Turning parts on a Hardinge HC -need help

I am try to make some bolts on the HC and on my test parts (out of aluminum) I am getting way too much deflection. I expect that will carry over to the parts made from stainless steel. I'm guessing a box tool would help with turning the diameter to provide some support. Is there another way? What's happening is the diameter farthest away from the collet is greater than close to the collet. I used a geometric head to create the threads and they're ok where its fatter and flat topped where its thinner because of the deflection.
I will be using 7/16 hex 303 Stainless for the final parts. I'd guess it wont flex as much but would not produce "perfect" threads either.

Thanks

Bill

deflection = (P*L^3)/(3*E*I)

P = load,
L= length from spindle to end of rod,
E = modulus of Elasticity,
I = moment of inertia of a round cross-section.

For an estimate of what the deflection will be for the stainless, swap out the "E" for the aluminum for the "E" stainless after you back calculate the applied load "P" since you already know the deflection for the aluminum.

Typical "E" for aluminum is 10.3e6 and 29.0e6 for steel.

If I had more time I'd do it for you but I don't right now sorry.

This will just give you an estimate as there are other variables that come into play like the changing diameter but since the "E" of the steel is approx. 3 times that of aluminum, you'll see about that much difference in deflections.

Divide & conquer may help. Turn just the thread section to diameter and length. Then turn the rest of the screw. Then thread with the die head. If there is tapor and the tapor is consistant, program it out.

...can I really program it out? This is a manual machine...I will try the divide and conquer method as I wait for my box tool to arrive...this is going to be a very expensive bolt between the die head and chasers, box tool and who knows what else...eek!!!

what are the part dims?

Can you center drill and use a live/dead center in the tailstock. That would get rid of the deflection (for the most part)

HC lathe does not have a tailstock
It is an M7 bolt and 75mm long (~3 inches oal)

The box tool is the way to go. Will deffinately take care of the deflection problem.