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I recently made some pins for a project at work using a coil spring. I'm assuming it is 5160. After great treating and tempering them I realized that I need to drill and tap the ends of the pins for a 1/4X20 screw and in their hardened state they wear out my drill bit really fast (obviously). So now I need to aneal them. This is where the problem comes into play. I do not have a forge here, so I can't use the technique of heating them up, and then cooling them down slowly in the forge. I am thinking about trying the following technique but wanted to run it past you gurus to see what you thought. 

Fill a metal bucket with dirt leaving a cavity in the center. 

Heat the pins to critical, at the same time preheating the dirt with a propane torch. 

After that I would bury the pins in the hot dirt and leave to cool slowly. 

Does this idea make sense? 

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A better annealing medium is something such as wood ashes or vermiculite (available at nursery or garden shops). You don't need to preheat either of those, BTW.

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Just try heating with a torch and draw as much of the hardness out as you can. Are you using good quality HSS taps and drills?

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The problem with the idea like this is once they are tapped for the 1/4X20 they usually have enough distortion that the bolts never go in right once heat treaded.. I'm guessing you are using 5160 coil springs so the diameter is pretty small..  I could be wrong.. 

The way I do it in the past was to forge, anneal, drill, tap,  then insert a bolt that caps off the end of the bar where it's threaded.. I cover the bolt with white out or in the past used charcoal powder or graphite powder..  

Then heat to critical and oil quench..    Then remove the bolts..    This seems to stabilize the hole some vs being thin walled and then into oil which shrinks and hardenes the threaded end much more so than the solid end.. 

 

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I realize that there are better annealing mediums out there, but like I said this is being done at work with only typical welding/shop tooling IE no forge or any of that fun stuff which is why I thought I'd try and get as much heat into the dirt as possible because I am sure it isn't as good of an insulator as ashes or vermeculite.  I used a half bucket of dirt, put a 1/2" plate in the dirt and heated the pins on top of it then buried them and tamped it down.  My goal there was to get some extra heat in the plate to allow for a slower cool down of the pins themselves.  Tomorrow morning when I get to work I'll pull them out of the bucket and try drilling them in the lathe.  I'll let you guys know how it worked out.

14 hours ago, BIGGUNDOCTOR said:

Are you using good quality HSS taps and drills?

My taps are good, however the drill bit we have for 1/4 20 taps has seen it's better days.  I drilled and tapped 2 pins the other day and I had to sharpen the bit 5 times! 

13 hours ago, jlpservicesinc said:

The way I do it in the past was to forge, anneal, drill, tap,  then insert a bolt that caps off the end of the bar where it's threaded.. I cover the bolt with white out or in the past used charcoal powder or graphite powder..  

Thank you for this idea!  I was planning on running the tap through them again after heat treat and temper, and probably still will, but this will surely help reduce the amount of cleanup needed.

tempering is a heat treat

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I"m assuming you are tapping them manually by hand?     If you are using a machining center it's a little different story.. 

A carbon hand tap will not cut threads in hardened 5160 unless it's drawn to a blue or green and even then it will ruin the tap.. 

A high speed steel tap will fair a little better depending on quality.. 

There are taps out there now that will thread hardened 5160 but personally have never had any luck with them since i hand tap vs machine tap.. 

1/4X20 to me in hardened material is just a problem without a machining center and a proper time, lube, etc, etc.. 

Remember a file will skate on hardened 5160 so a tap is not quite as hard as a file.. 

And back to your original question..  Even normalizing them will give you a normal state and 5160 will drill ok and even tap ok.. But being as soft as you can make it would be better.. 

Cooling in sand or dirt will work as long as there is no moisture in the dirt or sand. so heating it with a torch would be good. some sand or dirt will stick to the metal at transition temperature so this can be a concern if it is a finished product..  ideally even a small box painted black and left in direct sunlight on the tar or asphalt will work well if done at noon time in a warm enough climate.  The idea is to cool it very slowly.. Slower the better..  Some would say to hand holding temp..
 

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2 hours ago, jlpservicesinc said:

1/4X20 to me in hardened material is just a problem without a machining center and a proper time, lube, etc, etc.. 


I am drilling out in the lathe and then taking by hand using the lathe to keep it centered. 

2 hours ago, jlpservicesinc said:

Remember a file will skate on hardened 5160 so a tap is not quite as hard as a file..

This is why I'm annealing them. I was trashing my bit and scared that is leave half of my tap in the pin.

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I just normalized a hay rake tine made into a steel striker.  I used a bucket of white ashes from the stove.  I plugged it right in there and put the lid on it.  Because it was so thin, by the time I cleaned up the shop it was annealed.  It was still hot to the touch, but a file easily dug into it.  The ash bucket works, but just make sure it's all white ashes without anything in there that could catch on fire.  My ash bucket is an old family hand-me-down from our wood stove heating days so the lid seals the ashes off good from oxygen.  I'd want that kind of set-up if I were going to walk away and leave it and walk away.

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Sorry I left information out..

 

What I was trying to say is..  you will get shrinkage and distortion when you harden them.

A tap ran into a hole after hardening maybe a problem.. you might be safe..

In hardening ive seen holes like thst go oval. And a tap is useless..

It's the reason I suggested using white out or charcoal or graphite on the bolts inserted before hardening..

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56 minutes ago, jlpservicesinc said:



I understood why you were suggesting filing the holes with bolts. But thank you for clarifying anyway! I know that it is impossible to know the experience or knowledge base of many of us newer members and you are being responsible by "breaking out the crayons" and explaining the "what" and the "why".

I've been a welder/fabricator/machinist for a number of years and have a good understanding of metal it's very nice to be able to combine my knowledge with the wealth of knowledge and experience on this forum. Thank you all! 

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