Drilling hardened steel?

Jumpmaster

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Hello again, kind folks...I have another potentially stupid question. :)

I've just about finished cleaning, lapping, and adjusting the gibs on my 7x10 mini lathe. The wheels turn much more nicely now. I've also been watching a lot of videos and understand a LOT more about my lathe than I did before. For instance, I learned that what I was calling "slop" in the feed wheels is actually called "backlash"...and I understand how to work around that now...and maybe how to minimize some of it.

Anyway, I'm writing now to ask if I'll be able to drill a piece of 0.5" hardened steel with my lathe. I've learned (I think) a few things on this...

First, I've read in several places that you cannot drill hardened steel without "special equipment". I do not know what equipment that might be.

Second, I am almost certain this piece I want to drill is hardened...I tried cutting it with a file and it didn't do anything to the steel.

Third, ideally I would like to drill it straight through its diameter so that I can fit a piece of 550 cord through the hole. I saw that the best way to do this with a lathe is with a V block...I know a mill would likely work much better, but I do not have a mill...yet...:D

Finally, I'd like to face the end...this piece of metal was an old punch that broke off...no real use for it other than sentimental value...I've closed hundreds of parachutes with that little chunk of steel. :)

As always, I greatly appreciate everyone kindly sharing their experience with me and helping with questions like this. Everything I've stated above is stuff other people have stated that I've read or heard; that doesn't mean it's correct...I will obviously defer to your direct experience, which I know is vast. :)

Thanks in advance!
 
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will

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The only work I ever did ( years back ) with hardened steel is grinding it.
 

smokinbasser

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A good nitride drill can drill into/through hardened steel but you need to use moderately slow speeds and light downward speeds. I suggest you acquire some tapping fluid and apply it frequently to keep the bit "cool"
 

precisionworks

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Sharp tools turned at 25 sfpm are a good start. I've run drills at 10 sfpm in some steels. Buy the drill or drills from a manufacturer like Guhring, Dormer, Precision Twist, etc., & superb tech support is part of the package.

I recently bought some high dollar twist drills to work in Ti-6-4 & had issues with heating, hole shrinkage, etc., while running 25 sfpm. Called tech support & they suggested 75 sfpm with heavy feed. Worked like a charm.

Too fast is bad, too slow isn't any better and every combination of tool & material has an optimum speed & feed. Find that & life is much better. Good twist drills are expensive & cheap ones are cheap for any number of reasons.
 

FlashKat

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Just remember if you use a carbide bit that you know carbide is brittle, and it should be used at higher RPM with light to moderate feed rate. Carbide can take the heat, but not the pressure. Carbide will cut right through a file.
I'm not really sure what you're asking. If you're asking what alloy it is, I have no idea. If you're asking what form it is, it is a short, round rod.
 

Jumpmaster

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Yes, I read that you have to use carbide at high speeds...and also because it is brittle, it can shatter at those high speeds.

But it's ok...I have a full face shield for use with the lathe (with safety glasses under that. :) ) I have a friend that lost an eye due to an accident in his shop...I am VERY careful with my eyes. :)
 

FlashKat

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The RPM does not need to be super fast :)
Yes, I read that you have to use carbide at high speeds...and also because it is brittle, it can shatter at those high speeds.

But it's ok...I have a full face shield for use with the lathe (with safety glasses under that. :) ) I have a friend that lost an eye due to an accident in his shop...I am VERY careful with my eyes. :)
 

hoop762

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Ive had good luck drilling through Russian AKs with a quality drill bit, slow speed, and plenty of lube. I use motor oil and apply it with a syringe and an IV catheter for precise application with very little mess.
 

NoNotAgain

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First thing if you're attempting to drill thru the center of a piece of material on a lathe is to make a flat on the surface that is closest to the lathe cross feed.
Secondly, purchase a starter drill, it's very short and rigid, which is needed to get a hole started. It doesn't have to be deep, just enough to keep the twist drill from walking around.
Third, a cutting lubricant containing sulfur will make cutting steel much easier.
Forth, you want a drill bit with a point angle of at least 135 degrees. The flatter the drill on hard materials the less point load.
Fifth, your lathe being a belt change for speed is going to be dependent on feed rate more so than speed.
Finally, chuck your drill bit up as short as possible, and slowly enter the material and then back off to clean the chip before re lubing and drilling again.
 

brickbat

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There is come chance this 'old punch' is made from carbon steel. In that case, it's a relatively easy matter to anneal it. Annealing it would render it plenty soft to easily drill it. Basically - heat to to 800C and cool it very slowly.

(If it's high speed steel, annealing is much harder)

Another approach is a specialized drill - carbide maybe? I've seen these demo'd at shows, where the guy drills through files and such. These drills are run very fast, the friction heats the object - softening it, allowing the drill to work.
 

PeterH

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Annealing steel is fairly straight forward, heat to a dull red and cool slowly. This will make machining much easier. The tricky part comes with hardening it again, presuming you need it hard when finished. Hardening is some variant of heat and quench, but how hot and what to quench in depend on the alloy. As does tempering afterwards to avoid brittleness.
 

sortafast

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Annealing steel is fairly straight forward, heat to a dull red and cool slowly. This will make machining much easier. The tricky part comes with hardening it again, presuming you need it hard when finished. Hardening is some variant of heat and quench, but how hot and what to quench in depend on the alloy. As does tempering afterwards to avoid brittleness.
I was doing a tac knob for a savage bolt gun. It was hard as heck so I heated it as hot as I could with a propane torch then put it into a coffee can full of new kitty litter I use for oil spills. I think I let it cool for an hour or so. Worked like a charm was super easy to machine after that.
 

Jumpmaster

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Well, I have to say my first attempt did not go very well. :)

Nothing broke, but...I think I may need to try to anneal it as described above and try again.

Also tried turning some aluminum. Worked ok, but I really need to cut these bars down. They're 6" long and the chuck I got for the tailstock (which is apparently made for this lathe) is way too long to be able to center drill a 6" bar. I'd planned on center drilling these bars and using the live center to support them, but I guess I'm going to have to cut them shorter.

Then I found that even though mini-lathe.com said the spindle hole should be large enough for 3/4" bar stock to pass through, in reality it is not.

A kind soul gave me some sage advice which I will probably take which was to get an adapter plate and a 4" chuck. I think I will do this relatively soon.

Thanks for the advice on drilling this hardened bar, everyone...one way or another, it *is* going to be drilled at some point. :)
 

PEU

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If its carbon steel, heat it to 700~800C, a magnet will be your reference, if it doesn´t stick its there, then drop it into ash or something that can slow its cooling rate, then drill, it will be soft. If you need it hardened again, heat it again to non magnetic, wait 30 seconds while still heating it and drop it in oil, almost any oil will do, if its kitchen oil you will have less residue than motor oil.
If its stainless, cooling needs to be much slower as most stainless air harden.
This is a simplified explanation, for accurate explanation google annealing carbon steel, for example Bohler K720 (carbon) or for stainless Bohler N695, look for the annealing section.


Pablo
 

gadget_lover

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Based on the first post, you want to drill across the rod, not down the center. A good way to start is to make a flat spot on the side of rod. That's assuming you have the rod clamped in the chuck. Then use a carbide spotting drill to start the hole. They are short. Then you can use a "screw machine" drill to drill the hole. As an alternative, use a center cutting carbide end mill in the tool post.

Daniel
 
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