Puma 240M live tooling machining oval holes

[Bhogg]

I need help with correcting a C-axis problem on a Puma 240M lathe where the live tooling is machining oval holes (should be round).

[Bhogg]

We have two of the Puma 240-M's in our shop. One has a gantry loader and the other does not. We are making a part with a small threaded hole in the centre and 6 straight thru holes around it on a 4" pitch circle. The perimeter holes are 3/4" and are cut using a 1/4" end mill. The part comes out with oval perimeter holes. It almost appears like a backlash problem but both machines are doing the same thing and I'm not sure where to begin correcting the problem.
The funny thing is the machine can drill holes accurately on a similar pitch circle, but cannot seem to machine a hole out with out producing an oval.

Has anyone seen this before? Any help would be much appreciated.

Cheers,
Brendan

[dcoupar]

I've seen this when the live tool had an X Geometry or Wear Offset value. You should check that the centerline of the live tool is on the spindle centerline at X0.

Also, are you using the spindle clamp (M88) when interpolating the holes? Possibly the clamping pressure is set incorrectly not allowing the c-axis to rotate correctly.

[MysticMonkey]

I have seen this where the C-Axis is not setup correctly, or a parameter has been altered.
If this 'was' working correctly then it will probably be a operator error.
double check all your parameters against the blue book and post any differences here.


If this has been like this since you got the machine.

Get Fanuc in to tune the servos. It is quite easy to do with Servo Guide.

[Bhogg]

Thanks for the replies!
Both machines have been doing this since we purchased them. One is a little worse than the other. We had a couple of techs in to work on it last year but the problem was not so evident on the parts we were doing at the time.
I'm afraid getting someone in here again is not going to go over well with management as we would have to pay for air-fare, accommodation etc again.. I'd like to do what I can to narrow down the problem myself before calling in a tech. FYI I live in Victoria BC Canada (on an island) near Vancouver.
I don't think its a wear offset issue because the holes are out of round by about .060 or more. We are not using an M88 although that was a very good idea - I ran out to talk to the operator about it as I was reading your reply. The live tool spindle is definitely on the machine centreline X0 (both machines).
Is there any way I can tune the servos myself? perhaps I can get it closer?
Finally can you please elaborate on this?
"double check all your parameters against the blue book and post any differences here."
Not sure how to go about this or if its relevant given this post.

Thanks very much.
B

[Jaguar]

Are you using the low pressure clamp during the machining op?

The blue book is in the back of the machine and it contains a list of parameters and keep relay settings, timers, etc.. You should make every effort to understand this book if you are going to get the most out of your Doosan lathe. it can be a lifesaver from time to time.

J

[Bhogg]

Ok, thanks Jaguar. I have the blue book (mines actually yellow) and it covers FANUC series 21i-MODEL B and 210i-MODEL B.
There are over 50 parameters covered in the manual - are there some specific ones which I should check first? I think parameters which cover interpolation between the C-axis and or the chuck rotation would be the first ones to check. Does it take a long time to check all the parameters? Forgive my ignorance - I have never checked parameters before and its not something we typically do in our shop.

Thanks,
Brendan

[Jaguar]

The yellow books are the Fanuc books, you want the BLUE book out of the back of the machine electrical cabinet. Did you turn on the low pressure clamp when you machined the holes?

J

[Bhogg]

No the low pressure clamp is not used during the operation. Next week I'll take a picture of the part and post it up to give you a better idea of what's happening.

B