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

Hi, Brian.

Thanks for the website but I believe the problem is not related to the
rigidity of the spindle head or column.

With my very coarse ballscrew (and hence, less friction compared to the
original leadscrew), the stepper motor I used simply did not have enough
power or torque to hold its Z position considering that I did not even use
pulley reduction.

Regards,
WT

----- Original Message -----
From: Brian Worth
To: CAD_CAM_EDM_DRO@yahoogroups.com
Sent: Wednesday, November 08, 2006 10:42 PM
Subject: Re: [CAD_CAM_EDM_DRO] Z-Axis problem - Not Enough Torque?


Hi,

Maybe you could rig up a counterweight affair similar
to what this guy did on his mill?

http://www.pathcom.com/~vhchan/cnc/cnc.html

Regards,

Brian

--- 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
>