[M.RISHIKESH]

Dear Sirs

Quite often we face problems related with size variation in 2 axis Grinding and Turning machines

Like we got a 2 axes Turing machine v replaced ballscrew, end support bearings, external encoder on the shaft of ballscrew, lubrictation is ok still suddely we find vertical axis has come down by 150 microns causing scrap. When we check repeatability of axis by using dial in Automatic program for 50 cycles, we find it to be ok and repeating but only during cutting, suddenly X comes down

We also checked alignment between self centering chuck center and tailstock

Kindly advice what else is missed out

Regards,

[RCaffin]

All sorts of possibilities here, but you really have not given enough information. It is not all all clear what sort of machine you are talking about. It would seem that the problem only happens under load, not under test?

First, is the tool really secure? If that moves, all is trouble.

Second, could you be getting noise in the control electronics? The power supply to the spindle does very little work in test mode, so the currents are low and you won't get a lot of noise. Switch to cutting and the spindle draws lots more power, and the noise levels rise. Fixing that will require a skilled electronics engineer on site.

Third, is your mains supply reliable? If it is not, that could cause all sorts of problems.

Fourth, are you sure that the vertical axis has moved? Could there be creep in the metal you are machining, so that some of the dimensions change after machining?

Cheers
Roger

[M.RISHIKESH]

Thanks

a) As mentioned already, we are talking about a two axis CNC Turning lathe, yes trouble is only during cutting not during repeatably test, in fact during test we are not moving spindle at all, its an excellent suggestion, we would try testing with spindle rotating to see the difference even in test

b) Tool holders are rock solid so we do not see them deflecting on load

c) Can you please tell us on how to check electronic noise

d) Three phase Mains are fed through stabilizer and reliable

e) We dont think of any creep in the metal as similar jobs being turned in other machines of course with different slightly different Siemens CNC controllers

Eagerly awaiting your feedback

In case possible , can you please share your email id

Warm Regards,

[RCaffin]

Sounds as though you do need to do the test with the spindle running and under load, so there is some power (current) being used. My guess is that will show the problem.

Checking for noise ... ahhhh - that is one of those vague magic acts which really needs a skilled electronics engineer on site. There are so many sources or ways it could happen that remote diagnosis is almost impossible.

However, for what it is worth: I would check the screening of both signal and motor power cables, and checking that the screens are earthed at only one end. I would also check the power supply to the encoder, and maybe see whether a bypass capacitor could be of any use there. My first suspicion would be noise on the signals going to the motor driver or noise on the encoder lines coming back from the motor - assuming that your system uses that sort of control. If it is an older one using resolver feedback - not sure!
All this checking would be best done by an electronics engineer.

You can message me via this Forum.

Cheers
Roger

[M.RISHIKESH]

Sir
we are using Siemens 802d SL cnc with sinamics drive. We have checked shield with power cables for axes and spindle motor drives also for direct encoder feedback connected with sm modules. Shield and three phase supply sound good. Repeatability checked with spindle running. Variation up to 40 microns observed but almost consistent variation not random.just wrote a simple program only to move x in rapid by 20mm then in feed for 1mm dwell to check dial then to move x up by 1mm in feed then rapid.
Now tried to cut a job by keeping x up by 1mm to avoid any rejections. End
result is strange. Machine starts turning 3 different diameters
from right side and we were expecting all 3 diameter to remain oversized by
1mm but 1st dia, which is smallest, found to be 0. 8mm plus, next
bigger diameter to be 1. 2mm plus and biggest and last dia to be excess
by 2mm i.e. as x moves from one diameter to another it keeps moving up
hope I could explain. Kindly advise why x, vertical axis, keeps
moving up
warm regards

[RCaffin]

Hi

I am sorry, but I cannot debug or even diagnose that sort of problem over the web. Too complex, just not possible.
I suggest you contact Siemens and ask for a technician.

Cheers
Roger

[M.RISHIKESH]

Hi

I am sorry, but I cannot debug or even diagnose that sort of problem over the web. Too complex, just not possible.
I suggest you contact Siemens and ask for a technician.

Cheers
Roger

Thanks for your guidance