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Posted by Richard Edwards on April 6, 2008, 7:16 pm
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On Sun, 6 Apr 2008 21:04:28 +0100, Nigel Eaton
>writes
>>
>>> Amongst my collection I have a 7/16th Left Hand Twist drill.
>>> What would this have ever been used for. First that I have ever seen.
>>
>>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.
>
>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 <G>
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.
--
Richard
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