Left Hand Drill?

I've seen old industrial drills that rotate left hand, cant remember why or what was being drill though! Unless it was for a left hand thread ;~) Bob

Could they be for CNC type work were the work has been rotating clockwise for some other operation on a back tool post, one less motor stop/start IYSWIM?

The main use in ye olde times was for multiple spindle gear driven drilling heads where alternate heads run in opposite directions rather than employ two gears per drive to keep the rotation in the same direction at extra cost and complexity. There's no actual drilling benefit in the direction of rotation unless the machine itself requires it other than supposedly sometimes for drilling out broken studs where you want any forces acting to try and remove the stud not drive it further in. Personally I've never come across a stud so corroded into place that it needed drilling out that could have been affected in any way by the direction you then drilled into it. They generally won't even budge once you've drilled them and then screwed a stud extractor in.

In article , Dave Baker writes

I use them fairly frequently for getting knackered studs / sheared bolts / stuff out of Japanese motorcycles. They really do a nice job, in my experience. I start off with a small size, then work up. Usually the bit grabs the bolt / stud / whatever before I get anywhere near the threads and spins the remnants out.

Thanks to everyone for the replies. The drill is a "Double Mushet" of reasonable vintage so I feel the CNC option is not a goer in this case. next time I have a broken stud with a core diameter greater than

7/16th I have the tool Until then I will pass it to friends and ask them if they can grind it for me as I cannot get it to cut! It will go in the box with the 15mm x 1mm and 17mm x 1mm taps that I have yet to find a use for.

It's for driiling holes in the southern hemisphere and confusing folks who try to sharpen it.

John

Absolute nonsense! It's for drilling left hand holes into which you park your left hand screw driver. Bigger ones are for left hand hammers. Put a peg into the hole and you can hang up packets of wire netting seed.

Henry PS Where's Tony Jeffree when you need him? He's bound to have a better explanation!

Beat me to the punch there Henry...

Regards, Tony

Why does the southern hemisphere need holes?

To keep the planet balanced.

Chris

Hi all I think that the government will soon be making left hand drills compulsory in order to put a new twist on the hole they have gotten us into Regards Alan

From next April 1st any workshop employing more than 5 staff will have to have a minimum of 6% left hand drills in the rack and no more than

10% to ensure a national balance in the workplace. You have been warned! Bob

Don't you need a left hand drill if you're gonna tap a reverse thread into something?

Chris

Perhaps so, but isn't a right hand thread reverse downunder?

OK, look, I'm probably going to get in trouble for telling you this...

You know those times when you pick up the wrong drill bit? You go for the 5/32 and you grab an 11/64 by mistake and your arms aren't long enough to read the faded markings on the bit?

Yes. Those times.

Well, then you need the LH bits.

Pop an 11.64 *LH* bit in the drill, reverse the motor and have at it.

You may have to make a couple of passes (particularly in harder materials), but eventually you'll put it all back. If you're careful you can even get a pretty good finish (although that's hard in some grades of stainless, be careful that it doesn't unwork-harden. You want to be laying down at least .002" per pass).

There.

Now the secret's out.

Used in multi spindle drilling machines, some of which have counter rotating spindles.

Handy for drilling out broken off bolts or studs, as they sometimes catch, and wind the stub out of the hole. Not much good in a keyless chuck, though.

If you should happen across a catalog for a proper tool dealer, like as not, they will have some.

Cheers Trevor Jones

Similar principle to the microwave freezer then

Regards, Tony

So it's a putting on tool then.

John

Thats right...it un-drills holes.

Regards, Tony