Re: [CAD_CAM_EDM_DRO] Re: Z-Axis problem - Not Enough Torque?

At 14:26 10/11/2006, you wrote:

>If you have a slightly heavier than exact counterbalance the leadscrew
>nut will be pulled up on the leadscrew.. (you can adjust simple
>weights much more easily than pneumatic type counterbalances)
>
>When you drive the tool into the workpiece, there will be ZERO (I mean
>ZERO) backlash no matter how much backlash you have in the leadscrew
>itself.
>
>The advantage is obvious..
>
>The only time this doesn't help is if you are machining upward with a
>tool that reaches underneath the work (very unusual)

Not the only case, unfortunately. Other cases:

- Drilling (depending on the material, drills can tend to pull
themselves into the work - conventional drills in brass is one example)

- Milling in Brass - again, depending on the cutter geometry, the
cutter can be pulled into the work

- Generally, milling on the side of a workpiece with a helical cutter
(again, there will be a downforce generated by the cutting action,
the magnitude depending on cutter geometry, material, and depth of cut).

So while I agree with you that it is mostly preferable to end up with
a net "up" force on the Z axis, you have to make sure that it is
enough to resist the effects mentioned above, and not just slightly
more than needed to get exact counterbalance. Otherwise, you won't
end up with zero backlash.

Regards,
Tony