Z Axis problem Need help Badly Please anybody

[rodzilla]

I am having a problem with my Z axiz stalling on my Harbor Freight Round Column Mill. I just converted it to ball screw from using the fine feed worm gear that is built into the Z axis. I didn't have any problems with the old setup as far as the axiz diving into metal without stalling but since the conversion i can't seem to get it to feed into the metal without stalling

My motor is a Sanyo Denki 720oz in motor 12-300VDC 6.0A with a 20 tooth gear on the motor and a 33 tooth gear on the ballscrew i have the steps per set at 16500 which is giving me the correct accuracy i just lost all sorts of torque what can i do to get this back. The current on the Gecko G202 is set at 270K ohms it calles for a 285K ohms resistor but i can't find on the closest i could come was 270K ohms. I have these same motors on my X and Y axis with no problems i would think the motor specs would have enough torque to drive the axis direct without using gear reduction

[Torsten]

Just courious why did you change it from driving the finefeed worm.
Most of the Backlash with this setup could be eliminated with some good engineering.
It would probably never be quiet as much as with a Ballscrew but if you
can get it down to a few tousands, overall this may be better?

What I would suspect with your current Ballscrew convertion is that it is binding up under load because of the offcenter force pushing the Quill?

[rodzilla]

<Quote>What I would suspect with your current Ballscrew convertion is that it is binding up under load because of the offcenter force pushing the Quill?</Quote>

I wouldn't think that would be the problem as i've seen others using the same aproach with success Jeff Davis (HomeCNC) is one of them i have also seen others on this site using the same approach.

[rodzilla]

Wow this is hard to believe that nobody can help me out with this problem

[Oldmanandhistoy]

Hi,

Not sure I can help but as you aren’t getting any from anyone else at the moment I will try.

What rpm are you turning the stepper motor?

Is it wired bipolar parallel or bipolar series?

Do you have the torque curves?

Am I right to presume you have the stepper motor Amps set correctly, you checked gib adjustment and the axis runs smooth (mechanically)?

I can’t help you with the Gecko drive as I don’t use them.

John

[rodzilla]

I'm not sure what RPM they are running at how would i check this out.
as far as wiring it is a 4 wire motor i am assuming series wired
No i don't have the Torque curves for these steppers
I have the stepper motors current set correctly. Everything is wired the same as it was when i had good torque the only difference is i am using a ball screw to feed the axis instead of the fine feed i just can't figure out if i should be running direct connected or gear reduced for maximum torque as i have tried both with limited results

[Oldmanandhistoy]

By gearing down you would gain more torque but this means you need to turn your stepper motor faster and as the stepper motor speed increases you loose torque from the stepper motor. This is usually ok on a Z axis as feeds are usually lower.

What TPI is your ballscrew?

Four wire motors are wired internally either series or parallel as far as I know.

[rodzilla]

ball screw has a .2 screw lead

[Torsten]

Running a .2 lead Ballscrew at a 2:1 ratio would
be the same Transmission ratio as you had when
driving the Fine feed at 1:1 ratio.
There is a .1 Quill advance per rotation of the fine feed wheel.
Because the Ballscrew would have a much higher efficency
it should leave you with more Power to spare.

Maybe the problem is in your mechanical implementation?

[Robin Hewitt]

What is this 270k Ohm resistor? To drive 6 Amps through 270k would take 1,620,000 Volts and you would have to dissapate 9,720,000 Watts of heat. Obviously I am misunderstanding

I have much the same set up with a 2:1 belt reduction. I chose 180 oz-in Escap Disk Magnet motors because they hold their torque at speed. How fast are you trying to run it? Perhaps the motors are washing out?

Also don't uderstand 16500 steps per, is this steps/rev? I use 400 which seems suited to the accuracy of the machine. Perhaps you can't rattle the computer interface cable fast enough to keep up?

[MarkWink]

...my HF X2 (ballscrew driven) head binds after extended runs at high speeds

-the heat that builds up causes the head to grab the column.

The build quality is pretty poor on my X2

[Rat7734]

I have a simular mill and when I recieved it the return spring for the quil was set way too tight and the mill would feed down very slowly and sail back up. When I loosened the spring tension that cured my problem. perhaps that may also help you.Now I will ask the dumb question no one else has asked. Is the spindle lock off?