# Lefty Boring Bar



## P.K. (Nov 19, 2015)

Ooops, a brand new left hand boring bar arrived in the mail today.





Don't worry, it wasn't broken. The first thing I did was to part it off in the lathe.
And here's why.




Now I can bore some really big holes using the cross hole in the boring head.

I tried to do this with the conventional boring bars that came with the head, and since their all right-handed I had to run the mill in reverse. Big mistake. It didn't take long for the boring head to unscrew from the arbor, and voila, big crash. With this left-hand tool I don't have to worry about that.

I already have a right-hand carbide insert tool to use in the vertical holes.
I love those carbide insert tools, especially with the super sharp inserts for aluminum.


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## TommyD (Nov 19, 2015)

Could have just run it up side down too but you found a great use for a 'mistake'.


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## P.K. (Nov 19, 2015)

TommyD said:


> Could have just run it up side down too but you found a great use for a 'mistake'.



It didn't brake off. I parted it off in the lathe for this purpose.


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## TommyD (Nov 19, 2015)

I made no mention of anything 'braking'. Sorry if you misunderstood.


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## P.K. (Nov 19, 2015)

TommyD said:


> I made no mention of anything 'braking'. Sorry if you misunderstood.



OK, no problem 
I have to admit I didn't think of running them up side down.


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## Chuck K (Nov 19, 2015)

P.K. said:


> Ooops, a brand new left hand boring bar arrived in the mail today.
> 
> 
> 
> ...


I like your style.  Take a new tool and cut it in half so it fits your needs.


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## joshua43214 (Nov 19, 2015)

I am so glad you posted this. I have a project coming up soon that I planned to run my boring head in reverse to make a wide radius.
Somehow I just never considered the arbor screws on...


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## Chippy (Nov 20, 2015)

TommyD said:


> Could have just run it up side down too but you found a great use for a 'mistake'.



Could you elaborate a little more, I too just picked up a left handed boring bar for the same reason and I'm not sure what you mean by running it upside down.


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## TommyD (Nov 21, 2015)

So, you can bore the opposite side of the bore, the side furthest from you, but the spindle rotation needs to be reversed so the mat'l is coming down onto the cutting edge, correct? Put your boring bar in your workholder upside down, this will put the cutting edge on the closest to you side of the bore. Put the cutting edge on center, reverse spindle rotation and go to town. Opposite spindle rotation direction puts the material coming UP and onto the bits cutting edge. You can turn as well as face doing this.

We would have to do stuff like this when the bearing caps on our Southbends would wear and cause the spindle to hop around, chatter and bad finish. By placing the bit upside down on center all the cutting forces would be forced DOWN onto the lower bearing from the spindle rotation direction. We''d finish up our work then start diddling with the top bearing cap.


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## Chippy (Nov 21, 2015)

TommyD said:


> So, you can bore the opposite side of the bore, the side furthest from you, but the spindle rotation needs to be reversed so the mat'l is coming down onto the cutting edge, correct? Put your boring bar in your workholder upside down, this will put the cutting edge on the closest to you side of the bore. Put the cutting edge on center, reverse spindle rotation and go to town. Opposite spindle rotation direction puts the material coming UP and onto the bits cutting edge. You can turn as well as face doing this.
> 
> We would have to do stuff like this when the bearing caps on our Southbends would wear and cause the spindle to hop around, chatter and bad finish. By placing the bit upside down on center all the cutting forces would be forced DOWN onto the lower bearing from the spindle rotation direction. We''d finish up our work then start diddling with the top bearing cap.




Thanks for the detailed explanation. I assume you are talking about using the boring bar in the lathe, but the OP and myself are trying to avoid running a boring head in reverse so it dosnt unscrew itself  from a threaded spindle. After thinking more about it, tuning the boring bar tool upside down and starting from the bottom of the bore, working up to the top, would work, as long as the bore goes all the way through. Thanks again.


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