Re: Z-Axis problem - Not Enough Torque?

Hi WT,

If possible I suggest that you change the ballscrew of Z-axis, as
others have said, the pitch is too course. It seems that the ball
screw is for some sort of fast movement applications, not for mills.
Even if you add a reduction gear, the force on the threads is still
the same, way too big IMHO. It's better to find a ball screw which
has 5 mm lead.

Regards,

horace.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "WT" <pharmapack@...> wrote:
>
>
>
> Hi, all.
>
> I think I have a problem with my Z-axis not having enough torque
and will
> appreciate some suggestions and recommendations on what are the
possible
> solutions.
>
> Following are the specs of my CNC retrofitted milling machine:
>
> 1) ZAY7032 Mill/Drill Machine, 2 HP spindle motor
>
> 2) X & Y-axis:
> converted to ballscrews: 20 mm diameter x 20 mm lead pitch (4
start x 5 mm
> lead pitch),
> direct coupled to a stepper motor (Nema34, 4.2 N.m, 6.0A, 2.4Vdc),
> stepper driver capable up to 7.8A, 80VDC, microstepping (2, 4, 8,
16, 32,
> 64, 128, 5, 10, 25, 50, 125) and presently set at 5.7A, 25
microstepping, &
> 37VDC
> Mach3 - 250 steps/mm, 2000 mm/min
>
> 3) Z-axis:
> converted to ballscrew: 15 mm diameter x 40 mm lead pitch (3 start
x 13.3333
> lead pitch),
> belt driven (same ratio/no reduction) by a stepper motor (Nema34,
4.2 N.m,
> 6.0A, 2.4Vdc),
> stepper driver (same as above) but set at 50 microstepping
> Mach3 - 250 steps/mm, 1000 mm/min
>
> 4) Power supply:
> Has multi-tap output capable of 37, 47, 52, 59, 65 VDC,
> currently using 37 Vdc,
> about 1 KVA
>
> Presently, the X & Y-axis seem to be working very well with no
backlash and
> lost step. However, the Z-axis seems incapable of moving up
correctly under
> load or when cutting or milling. Also, noticeable chatter or
vibration of
> the spindle head when milling MS plate at only 0.2 mm downfeed and
100
> mm/min feedrate.
>
> 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
>