Need Help!- Ball bar test

[Scottjit]

I have a 40x60 YCM mill that is cutting .009 out of round. I ran a ball bar on it and tried to adjust it in. I changed 1851, 2048, 2025, 2071 and a few others and can not get the Circularity and better than .008". I have moved each parameter one way and then the other and each way seems to make it worse. Any help on which parameters to adjust for my problem would be great.

Scott

[John_B]

Have you looked at the mechanicals yet? That much OOR sounds like there is too much play in the screw or bearings.

[Scottjit]

Sorry the I left out a "0". The machine is out .0008 in a circle and the ballbar Circularity .0008". Yes we checked the bearings and ball screw .0003 / .0002. Can comp out with a number in 1851 X=800 Y=400. Adjusting these up or down with the ball bar did not help.

[Stevie Bramwell]

Hi,

What are the individual errors in your test? as opposed to the overall circularity i.e. Backlash, Reversal Spikes, Squareness etc.

Are you able to take a screen dump and post the results on here including the graph?

The other option would be to send the results file to me and I'll look at it on my Ball Bar PC, however I'm not back at work until Saturday.

I hope I can be of help.

Stevie

[Scottjit]

This is a scree shot of the Ball Bar.

Scott

[Stevie Bramwell]

Hi Scott,

I've had a quick look at your screen shot.

If my memory serves me right then I think that your X axis is lagging the Y axis.

This means that the servo drive isn't reacting as quickly.

This can happen if the slides are tight i.e. a lube issue so it may be worth checking this out.

You can adjust a parameter to quicken the response time of the servo so that it keeps up.

I can't remember off the top of my head but I think it is the servo loop gain parameter. I think they are normally set to a figure of 3000.

I've sent you a PM giving you my email address. If you send me the file I will look into it further when I'm at work on Saturday and give you more detail.

I hope this helps

Stevie

[Stevie Bramwell]

Hi Scott,

I was called into work today.

Parameter 1825 - Servo Loop Gain should improve the servo mismatch.

Adjust the X axis parameter. Try adding 100 to the figure and retest. I think this should be close to what error is showing. You may have to see how much it improves it by and then re-adjust.

Parameter 1851 will compensate the backlash (You've already mentioned this).

This should take out the worst errors on your machine and you should then see a good improvement in the circularity.

I hope this helps.

Let me know how you get on.

Stevie

[NICK1945]

.009 shows that you have mechanical looseness check the lock nut on both axis it must be loose you can put a small ball bearing at the end of the lead screw and put a .0001" dial indicator on it and move the axis back and forth and if you have over .0005" your lock nut or bearings are at fault.
Let me know good luck you dont need a ball bar test for that amount of looseness or your gibs are too tight.