Re: Z-Axis problem - Not Enough Torque?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "WT" <pharmapack@...> wrote:

>
>
>
> Hi, all.
>
>>
> I know my ballscrews are very coarse pitch but I have to live with

it as

> that is what is presently available to me. And hence, the reason I

set up

> the microsteppings to 25 (X & Y-axis) and 50 (Z-axis) to gain more
> resolution. Considering that the X and Y-axis are capable of

moving the

> heavy X/Y table, is there any reason why Z-axis can not hold its

position

> under load?
>
> So, are there any solutions or suggestions to solve the problem

within the

> present hardware parameters? If not, what hardware changes should

I make?

>
> TIA for all your kind response.
>
> Best,
> WT
>

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.