Backlash compensation value effectiveness

[Jaani]

A Doosan Puma 300M lathe machine with Fanuc 32i has 0.07 mm backlash in Z axis. By setting the value (70) in parameter 1851, nothing changes. Tried different values but the same. What could be the reasons?

 

[mach ramsey mn]

How are you measuring it? This is a significant amount of backlash. That much would surly be different along your screw unless it was a bad thrust bearing or some other lost motion issue.

 

[Jaani]

@mach ramsey mn
By attaching a dial indicator base to chuck (In lock mode) and making the turret close to it in Z direction. 0.1 mm load in 0.01 steps then reverting in Z.

Yes it is significant, but inputting the value with no change in result is normal?

 

[mach ramsey mn]

Even in a manual mode I would think you would see the indicator “flicker” at axis reversal. Are you at least giving your indicator like .5mm load against your turret before reversal? I have made a little program and looped it to see if I can watch the backlash in motion.

 

[lobust]

Are you checking it with the handwheel or in MDI/auto?

 

[Jaani]

I check it in handwheel mode with an indicator preload of .4 mm. Should I check backlash in Auto and motion?

 

[Herding Cats]

IIRC there are different backlash parameters for auto and manual modes. But my memory could be referencing a Mitsu or Yasnac.

That is a massive amount of backlash and you will likely still have issues even with it accounted for in the control.

If you account for it in the control, when doing tasks such as facing you need to make sure every pass is approached in the Z- direction, otherwise the tool will likely push off the face as you are cutting if approached in the Z+ direction. Grooving and cut-off could give issues also.

IMO you need to address the mechanical issues first so your backlash comp can be in the single digits where it belongs.

 

[mach ramsey mn]

But is the 70 value in .000, .0000 mm or in pulse count or?

 

[Herding Cats]

These parameters are from a 16i manual so verify for your control.

1800.4 may need to be enabled for backlash comp, the manual isn't very clear

1817.2 smooth sets smooth backlash comp which is set with parameters 1846 1847 1848

I would assume if 1817.2 is a 1 then you use 1846-1848 and is 1817.2 is a 0 then you use 1851

 

[Herding Cats]

But is the 70 value in mm or in pulse count or?

Regardless he said it has 0.070mm of mechanical backlash which in my opinion is a mechanical issue

 

[Herding Cats]

Also the manual notes that the power must be cycled for these parameters to take effect.

 

[mach ramsey mn]

Regardless he said it has 0.070mm of mechanical backlash which in my opinion is a mechanical issue

 

[mach ramsey mn]

Agreed this is enough to almost make noise. Clunk if you will.

 

[mach ramsey mn]

Also the manual notes that the power must be cycled for these parameters to take effect.

I recall this now and if I remember correctly you have to wait for the drives to “leak” down. The LED’s to go out on the drives.

 

[Barbter]

If you have that now, it will only get worse fast - probossibly!
I would do a quick appraisal and see what it is like at different points along the Z.
If it is all the same, check the nut is tight (!) and then look at thrust bearing.

 

[mach ramsey mn]

Thrust bearing, motor mounts, misalignment coupling, Gibbs and straps. If linear ways look for a loose truck…

 

[Mud]

Also the manual notes that the power must be cycled for these parameters to take effect.

Well that would suck. I never would have guessed that.

 

[angelw]

Well that would suck. I never would have guessed that.

All the parameters that require the power to the control to be cycled, raise an alarm as soon as any are modified; you won't miss it.

Regards,

Bill