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RPease
07-15-2008, 07:31 PM
:confused: OK...........I've got to ask............is there some "special" reason for having a left handed drill bit.

I saw some advertised and cannot figure out what they would be good for except for a broken drill that will "only" work in reverse........

A "hole" is a "hole".......whether drill clockwise or counter clockwise.........Right??

Can someone explain what they are for??

Thanks.............

Buzzer John
07-15-2008, 07:41 PM
one use for left hand bits is when you are drilling out a broken off bolt. A right hand bit will try to screw it in further, while a left hand one tends to unscrew it. If you are lucky (seldom happens) the broken bolt might come out when you drill with the LH bit.
I think there is another use, but can't think of it right now. John

Mark Hockett
07-15-2008, 07:41 PM
They are used for removing broken bolts. By drilling in reverse when the drill bites at the end of the hole if will spin the bolt out instead of in.

oldtiffie
07-15-2008, 07:44 PM
They are of course rotated "back-wards" - true - no joke!!

They are primarily for drilling out jammed or rusted bolts,studs etc. They will sometime cause the thread to "walk out". The principle is the same as "screw extractors" - aka "Ezy-outs".

It surprising how much concentration - for me anyway- when you've had a long time developing the skills and habits of sharpening right-handed drill bits!!

Frank Ford
07-15-2008, 08:03 PM
I understand left hand drill bits are used in some multi-spindle drilling machines where the adjacent chuck have opposite rotation.

loose nut
07-15-2008, 08:09 PM
Right hand drill bits for right handed people and left hand drill bits for left handed people, just like batters and golfers!!:D :D :D

Duffy
07-15-2008, 08:11 PM
Left-hand drills are used in gang-drilling machines-particularly those used to drill those rows of holes in the side panels for adjustable shelving. Every other drill is left-handed and this elliminates the need for an idler gear between drills, and allows closer spacing with a simpler gear box. Duffy

Optics Curmudgeon
07-15-2008, 08:15 PM
They are often used in the back side spindles of screw machines, for drilling the back of parts after they are cut off. I used to have a set of fraction and number lefties. Later, when I got to dealing with graduate students and PhD's they came in handy, just the thing to drive the "smart people" nuts. The time spent regrinding them was worth it.

Joe

KiddZimaHater
07-15-2008, 08:22 PM
What about left-handed allen wrenches? :D

gary55ford
07-15-2008, 08:50 PM
They are to drill holes for tapping left handed threads:D :D :D

Weston Bye
07-15-2008, 09:04 PM
I understand left hand drill bits are used in some multi-spindle drilling machines where the adjacent chuck have opposite rotation.

Indeed, I have seen such creatures.

RetiredFAE
07-15-2008, 09:32 PM
And here all this time I thought the left handed drill bits were for use south of the equator to counter act the Coriolis effect, you know, the way water swirls down the drain in a different direction down there, and that if you didn't use a left handed bit south of the equator, it would spin you into the ground.

And if you buy that, I have a big gold bridge I'd like to sell you too!

sch
07-15-2008, 10:29 PM
Left handed endmills are available for the same reason as Frank
Ford mentioned. Not for nothing are most single spindle mills
(as opposed to ganged mills) made with forward and reverse.

oldtiffie
07-15-2008, 10:49 PM
Dead right Steve.

Its "different down-under".

If you are gunna get screwed here it will be with a left-hand thread.

We have a good line in gold-bricks too.

wierdscience
07-15-2008, 11:04 PM
Multi-spindle drill heads

http://img.photobucket.com/albums/0903/wierdscience/MULTI.jpg

DR
07-15-2008, 11:51 PM
Left handed drill bits were developed for automatic screw machines. I can't remember the reasoning behind having the spindle rotate opposite to the direction of a standard engine lathe, but there is a sound reason.

Another use would be in multiple spindle drilling heads where the driving mechanism requires alternate bits to rotate in opposite direction.

Another newer requirement would be in slant bed CNC lathes with a rear turret. To take maximum advantage of the machine's rigidity the spindle turns opposite of normal. This direction is back wards for standard drills, so to save time of a spindle reversal left handed drills are used.

My guess is the secondary use like drilling out broken taps was not a big factor in development of left hand drills.

pntrbl
07-16-2008, 12:19 AM
I had to drill and ream a buncha holes thru the center of some SHCS's from the bottom. Made a simple fixture to hold the screw but the drill was running the screw out of the fixture ..... until I got a left hand drill bit.

SP

oldtiffie
07-16-2008, 12:24 AM
My guess is the secondary use like drilling out broken taps was not a big factor in development of left hand drills.

Left-hand(ed) drills were available - at considerable cost - well before CNC came on the scene. I can remember multi-quill drills and LH drills many years ago, but can't recall LH drills on those drills although I can quite understand that they were. "Multi" drills that I used each had it own independent quill, motor and drive mechanism - but I was in a "jobbing" and not a mass-production environment.

bruto
07-16-2008, 12:43 AM
One other, less common, application for left handed drill bits is on radial arm saws, which rotate left-handed. Left hand drill bits and endmills make it possible for a RAS with a chuck to do doweling and mortising.

doctor demo
07-16-2008, 12:50 AM
Right hand drill bits for right handed people and left hand drill bits for left handed people, just like batters and golfers!!:D :D :D
It is very easy to see the difference between l & r hand golf clubs, but I'm not sure that I have ever seen a left hand bat:D .
Steve

chipmaker2
07-20-2008, 04:52 PM
One last use not mentioned.
Left hand drills are found on the tips of left hand taps when drilling and tapping are done at one setting.

Chipslinger
07-20-2008, 05:06 PM
One last use not mentioned.
Left hand drills are found on the tips of left hand taps when drilling and tapping are done at one setting.


Wow, Really. I would have never guessed.:rolleyes:

John Stevenson
07-20-2008, 06:06 PM
You can even get left hand drills with a left hand thread on the end.

http://www.stevenson-engineers.co.uk/files/LHDrill.jpg


.

bruto
07-21-2008, 12:17 AM
It is very easy to see the difference between l & r hand golf clubs, but I'm not sure that I have ever seen a left hand bat:D .
SteveA left handed bat has the label on the opposite side, of course.:)

oldtiffie
07-21-2008, 12:30 AM
Right hand drill bits for right handed people and left hand drill bits for left handed people, just like batters and golfers!!


It is very easy to see the difference between l & r hand golf clubs, but I'm not sure that I have ever seen a left hand bat:D .
Steve

Maybe for use when you are pi$$ed and "talking left-handed"?

Or for use by a "left-footer"?

In some parts of the world a "left footer" is a "Mick" or a Catholic!!!

Don't believe it? Then check this link out:

http://www.google.com.au/search?hl=en&q=%22left+footer%22&btnG=Google+Search&meta=

rebel54
07-21-2008, 01:03 AM
Years ago they were used in screw machines.

Rustybolt
07-21-2008, 06:59 AM
Absolutly rebel. Used in a job where you'd have to tap from the turret. Because an automatic was only making money when the tool is in the work , after the tap was withdrawn the machne stayed in reverse until the tap came by again. Then the machine was thrown into forward and the tap advanced. it was just as easy to set up the forming and cuttoff for reverse. There are , or were, left hand stub reamers, box tools etc.