Mounting parting tool upside down

[taiwanluthiers]

I found when I mount a parting tool this way, and turning the lathe backwards, I'm able to part a large diameter 4140 steel with the parting tool sticking out almost 2 inches without breaking any inserts. I've also noticed CNC lathes run this way, it turns clockwise when turning, and only counterclockwise when drilling or boring. I'm thinking of mounting ALL my turning tools this way because there are other benefits, such as the chips naturally falling into the chip pan instead of flying all over the shop when turning.

This somehow increases the rigidity a lot, even if your actual rigidity isn't that good.

Anyone care to explain why?

 

[davidpbest]

This could be because your compound deflects more when pushed down (conventional tool mounting position) than when pulled upward (tool upside down, spindle reversed). On many lathes, the compound-to-cross slide mounting is the least rigid interface, plus the tendency is to have the cutting tool wound out in a cantilevered position. Throw an indicator on the tool shank near the cutting action and do some rigidly tests. I ended up transitioning to a solid tool post, taking the compound out of the equation completely, and a it made an enormous difference - particularly on parting operations.