Replace the lead screw in the knee of my bridgeport?

[dabear3428]

I know that ball screws are much better than lead screws from a friction and backlash stand point but, I have an eztrak mill with ball screws on x&y and a lead screw on the knee. because the weight and cutting forces and most often in the same direction backlash should be non-existent, and as to friction leaving the lead screw in will keep me from having to use a break on the servo to keep the knee in place when the servo is off (i want to be able to use the mill in manual with the CNC off).
with the exception to up force from mill helix I'm not expecting backlash, opinions?
i plan on driving the lead screw directly bypassing the bevel gear and going with a large servo with gear reduction to overcome the friction. does anyone see a problem with this plan?

 

[markba633csi]

No problem with the plan as long as your motor has enough torque- I would measure it with a torque wrench
plus add a percentage for good measure, for example if you measure 24 foot pounds I would round it up to 30
Does the bevel gear add or subtract from the ratio? Have to consider that too

 

[dabear3428]

No problem with the plan as long as your motor has enough torque- I would measure it with a torque wrench
plus add a percentage for good measure, for example if you measure 24 foot pounds I would round it up to 30
Does the bevel gear add or subtract from the ratio? Have to consider that too

the bevel gear adds tq multiplication, I think i have a handle on load and may add a gas spring to offset some of the static load.