[blmmdes]

Hi all, Using Nx4.

Please have a look at attached file. My part is perfect circle and i want to finish it by z-level profile option. But when i post the program what i get is a series of quadrant movements and not a full circle movement. The problem is i am getting a small recedue at the point where the quadrant movement ends. its not acceptable. is there any way that i can get a full circle movement. For your info in post my circular motion is set to FULL CIRCLE option.
I am pretty sure that this has something to do with LOOK AHEAD of the machine as well but i need a strong arguement to explain it to our workshop supervisor who believes the machines we have are the best.

Thanks and Regards

[holbieone]

is the cut smooth or does it pause at the quadrant points ?


if the cut is smooth what you are seeing is the backlash from the axis reversal at the quadrant point

[blmmdes]

Thanks for your comments.

Yes the cut is smooth. its not stopping at quadrant point.

Pardon me, if you can explain me about backlash from axis reversal? why it happens? because of old machine and worn out lead screw?

[holbieone]

Thanks for your comments.

Yes the cut is smooth. its not stopping at quadrant point.

Pardon me, if you can explain me about backlash from axis reversal? why it happens? because of old machine and worn out lead screw?

yes a worn machine will have some backlash

what wears is the ballscrew assembly , the bearing blocks for the screw and the machine ways

on most machines you can compensate for the backlash

first you need to check the amount of backlash you have

use a 1 inch dial indicator mount it on the table parallel to an axis jog it to touch the spindle ,zero it out step in 0.01 ten times then step back ten times and compare the position of the indicator from the start

the difference will be the backlash for that axis ,do it several time to come up with an average

adjust the comp in the control and repeat for each axis


this will get rid of most the backlash

you will still see some dwell mark from the axis reversals but they should be less

also if you axis are belt driven the belts could be worn

[blmmdes]

I got an average value for backlash. How do i tell my controller about this? You said "adjust the comp in the control"
Where actually i can do this? and how

[holbieone]

what control do you have

[blmmdes]

FANUC

[holbieone]

you will have to ask someone that knows that control

sorry i can't help you with that

[blmmdes]

OK THANKS FOR THE HELP SO FAR

[COMMAND JOHN]

FANUC

How much backlash do you have most of the time it will be in the thrust bearings.

What # Fanuc control do you have.

John

[springlakecnc]

Command John is correct! most of the time the backlash IS in the thrust bearings. If you have anything over .0015 of backlash, you can't comp for it, and make your cut perfect, so say the hardcore mold cutters! put an indicator on the end of your ball screw and see if its moving, while you jog back and forth, that will tell you where the bear **** in the buckwheat....MY GOD, i'v been hanging out with old people to much!

[blmmdes]

Sorry friends,

Its not fanuc control its a Dialog11 from Grundig. I have a backlash of 0.015mm on X and Y axes. Now the question is how do i compensate for it in the controller? is there any parameter that needs to be changed? if yes, which parameter?

Thanks in Advance

[COMMAND JOHN]

Not bad but I can’t help with that control.

John

[richardfp4]

The Dialog has a direct measurement so
it cannot compensate for backlash and
it is not necessairy. This is a very precise
system usually and it will automatically
compenate for any backlash in the ballbearings
and ballbearing nut. That is because the
direct measurement is on the same location
of the spindle.

But if you have backlash in your X or Y guides
then you will have non precisie circles as
the direct measurement won't compensate
for that. You can adjust this with the tapered
keys that adjust the clearance in X and Y.

Be very carefully not to adjust it too tight as
this will cause even more problems. Just try to to tighten the tapered keys a little bit and see the effects, do it in very little steps and write down
the results. Let me know if you have any improvement. Mail me on [email protected]
I have done this myself and have seen some
improvement on our Deckel FP4NC but this was not with circels.

[blmmdes]

That was useful information Ricard. Thank you. I will try your suggesion CAREFULLY and post the results in this forum.

[richardfp4]

The easiest thing to check is to up and
down the X for example 0.05 and -0.05 and measure if your total displacement is zero after this movement. If not, this is your backlash and
you can check the tapered keys which can
cause this.
You also have to do this for Y.
If you cut a circle you should cut very
few while finishing.
What machine do you have there?

That was useful information Ricard. Thank you. I will try your suggesion CAREFULLY and post the results in
this forum.

[blmmdes]

i have a twin brother of yours. Deckel FP4A

finding out the amount of backlash is clear.

But

"If you cut a circle you should cut very few while finishing" what do you mean by that can you please explain.

[richardfp4]

Sorry for my bad english.

For example, cut only 0.1 mm and have
a feed of 0.03 mm/revolution/teeth if
you have a sharp mill. What I just mean
is to not cut for example 2 mm if this
is the last cut.

For our machine from 1984 the backlash
is only about 0.003 mm in both X and Y.
As you have a Dialog 11 which is much
newer it should be less.

i have a twin brother of yours. Deckel FP4A

finding out the amount of backlash is clear.

But

"If you cut a circle you should cut very few while finishing" what do you mean by that can you please explain.