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Offline dray

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z axis moving up
« on: May 28, 2012, 12:09:36 PM »
When cutting 3d my z axis works it's way up out of the wood. I have tried lots of changes but nothing has helped so far. Help please!

Offline ger21

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Re: z axis moving up
« Reply #1 on: May 28, 2012, 12:21:55 PM »
Cut your Z axis acceleration in half.
Gerry

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Offline dray

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Re: z axis moving up
« Reply #2 on: May 28, 2012, 01:07:08 PM »
I have done that and did not help. I even hung a 3 lb. weight on the z axis and no help. Tried step pulse width no help. If I run an up and down loop on the z of .1 inch it will climb .04 to .05 inches in 500 cycles of the loop.

Offline RICH

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Re: z axis moving up
« Reply #3 on: May 29, 2012, 05:59:00 AM »
Make sure your steps per unit are correct.
How is the Z axis driven ...... any backlash?

RICH

Offline dray

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Re: z axis moving up
« Reply #4 on: May 29, 2012, 10:01:22 AM »
Hi Rich
yes the steps are correct for a given distance. New acme lead screw and delrin nut. It would seem to me that back lash would not cause an up word drift. There has been 2 times when it cut 3d reliefs just fine. I've checked the y axis is level with the table. The z lead screw is a 3/8x16 thread and the pulses per inch are set to 25600 pulses. Kernel is set at 25000. The steppers are 200 steps per rev and 435 in/oz The machine works fine on other types of cuts. The problem is only apparent when cutting 3d surfaces with lots of up and down movements in the z axis. I can plane a surface, vcarve and do pockets with out any issues. Also I am using 1/8 steps. Tried 1/4 steps no help. I'm beginning to think steppers do not do 3d well. But the 2 that cut nice says that may not be so. When this happens the lines of code are calling for the bit to be in the material but it is cutting air. Thanks for any and all suggestions.
dray

Offline Tweakie.CNC

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Re: z axis moving up
« Reply #5 on: May 29, 2012, 11:13:27 AM »
Hi Dray,

It sounds to me as though you may be loosing steps when the cutter enters the work, just one or two every now and again would soon mount up with 3D work.

If you have reduced your Acceleration try reducing your Velocity as well.  What are your current settings for the Z axis ??

Another possible cause of this type of problem is when the cutter is not tightly clamped in the collet and moves during the course of the work (although it is usually the other way around and ends up cutting deeper).

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline BR549

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Re: z axis moving up
« Reply #6 on: May 29, 2012, 12:02:00 PM »
I think you will find the Z lead screww is TOO FINE and you are having to run the stepper  FASTER than its torque curve will allow it to keep up and it looses steps.

Steppers run high torque at LOW rpm and require course feedscrews to keep the stepper inside its torque curve.

Try what tweakie suggested and cut the VEL setting in half as well.  IF that does not do it cut eht settings in half again.

Also you are running close to max on the kernal speed might want to consider also going up to 35K.

(;-) TP

Offline dray

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Re: z axis moving up
« Reply #7 on: May 29, 2012, 12:25:13 PM »
Thanks Guys
When it is running the loop test it is not cutting wood, just going up and down. I have tried all kinds of vel. & accel. settings. No change. I will raise the kernel freq. and see if that does it. If it has an effect I'll post the results Thanks

Offline RICH

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Re: z axis moving up
« Reply #8 on: May 29, 2012, 05:51:29 PM »
I echo what others have replied about the accel and velocity.  Post back with the results but do the testing in logical way.

I would recomend that you set your velocity to 20 IPM with an acceleration value of 2.
- ? When you jog does the Z motor run / sound smooth?
- ? How much are you gaining after the loop test?
Swap the x or y axis drive and do the same test with the same settings. Report back on those results.

POST the following:
- Pic's of your Z axis
- The xml you are using
- Pic of the driver test graph
 
Now give us the following info:
- Windows system -?
- Description of your pc...on-board graphics, PP,
- Mach version-?
- Screen set your using-?
- Type of drives-?
   - amp, voltage,micro step or any other settings
- How is the motor wired?  
- Name / description of any BOB's
- Power supply you are using / specs

Yes , I am asking for a lot, but then would like to know what your system is composed of and would rather review what you have than say a whole bunch of things that can cuase what you are experiencing.

RICH
« Last Edit: May 29, 2012, 05:54:24 PM by RICH »

Offline dray

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Re: z axis moving up
« Reply #9 on: May 30, 2012, 12:47:23 PM »
Hi Rich
hope these work this time