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Old 12-23-2016, 04:45 PM   #1
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drill bits

Wondering what most consider the best metal and coating for drill bits designed to drill hard metal such as high grade bolts abd stainless?

Seems like nothing I have tried in the past were either good enough or good enough quality.

I am especially interested in left handed bits also for drilling out broken bo,ts/stids.

The thequest is based on....guess whose alternator bracket forward bolt sheared off on his 120 lehman today?

When I get someplace for a permanent fix....I will try locktite as this gave no warning but looked like fatigue shear.

Check them for tightness before and during long trips....I just had them out as I changed alternators so they were snug only about 120 hours ago.
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Old 12-23-2016, 04:55 PM   #2
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Greetings,
Mr. ps. Yup, loose nuts. Not good for man nor machine...One would like to think that a "name brand" drill bit would be better than a no-name but with the global economy, both could easily be made in the same factory and simply branded differently. I can't help you with toughened coatings or the "best" but I can attest to the utility of LH drill bits. Saved MY bacon on a couple of occasions. Slow speed and lots of oil..oh yes, and patience.
I have been cautioned in the past NOT to use a harder bolt than necessary. If and when a class 8 or 10 bolt breaks they are a real pain to drill out. Don't ask how I know.
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Old 12-23-2016, 05:03 PM   #3
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drill bits

I'm sure I'll be in the minority on this thread but after trying most every drill bit material/coating my winner is...

Standard run of the mill high speed steel drill bits. Technique is more important than material IMO.

Fastenal has a decent quality index in the $50 range that provides the basic sizes in good enough quality steel for my general use. YMMV
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Old 12-23-2016, 05:06 PM   #4
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Lubrication Lubrication Lubrication Lubrication

The right Lubrication when drilling SS or any other metal is critical for both cooling and friction reduction. Dont just use any oil sitting around the workshop and expect it to cool and Lubricate the drill bit .
As RT would say the correct Lubrication is good for both man and machine

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Old 12-23-2016, 05:10 PM   #5
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Thanks RT....these were bolts into a threaded bracket that is part of the engine block.

Didn't get it out or a clean drill through.....so I will be over sizing the holes and using bolts and nuts.

But for future fiascos....just wondering as the variety I have used has been poor to slightly better.

Someone here suggested a nice easy out kit from Amazon...worked great on some broken screws...thought I hit the jackpot. The one I tried on this bolt sheared off half of its head in the bolt and drilled hole. Thus making the remaining drilling nest to impossible to get perfect.

This is the one part of tools that I believe I will spend a good chunk if I feel they live up to a great reputation. Many tools don't get the use or are non critical.

This bolt was a show stopper as with no alternator, the dang lehman and goofy coolant hose won't even allow a n emergency fan belt to bypass the alternator and drive the coolant pump.

So I would have dropped a cool $100 bucks on a bit if I thought it would have done the job.
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Old 12-23-2016, 05:15 PM   #6
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The Rigid brand of cobalt bits from Home Depot did a great job on drilling stainless stanchion tubes...but just didn't want to bite in this application.

Maybe it was the broken easy out that was causing all the slipping off center....
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Old 12-23-2016, 05:26 PM   #7
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Walter's brand makes a HS drill bit set. Many machinists use this brand. Pricey but high quality.
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Old 12-23-2016, 05:26 PM   #8
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drill bits

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The Rigid brand of cobalt bits from Home Depot did a great job on drilling stainless stanchion tubes...but just didn't want to bite in this application.

Maybe it was the broken easy out that was causing all the slipping off center....


Bingo

That broken easy out is gonna rock your world. A broken tap is much easier to deal with.

Try a couple opposite direction hammer blows with a center punch. If you remove the extractor drilling is a breeze.
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Old 12-23-2016, 05:51 PM   #9
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As has been mentioned Cobalt is the type of drill you want to use.
Use a drill press if you can. Cobalt drills are very hard which makes them brittle. If you don't keep them straight, they'll break.

Don't let the stainless get hot. It can suddenly harden even more and refuse to be drilled. I've only had this happen a couple of times but it's really strange when it does.

I use Century brand bits, mainly because they're good and I have them in my store.
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Old 12-23-2016, 05:59 PM   #10
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As has been mentioned Cobalt is the type of drill you want to use.
Use a drill press if you can. Cobalt drills are very hard which makes them brittle. If you don't keep them straight, they'll break.

Don't let the stainless get hot. It can suddenly harden even more and refuse to be drilled. I've only had this happen a couple of times but it's really strange when it does.

I use Century brand bits, mainly because they're good and I have them in my store.
Parks...got any left handed sets too?

Maybe when I stop long enough say at Ft Pierce I may be interested.....or when passing through your area in early march.
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Old 12-23-2016, 06:17 PM   #11
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I like just the standard drill bits that you get at a industrial type supply house. The gun metal dark gray ones . The are easier for me to sharpen . Tap Majic is some good oil also . If it's not cutting and bringing out a chip the metal is usually getting harder . Stop and sharpen the drill . Don't keep pushing if it ain't cuttin . A high speed center drill helps to get the hole started straight . They are ground to a perfect center and won't walk on you .
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Old 12-23-2016, 06:21 PM   #12
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Almost everyone drills too fast and quickly overheats the drill bit and ruins it.
The trick is to use constant pressure and slowly increase the speed of your variable speed drill until slivers of metal begin curving up from the hole you are drilling. It's important to use oil but more important to use the correct speed.
You might be suprised at how few rpms are needed to get the job done.
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Old 12-23-2016, 06:23 PM   #13
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It never hurts to have top quality drill bits for the important holes.

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Old 12-23-2016, 06:28 PM   #14
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If it's not drilling and the metal seems to be getting harder and harder and won't drill anymore you can always try carbide . But if you break it off in the hole you're pretty much screwed .
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Old 12-23-2016, 06:37 PM   #15
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If it's not drilling and the metal seems to be getting harder and harder and won't drill anymore you can always try carbide . But if you break it off in the hole you're pretty much screwed .
Is carbide harder than colbalt?

Is there a good sharpener that will do different cutting angles and all metal bits?
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Old 12-23-2016, 06:40 PM   #16
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It never hurts to have top quality drill bits for the important holes.

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Thanks for the link.....do you prefer one brand?
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Old 12-23-2016, 06:57 PM   #17
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For drill bits carbide or cobalt would be my choice but as said before whatever the material you need to do it the right way. If you try to drill a 3/4 inch hole in hard steel right away you will just cook your drill bit.
For LH bits again you need to do it the right way, the bit itself is just to be stuck in a pre drilled hole and remove your broken/stuck screw/bolt.
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Old 12-23-2016, 07:09 PM   #18
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For drill bits carbide or cobalt would be my choice but as said before whatever the material you need to do it the right way. If you try to drill a 3/4 inch hole in hard steel right away you will just cook your drill bit.
For LH bits again you need to do it the right way, the bit itself is just to be stuck in a pre drilled hole and remove your broken/stuck screw/bolt.
Is there some documentation that says you have to start with a regular drill then switch to left handed?

A load of machinist posts just say start with left handed drills, starting small and working your way up.
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Old 12-23-2016, 07:11 PM   #19
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Thanks for the link.....do you prefer one brand?
For most of what I do Hertel bits are fine. If I was running a machine shop, I would probably investigate it more.

As important as having a good drill bit is, being able to resharpen it or replace it is probably as important. Bits start dulling with the first hole. A dull drill bit is a good way to work harden an area you're trying to put a hole in.

Interesting story:
I was given most of my bits. Buddy of mine worked for Dupont doing maintenance and custom fabrication for research projects. Not sure they use anything but stainless steel at the research station. Anyway, they're only allowed to drill 3 or 5 hole with a drill bit..........then they throw it away. If you measured holes after that they will be slightly larger as the bit starts to wobble. Dupont determined it wasn't cost effective to resharpen bits. Same for taps. I found it was cost effective to resharpen their discards.

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Old 12-23-2016, 07:13 PM   #20
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Greetings,
Mr. ps. I think you could probably start with either direction drill while working your way up in increments BUT at some point you would have to change over to your LH bit. I see no advantage either way.

Allow me to amend that last statement slightly. IF you use a series of LH bits you will be constantly "unscrewing" as you drill.
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