleness areas. When you break that carbide tap off in the receiver thing are going downhill fast. There are only a few ways to get it out and you ain't gonna like none of them. Be careful and good luck!

Link to comment
Share on other sites

Thank you for the replies. They stimulated my thoughts. The first hole I tried was the one closest to the receiver lug. It was the one I wrote about. I left it with 3 full threads the other day and decided to think this through and approach the problem fresh. While thinking about this, it dawned on me that the handguard ring was easy to remove, the ribs on the sides were easy to remove and the charger hump was easy to remove. This receiver could not be a hardenable alloy. It had to be carburized as are other Mausers.

 

I have a small Jacobs chuck mounted on a straight 1/2" shaft. I use this to tap with by leaving it a slip fit in a R* collet in the Bridgeport. I find this eliminates side movement and gives me a better feel for the tap than if I was using a handle that increased leverage.

 

To anneal the hole enough for threads, I turned a 5/8" piece of CRS to fit the #8 hole. I left about 3/4" full diameter above the hole. Using the torch, I heated this until it was red through out and had a good puddle on top. When it cooled to gray again, I reheated it. I did this 5 times. This allowed me to cut the 3 full threads, and knowing this was going to work, I stopped rather than continue while frustrated.

 

The remaining threads in this hole were a little more difficult than normal to tap, but I noticed no flexing of the tap as I applied torque. I just took it slow and easy, using a new tap every couple of revolutions of the spindle. The remainder of the holes drilled and tapped normally. The case could be felt on top and when breaking through the bottom. If I was to guess, the lug recess was probably packed during carburization to provide carbon for case hardening the lug, and the carbon probably was absorbed through out the lug recess material. As I said, that is just a guess. I'm probably full of caca.

 

If you have a steady hand, one way to remove a broken tap is with an O/A torch. Using a fine tip, heat the top of the broken tap until it starts to puddle. If you increase the oxygen just slightly at this point, the tap will blow out. The hole will be okay. It only takes a moment to heat the tap, and if you pack the surrounding area in heat stop paste you will not annean the surrounding area. This is the poor man's EDM.

 

 

Link to comment
Share on other sites

×
×
  • Create New...