spot annealing?????

[Just1Mor]

So i have a grand made into a bm 59 that started out as a chopped receiver. The guy that put the receiver back together and made the gun was a very tallented tool and die maker and worked in the armery during ww2. the problem is the heat treatment that the rifle underwent was very intence and is very strong. in my quest to mount a scope i need to know if you all could help with how to spot anneal so i dont screw up the entire gun.

[leftiye]

Usually filing a flat through the case hardening will allow you to drill and tap. Anything that reduces the hardness through heating will affect a much larger area than you want to mess up. If the file fails to cut it (pun intended), get some one with a milling machine and a small carbide endmill to cut through the case for you.

[akajun]

When you jig it up in your drill press, use a carbide center drill to "crack the skin" I have even used a dremel stone in the drill press to grind through the skin before.

[stubshaft]

You can use a LARGE soldering iron with a drop of solder at the tip to anneal a small spot on the receiver.

[Bret4207]

Spot annealing works on case hardened type stuff. If he got the whole recv'r hard then a carbide drill is the answer. Of course then the question of the entire heat treatment process done to your gun comes into question.

Good luck.

[John Taylor]

Carbide will get you a hole but how do you tap a receiver if it is hard all the way through?

[Willbird]

Depends how hard. Most through hardened gun steel is around 45 rockwell C isn't it ? The older guys who did a lot of Springfields told me you use a tap to do one gun, then throw it away if you learn from your mistakes ;-). Carbon steel taps are actually harder than an HSS tap. They do make carbide taps too, but they are fragile in small sizes.

One thing that helps with small taps is to make a tap block...for a round reciever it would have a radius on the bottom that matched the receiver, drill and tap a hole through the block, then the tap is guided by the block, and advanced into the work by the block....sort of a mini guided leadscrew tapper :-)...it makes smaller taps a LOT easier to do hand tapping with. You can just hold the block against the part you are tapping, and run the tap in..for a gun you might be able to clamp it on once you get the thread started.....the block allows you to devote 100% of your focus on what the tap is doing while it cuts. I have had to retap some parts where the 4-40 threads were not deep enough before heat treat....just a few more threads needed...that job required a pile of taps, and tons of patience. Those parts were more like 55-60 rockwell M42 HSS.

If you know a machinist that works where they have a RAM EDM threads can be done that way too, in material of any hardness...even carbide....I might make it easier on the poor guy tho and go to the next larger size from 6-48....he has to make and thread a graphite electrode smaller than the tap drill size.

Bill

[Bret4207]

Carbide will get you a hole but how do you tap a receiver if it is hard all the way through?

My question would be if it's hard all the way through is it safe to shoot?!

[theperfessor]

I recall reading an article written by a gunsmith dealing with this issue on a Mauser 98. His solution was to use a VERY small welding tip on an oxyacetylene rig. The pictures showed an orange spot about 1/4" or less right where the hole was to be tapped. Get the heat on it quick in a small area. This was on the receiver ring where the barrel screwed in. I think the rest of the action was wrapped in damp rags.

I have never done this and won't vouch for it but it makes sense metallurgically.

[MtGun44]

+1 on what theperfesser said, including the "I've never done it but it is sound
metallurgically." part.

Bill

[Willbird]

I recall reading an article written by a gunsmith dealing with this issue on a Mauser 98. His solution was to use a VERY small welding tip on an oxyacetylene rig. The pictures showed an orange spot about 1/4" or less right where the hole was to be tapped. Get the heat on it quick in a small area. This was on the receiver ring where the barrel screwed in. I think the rest of the action was wrapped in damp rags.

I have never done this and won't vouch for it but it makes sense metallurgically.

One thing about that is that the area surrounding the heated region can be VERY hard, that happens when you try to arc weld alloy steel without a pre heat, the zone around the weld gets extremely hard and brittle due to the rapid quench from the surrounding metal. It can even break out of the metal right next to the weld.

[Just1Mor]

I recall reading an article written by a gunsmith dealing with this issue on a Mauser 98. His solution was to use a VERY small welding tip on an oxyacetylene rig. The pictures showed an orange spot about 1/4" or less right where the hole was to be tapped. Get the heat on it quick in a small area. This was on the receiver ring where the barrel screwed in. I think the rest of the action was wrapped in damp rags.

I have never done this and won't vouch for it but it makes sense metallurgically.

i have heard of that too. i had also read that you could do it with a sot iron but i dont see how that would help.

and yes this receiver is harder than a rock. I spent hours tring to file a few thou out of the inside of the mad well so the mags went in easier. this guy new what he was doing.

I do have a mill so maybe i just need to get a carbide tiped drill and work at the tap

[Just1Mor]

actually i dont think it would be wise to heat the metal to bright red, anealing steal is a timely process and heating one place up like that would harden it, at least my logic tells me that. Time to pull out the old gunsmith books and see what the say again.

[S.R.Custom]

Carbide will get you a hole but how do you tap a receiver if it is hard all the way through?

This is where your knowledge of metric drills pays off... In the instance of needing to drill & tap a 6-48 screw, I'll carbide drill the prescribed #31 hole. I'll follow that with counterboring the hole a bit with a 3.1mm carbide drill. It's .002" bigger than the #31, yet will still hold the threads of a 6-48 screw. If the steel is really hard, I'll through drill with the 3.1mm bit completely.

Steel that is hard enough to make this necessary won't strip out with the larger hole; the screw will yield first. Use a longer screw if that's possible, and use lots of LocTite.

[Bret4207]

i have heard of that too. i had also read that you could do it with a sot iron but i dont see how that would help.

and yes this receiver is harder than a rock. I spent hours tring to file a few thou out of the inside of the mad well so the mags went in easier. this guy new what he was doing.

I do have a mill so maybe i just need to get a carbide tiped drill and work at the tap

Did he? As a general rule we want our actions tough, not hard. Hard can mean brittle. Most heat treatments for steel involve getting the piece rock hard and then tempering it. I mean no insult to your 'smith, but was this a home HT thing? Was the action tempered or is it just hard? Case hardening is different, a whole nuther game.

[John Taylor]

I just wanted to see what others had to say about tapping hard metal.
I have spot annealed very hard action before. Take a small area up to blue color and let it cool. This is still as hard as a spring but it will drill and tap. The only way to make the metal harder would be to take it to red and quench it, so annealing a small area is not going to make the rest brittle.
Now before I get a bunch of flack about this. I weld the rear bridge on pre war model 70 actions, several a week sometimes, plugging holes. Some of these actions can be very hard, had one split right down the middle while unscrewing the barrel. sounded like a piece of glass when it broke. After welding the rear bridge is heated to a dull red and allowed to cool, other wise I would not be able to machine and roll the mat finish. Even after this treatment the action is very tough in this area. I do not use anything to keep the heat from traveling like some say you have to do. The area at the locking lugs never gets hot enough to hurt it.
Like others have said, if the action is hard all the way through it may not be safe. Look at the early Springfield 03, before 800,000 the hardness was never the same. That's because they did not have a heat treat oven and were going by color before quenching. The actions heated during the day were getting much hotter than the ones at night because the red could be seen at a lower temperature at night.

[Willbird]

Well John, I agree steel gets hard by quenching, but if you only heat PART of an object, the rest of it quenches the heated portion.

Spot annealing may work, but my bet is that it still creates a zone around it that is harder than what it was to begin with. If you have ever tried to weld HSS you maybe have seen this heat affected zone, the weld will break right out of the base metal.

Pre heating the whole part helps avoid the quench from the rest of the part after heating or welding.

Bill

[B R Shooter]

I heard long ago about drilling and tapping hard receivers, to take a small piece of steel, something like a 1/4" and heat it red hot, then just set it on the place you want to drill. Let it cool on it's own. It would draw enough hardness out so you can drill it. Never done it, just passing this along.

[John Taylor]

Well John, I agree steel gets hard by quenching, but if you only heat PART of an object, the rest of it quenches the heated portion.

Spot annealing may work, but my bet is that it still creates a zone around it that is harder than what it was to begin with. If you have ever tried to weld HSS you maybe have seen this heat affected zone, the weld will break right out of the base metal.

Pre heating the whole part helps avoid the quench from the rest of the part after heating or welding.

Bill

The heat put into the spot is only around 700 degrees. To get the steel hard it would need to be heated about double that and then be quenched. Basically what is being done is a small tempering in a localized area. I agree that if it were heated to red it would be cooled very quickly by the surrounding metal and the spot heated would be very hard. This is not what is being done in spot annealing. Welding on high speed steel is not anything close, not even close to the same type of metal. Try annealing a piece of HSS.
I have been working with metal for over 40 years and have discovered a few things along the way. I don't claim to know everything about metal but there are things I work with very often and I have a bit of knowledge about it.

[KCSO]

I use a method show to me by Doc Carlson. I drill with a carbide drill and thne put a rod the diameter of the hole in to the drilled hole. I then heat the rod to red hot and leave it set till it's cool and usually it's then fit to tap.

[nanuk]

all good stuff!

smart people on this forum

[Willbird]

The heat put into the spot is only around 700 degrees. To get the steel hard it would need to be heated about double that and then be quenched. Basically what is being done is a small tempering in a localized area. I agree that if it were heated to red it would be cooled very quickly by the surrounding metal and the spot heated would be very hard. This is not what is being done in spot annealing. Welding on high speed steel is not anything close, not even close to the same type of metal. Try annealing a piece of HSS.
I have been working with metal for over 40 years and have discovered a few things along the way. I don't claim to know everything about metal but there are things I work with very often and I have a bit of knowledge about it.

I love to learn things John, and it does make sense that we are not heating the metal to it's critical point (or should not be anyway) like we would be if we laid a nice bead with a wire welder. So the key thing it would appear is to get enough heat to anneal, but not enough for the metal to reach critical temperature.

And I do see also your point about the HSS, maybe that is exactly why it cannot be welded without pre heat, there IS no annealed zone around the weld. And I HAVE tried to anneal HSS, and do so over and over again if time permits and a thick headed person insists you can damage it to any degree by getting "color" when grinding it. I have silver soldered(high temp) it into things and the HSS still worked as intended afterwards.

[bearcove]

I use a method show to me by Doc Carlson. I drill with a carbide drill and thne put a rod the diameter of the hole in to the drilled hole. I then heat the rod to red hot and leave it set till it's cool and usually it's then fit to tap.

+1 You don't want too much heat.

[MtGun44]

What John Taylor says matches my engineering knowledge of heat treating, quenching and tempering
steel. Combine that with a man that has been doing it for years, and I would not disagree
with his info.

Bill

[Big Dave]

This spot annealing thing is not really annealing in its true meaning. What is actually desired is a further drawing or tempering of the heat treated hardness to a workable level in a small and specific area.

By carefully applying a fairly large drop of solder at the desired location and leaving the tip of the soldering iron in it to maintain a molten state for a minute or so you will heat that area to 600 degrees F or thereabout which will reduce the hardness to a machinable level without risking the over heating and rehardening which is inherent in the torch application someone mentioned above. This will provide a machinable spot with hardness increasing back to its former level in a smooth gradient as you move away from the immediate area and no danger of cracking due to a brittle super hardened boundary as found in improperly done welds.

Big Dave

[leftiye]

Tempering heats (for DRAWING the hardness) are as low as 300 to 400 degrees. The "blue" oxide color or spring temper is made by the higher temps as stated by J.T. at about 700 degrees, and are about as soft as you can temper without going into the incandescent heats that will result in "glass hard" hardening.