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Old 03-06-2012, 11:21 PM
zuren zuren is offline
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Default Drilling/grinding hardened steel?



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I have a decent assortment of tools but this issue stopped me pretty quick from lack of experience. I have some older seat belt floor brackets that already have a 1/2" hole in them. I believe they are hardened, Grade 8 steel. I want to open that hole up to 9/16". I thought this would be a simple task for an Irwin Unibit, my drill press spinning at 690 RPM and light pressure but it stopped cutting pretty quickly. I was doing this without lubricant and I'm not sure if I ruined the 9/16" step on the Unibit but it still looks and feels sharp.

Should I try again with the Unibit and some cutting oil? I have 3-in-1 All Purpose oil but could go get some dedicated cutting oil. I've also read turpentine works to help cut hardened steel. I'm also willing to go out and get a better bit to do the job; was just hoping to use what I have.

I have a Dremel with grinding wheels that I could use as well. It won't be as neat but would probably work. I'm jut not sure what the best approach should be.

Thanks for any advise!
Old 03-06-2012, 11:46 PM
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I think a standard HSS twist drill would work better than a step drill.
Old 03-07-2012, 12:06 AM
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If you heard it squeak you have a problem. I would use your dremel. Go around the hole and if the grinding bit is small go in and out at the same time to use the entire surface of the grinding media.
Old 03-07-2012, 04:26 AM
Borsch Dorks Gorge Borsch Dorks Gorge is offline
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The dremmel is the answer. I had this a few years ago when a track rod end bolt had seized into a steering arm. Heat, various drills and drill press and a milling machine would get no-where. You could get a 6mm HSS bit through it, anything bigger just would not play.

As it was a few hundred for a new arm, used the dremmel, took a long time. An air die grinder would do the same job. Make sure you buy decent stones. I have found the dremmel knock off ones to be completly inferior to the genuine dremmel stuff and likewise with stones for die grinders, you get what you pay for.
Old 03-07-2012, 05:08 AM
5H4N3 5H4N3 is offline
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Buy a 9/16 tapered reamer, and you can turn them out like an assembly line.
Old 03-07-2012, 05:18 AM
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hss drill bit .... clamp it down tighter than h*ll .... cutting oil and give it plenty of relief .... clear away the chips and keep the bit/metal temp down .....
Old 03-07-2012, 10:58 AM
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Get a carbide ball nose endmill. Clamp your part down good on your drill press it will cut it with no problem. Not cheap but fast if you have several to do.
Old 03-07-2012, 04:38 PM
zuren zuren is offline
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The Dremel did the trick! It took a little time for the 4 I had to do but a grinding wheel and some patience removed the material I needed.

For future reference, would a cobalt step bit have worked? The unibit I initially tried was non-cobalt:

http://www.irwin.com/tools/drill-bit...alt-step-drill

I have one Irwin Cobalt unibit but it was too small for this job. The one's in the link are listed as Cobalt HSS.

Thanks for the help!
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Old 03-07-2012, 04:47 PM
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Quote:
Originally Posted by zuren View Post
The Dremel did the trick! It took a little time for the 4 I had to do but a grinding wheel and some patience removed the material I needed.

For future reference, would a cobalt step bit have worked? The unibit I initially tried was non-cobalt:

http://www.irwin.com/tools/drill-bit...alt-step-drill

I have one Irwin Cobalt unibit but it was too small for this job. The one's in the link are listed as Cobalt HSS.

Thanks for the help!
I would have used the drill press at lower RPM, taking my time, and lubricated the material. I don't have significant experience on hardened steel, but have lots of time on the handy dandy drill press. Most of the hardened steel I've cut (not having to open a hole from 1/2" to 9/16") was with a plasma cutter or hydraulic shear. Depending on how badly you needed the part, maybe a machine shop could have punched the holes for you.
Old 03-07-2012, 05:29 PM
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Good job. The problem I have with step bits is you can't drill deep holes. A cobalt one might work, hard to tell when working with hardened good steel.
Old 03-08-2012, 10:05 AM
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CUTTING OIL IS YOUR FRIEND!!!

You can get Oatey Threading Oil at the Home Depot for about $12.00 per quart.

I know that some experienced machinists might disagree ... but in a pinch or a survival situation ... most cooking oils will get 'er done. Friends of mine have said they've used PAM spray on cooking oil with very good results.

I'm thinking that bar oil for chain saws might be worth a try ... or maybe even chain lube for motorcycles. They are designed to hang on real good ... and stand up to pretty high heat.

I have a couple firearms that are fussy about lube and I have found that bar oil works GREAT on them. Just make sure to use just a couple drops ... and massage it in REAL good ... wipe off the excess.

oddshot
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Old 03-08-2012, 01:39 PM
equinelover equinelover is offline
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what is "hss" ? the only thing i can think of is hardened stainless steel but i know that is not it. have same problem. used two "metal cutting drill bits". both went dull i think. sit and spinn is about all they did. both brand new bits. thank you.
Old 03-08-2012, 02:56 PM
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Hi Speed Steel
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Old 03-09-2012, 03:01 PM
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On hardened steel,I like the cheap carbide masonry drill bits. The ones with the small flat carbide cutter. Slow speed with oil they cut really good.If they break(I said the cheap ones) toss it and get another.
Old 03-09-2012, 08:12 PM
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The biggest problem with cutting or drilling hardened steel (or any steel for that matter) is if you let the metal get to hot it will glaze (develop a layer that looks like mother of pearl) once that happens the metal will be to brittle to be of any use for any load bearing purpose as it will break when you need it to be strong.

Cutting oil should always be used unless you are using a grinder, file, or cutting torch.
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Old 03-10-2012, 01:50 AM
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Carbide masonry bit works pretty well for this kind of task, if you don't need a pretty finish on your metal. Step drills are usually intended for sheet metal work, and soft sheet metal at that. The thicker stuff is usually not easily handled by that tooling.
Old 03-10-2012, 11:55 AM
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You need to slow it down. If you can get down to 300RPM or so you'll preserve your bit and cut faster. The tapered reamer mentioned before is a great option, but not very cheap. Another way would be to heat the steel up and anneal it before you drill it, then re-harden it if you need that hardness for something. Seat belt brackets, whether hardened or not, have to be incredibly strong, like the steel in your brake pedal assembly. Other than that, you can grind it out with a Dremel or something like it as mentioned before.
Old 03-11-2012, 10:36 PM
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HSS is just hardened steel. Usually M2 or M42. Using it to cut a different type of hardened steel usually only gets you a trashed drill bit or endmill. Carbide drills/mills are what you need to machine hardened steel, and even with carbide you need to take it easy. At work, i regularly get jobs to remove broken drill bits or taps from holes. I use carbide tooling and really slow spindle speeds and high pressure on the bit. As far as cutting oil, i swear by used motor oil and use it more then anything. If you want a commercial oil that does a fantastic job, get a can of "tap-magic"

Solid carbide tools are cost prohibitive so a masonry bit can work in a pinch, but notice that the cutting edges are honed and not all that sharp. That works against you big time.
Old 03-11-2012, 11:14 PM
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There was an article in Popular Science or Popular Mechanics years ago that showed how to rig a jackshaft with about an eight inch pulley to a bench drill press. That really cut the rpms down and increased the torque. If I can find a picture of it, I'll see if I can't post it here.
Old 03-11-2012, 11:18 PM
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High speed steel drill bit of the appropriate dimensions with appropriate lubrication and slow speed will get you right through most hardened steels with little trouble.
Found this out after burning out too many bits and hole saws trying to drill and cut extremely hard steels. Use a good lube and keep the bit turning slowly!
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