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How to Ruin a Drill Bit

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Words of Drill Bit Wisdom

Drilling metal is a frustrating and time-consuming task.  If not done correctly you can quickly ruin a drill bit.  I have personally ruined about 100 drill bits so I know what I am talking about.

The #1 problem is a dull drill bit.  All new drill bits start out nice and sharp however if they are not used correctly they will quickly become dull.  I can ruin a new drill bit in about 60 seconds!  So what happens to make a drill bit dull?  OVERHEATING.

Feed is how hard you press

Speed is how fast the drill spins.

If the feed is too slow (not pressing hard enough) the drill bit will not bite into the metal, it will just spin without cutting very much.  This causes a lot of friction, which overheats the drill bit and makes it dull.  Too much pressure on the feed will also overheat a drill bit (and make it dull).  In my experience it is hard to give too much feed with a hand drill unless you have a small bit.  You will know when you press too hard with a small bit because it will break.  It is always better to press a little too hard, a light feed will cause the bit to overheat and get dull.  (a small drill bit that is dull cuts about as good as a small bit that is broken)

If the speed is too fast (the drill spins too quickly) the drill bit will not bite into the metal, it will just spin without cutting very much.  This causes a lot of friction, which overheats the drill bit and makes it dull.  If you run the drill too slow, it will just take longer to cut.  GO SLOW!  You will ruin all your drill bits if you use a drill that has only one speed.  Make sure you have a variable speed drill.  Big drill bits require slower speeds than small drill bits.

The #2 problem is a cheap drill bit.  There are many ways to make the tips extra hard so they stay sharper longer.  It should come as no surprise to find that more expensive drill bits last longer and cut better.  I like bits that have a Titanium Nitride (TiN) coating.  You can tell if they have this coating as the tips look like gold.  They cost as much as gold and will still get ruined by using the wrong speed and feed.  (Don't loan them to your friends.)

Most drill bits can be sharpened.  A highly skilled technician can sharpen a drill bit with a grinding stone.  Almost every skilled technician has ruined about 500 drill bits before they develop this skill.  Grinding stones will quickly overheat a drill bit and it will lose it's temper.  Not only does this make the drill bit mad, it makes it soft.  Then it makes you mad because it gets dull again real quick.  In fact drilling at too fast a speed, or too light a feed will also cause a drill bit to get hot and lose it's temper.  After a drill bit has lost it's temper it will not stay sharp.

The other problem with sharpening a drill bit is getting grinding the tip slightly off center.  The point of the drill bit must be exactly in the center of the tip.  If it is off, even a little, the drill will wander and cut a larger hole than it should.  In my humble opinion the only way to reliably sharpen a drill bit is with a special drill bit sharpening tool (like the drill doctor).

The #3 problem is a cheap drill.  Cheap drills often only have one speed and spin way too fast for drilling in metal.  (did I say too fast a speed will overheat a drill bit, make it dull, ruin the temper, and cause it to quickly get dull again after being sharpened?)  Cordless drills are way cool and very convenient however if they are not powerful enough, they will not be able to keep turning at the proper feed rate.  (did I say it is better to press too hard than too lightly?)  An inexpensive cordless drill will not have the power you need to drill metal with a strong feed and a slow speed.  Usually a cordless drill with a higher voltage battery will be more powerful.


Here are my recommendations for happy drilling

#1  Buy a high quality drill with a variable speed

#2  Go SLOW.  Too slow is way better than too fast

#3  Push Hard.  You should see metal chips actively coming away from the bit

#4  Use cutting oil (reduces friction and caries away heat)

#5  Buy good quality drill bits

#6  When a drill bit gets dull, throw it away and get a new one. (time is money)

#7  Use a center punch (you will figure this one out very quickly)


Often you are using the drill to remove a bolt that has busted off.

To do this you drill a hole into the busted bolt and hammer in a screw extractor.  Once in place you turn the extractor counter-clockwise to remove the bolt. 

The first mistake beginners make is to not make sure they are drilling in the exact center of the busted bolt.  Careful use of a center punch is critical to getting your drilled hole centered.  Also pay very close attention that your drill is lined up square!

The best type of drill bit for this operation is a LEFT HANDED DRILL BIT.  They cut as the drill spins counter clockwise.  (most drill bits cut in the clockwise direction)

If you use a slow speed with a good hard feed pressure you might get lucky and the bit will grab the busted bolt hard enough to spin it right out.

Once the hole is drilled you then hammer in the screw extractor.  There are a variety of styles with "easy out" being a very popular style.  I personally find screw extractors that are straight and not tapered to be far superior. 

I strongly recommend you study this link for details on the best method to remove a busted bolt.

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