Drilling advice needed.

I usually somehow manage to remove a broken bolt but in this instance that is not an option so I need to drill it out. The bolt is probably hardened steel and I am using a drill press at 300 RPM, a cobalt bit, and metal cutting oil. I have had the drill press arm bungee tied for the past few hours and all I got was about a millimeter. Is this normal or am I doing something wrong?
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Does your drill press do left? Can you use a reverse fluted drill bit?
Christopher A. Young Learn more about Jesus www.lds.org .
I usually somehow manage to remove a broken bolt but in this instance that is not an option so I need to drill it out. The bolt is probably hardened steel and I am using a drill press at 300 RPM, a cobalt bit, and metal cutting oil. I have had the drill press arm bungee tied for the past few hours and all I got was about a millimeter. Is this normal or am I doing something wrong?
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After doing extensive research here is how I drilled-out a hardened steel bolt:
1.    Use a drill press that has a vise. It says to use a hydraulic chuck instead of a clamping chuck but I didnt have a hydraulic chuck; maybe I got lucky that it worked for me. 2.    Set the drill for 220 RPM 3.    Use lots of cutting oil. 4.    Feed the drill VERY slowly and no more than several seconds at a time. Clean out bits of steel with a paper towel between periods of cutting; maybe its not necessary but doesnt hurt. Keep the room as quit as possible so you can hear it cutting. 5.    Use a solid carbide bit. Not carbide coated or carbide tipped but solid carbide which costs about $22.00 for a diameter bit. The bit is very brittle and will break very easily and can never be sharpened. Do not expect it to give at all. You will not find a solid carbide bit in any hardware store so dont even ask because they wont even know what youre talking about. You will need to go to an industrial tool supplier or the internet.
I must be the first to post these instructions on the internet because I havent seen another one with this much detail. Bully for me.
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On Tue, 15 May 2012 15:48:30 -0700, Molly Brown wrote:

Yes, the more solid the thing you're trying to drill into, the better (not that drilling metal without having the workpiece clamped is ever a good idea, anyway).

Well, on the one hand you don't want to overheat it - but on the other, doesn't most drill bit wear occur when first getting the bit to 'bite', rather than once it's cutting? So perhaps stopping frequently is actually a bad thing in terms of the life of the bit.

I've not tried those, but I do have some cobalt bits which have been serving me well - for the larger diameters it's necessary to start out with a smaller bit and work up to the desired diameter, though.
cheers
Jules
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On Sun, 13 May 2012 17:55:36 -0700 (PDT), Molly Brown

Sounds like it's time for EDM.
http://en.wikipedia.org/wiki/Electrical_discharge_machining
Some automotive machine shops provide the service.
--
croy

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On 5/13/2012 7:55 PM, Molly Brown wrote:

I doubt that your bolt is hardened. It may well be stainless steel which can be vicious to drill. It is regrettable that you have work hardened the bolt by "grinding" it. Really slow speed, lots of pressure. If the bit is not cutting chips or curls, stop! continuing to work harden only makes things worse. Stainless steel is VERY prone to gauling and once it happens cannot/will not thread in or out. Drill and retap or alternate assembly become the only choices.
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It is spelled galling. Difficult for me to explain, but it is when the threads sort of lock up and almost 'cold weld' to the bolt hole.
http://www.estainlesssteel.com/gallingofstainless.html
While it hapens to other materials, stainless steel is the most common seem one that has this as a major problem.
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On Wed, 16 May 2012 06:47:23 -0700 (PDT), Molly Brown

Not all grades of stainless are non-magnetic. Not a good test.

Kinda like spaulling. ;-)
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Define "better". ;-)
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Insufficient information. Non-magnetic may be gooder. On a different day, magnetic may be even more gooder.
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I suppose after you take it out, you lubricate it with WD-40, too.
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Use a magnet and choose the non-magnetic.
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On Wed, 16 May 2012 06:47:23 -0700 (PDT), Molly Brown

Some info on "stainless steel" and "galling" is available here:
http://www.estainlesssteel.com /
More good stuff here:
http://www.aksteel.com/pdf/markets_products/stainless/Stainless_Steel_Comparator.pdf
--
croy

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While in general the non-magnetic stainless steels have greater corrosion resistance than the magnetic varieties, "better" is relevant to the intended use. The magnetic stainless steels are often harder, stronger, or have other characteristics that make them preferable in a specific application. It would be incorrect to say one type is better than another only on the basis of magnetism without also considering how it will be used.
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Sometimes shit can be spectacularly and anomalously hard. For example, I was trying to drill/tap some holes in the ends of a dumbbell for an eyebolt. One drilled fine, the other was like glass, absolutely un-drillable.
A carbide bit might help, but maybe you just have to heat the thing red hot, and let it cool slowly (cover with sand or sumpn), to anneal.
Also, some stuff is superhard, but just on the surface, as in case-hardening, while the interior is softer, sometimes very soft. If you try grinding away 1/16 inch or so, you might find it much easier to drill.
I wonder if they make a "grinding drill", which would basically be a rod coated with aluminum oxide, to just grind a hole through.... which could be a very slow process. You could run this idea by the folks at rec.crafts.metalworking.
I doubt a bungee cord is doing anything but dulling the bit.
--
EA




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