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Author Topic: Drill bit for hardened steel  (Read 737 times)

spclark

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Drill bit for hardened steel
« on: December 21, 2016, 03:51:08 PM »
I make hammers for the Marauder.  The most recent one is being made out of some sort of 1.25" axle shaft.  I turned it down to diameter on the lathe with no issues, and drilled thru for the striker hole and spring counter bore with no problem.  When I went to cross drill it for 8-32 and 10-32 tapped holes, the cobalt drill wouldn't touch it.  What type of drill bit do i need to drill this HARD steel?



Alan

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Re: Drill bit for hardened steel
« Reply #1 on: December 21, 2016, 04:42:47 PM »
They are case hardened, so I suspect a diamond drill.
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Alan

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rsterne

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Re: Drill bit for hardened steel
« Reply #2 on: December 21, 2016, 04:43:29 PM »
I would try a Carbide bit.... or anneal the hammer by heating red hot and allowing to cool slowly....

Bob
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Madmullet

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Re: Drill bit for hardened steel
« Reply #3 on: December 22, 2016, 05:02:31 AM »
I dabble in knife making and a few times I have had to drill a blade after it has been harden and heat treated to 60-61 rockwell.  The only thing I found that worked was Pure carbide drills from a company called Drill America.  They are not cheap about 20 to 150 bucks each and very brittle so use them in a drill press on low speed or in a trusty Ol bridgeport.  I cant see a axle being supper hard I would look in to a set of HSS drills first. 
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spclark

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Re: Drill bit for hardened steel
« Reply #4 on: December 23, 2016, 04:06:57 PM »
are HSS bits 'better' than cobalt for hard steel? 

marmot_militia

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Re: Drill bit for hardened steel
« Reply #5 on: December 24, 2016, 06:31:54 AM »
You will have to anneal it.  If you think drilling is hard, wait till you try to tap it.

As noted above, heat the area to red hot and let it cool slowly.

Jim

rrdstarr

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Re: Drill bit for hardened steel
« Reply #6 on: February 23, 2017, 07:55:01 PM »
Bingo!
lots of cutting fluid and slow speed also!
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Gerard

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Re: Drill bit for hardened steel
« Reply #7 on: February 23, 2017, 10:45:50 PM »
Some steels also work harden, especially some stainless alloys. You need to take it very slow with light pressure in such cases or you end up snapping off the drill or tap just when you are almost through... ask me how I know. Especially fun when you have invested several hours' work into a complex piece of metal and you now have a hardened tool bit broken off inside a criitical hole. One learns about ways of shattering such bits and picking out the nasty little pieces... really not fun at all.

Often goes well however. I had a stainless block to tap for my scientist brother a couple of years back. Part of a vacuum rig for low pressure cell culture incubation or something. Worth about $4,000, this really precisely made piece of equipment. He needed a larger hole to thread into for a higher rate of air pumping. Had to tap it to 10-32, about 1/2" in. I drilled out the smaller threads then grabbed my lucky 10-32 tap, one I've used for many years and had recently sharpened. After about half an hour and going maybe 1/20th of a turn at a time backing out then oiling then going another 1/20th etc, the hole was finally deep enough for the connecting hardware and I could stop having a slow motion heart attack. The very next time I used that tap it snapped off. On something which didn't matter at all. Guess I got very lucky. I'll stick to newer taps next time something like that comes along.
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