Re: Z-Axis problem - Not Enough Torque?

on large gantry machines, on the z axis a counter weight is applied
so the net weight of the post is zero, this also helps on onesided
wear on the screw. it is usually executed as an presurized air
cylender.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "WT" <pharmapack@...> wrote:
>
> Your explanations have been very helpful and it did clear up a lot
of
> questions in my mind regarding my first experience with CNC.
>
> As you have pointed out, I guess I know beforehand the consequences
when I
> used the very coarse pitch ballscrew and not even using a
belt/pulley
> reduction. As I am still experimenting on how CNC works, I did not
bother to
> get the proper or correct parts which will entail importing them
and have to
> make do with what is available locally.
>
> Time to consider doing refinements one at a time. Pulley reduction
will be
> the first and then possibly finer (5mm) pitch ballscrews later on.
I think
> the stepper motors may have enough power to drive the X and Y axis.
Z axis
> stepper motor may be a suspect.
>
> Thanks for the kind advise.
>
> Best,
> WT
>
> ----- Original Message -----
> From: caudlet
> >
> 1. Microstepping does not gain true resolution and actually
> decreases torque somewhat. Microstepping smooths out moves at lower
> speeds and reduces resonance problems. It may decrease upper speeds
> but it adds no torque.
>
> 2. Your ballscrews are way too course. You don't have enough torque
> in the design.
>
> 3. Lifting a heavy load is a lot more work that shoving it. You can
> easily shove a 200 lb weight on a level surface with moderate levels
> of friction and many times that with low coefficents of fricton.
> It's harder to left it vertically.
>
> 4. Not holding position means that the motor does not have enough
> holding torque with the given screw to maintain the down position.
> There are a lot of forces in milling depending on the type cutter,
> the feedrate, the material and the cutter type and size.
>
> Your solution is what you probably already suspect: (much) bigger
> motor, disable drive "standy" current reduction, finer pitch
> ballscrew or added belt reduction between motor and screw. It may
> take one or all depending on the ratio of change.
>