Entry exit arc leaving bump

[SIG]

Oi MC control.
When I use entry exit arcs while side milling a round or square boss I get a
.001 bump on side of part. The program is right but for some reason the machine never get to the final endpoint before arcing out. Does anyone have an idea why?

[rgammage]

Hi SIG

I am probably the least qualified to answer this but have you tried:

Reducing feed rate? .... I have seen m/c take a new command before fininshing the first!

Overlapping the start and finish points?

Regards

Richard

[V1T1CO]

Sig:
what I do to avoid this issue is, include an overlap, .025" should be enough, the other approach is to take a zero pass around your boss w/out retracting,...
Hope I was able to help.
Regards:
V1T1CO

[Phyrexii]

Your machine could be over (or under) compensating for backlash - put an indicator on your part, and manually move it with your handwheel a tenth (.0001), then move it back. If it is overcompensating, there will be a jump on the indicator. Under compensating would result in no movement. Fixing that is just a simple parameter change (although I don't know which one).

Also, it may be possible that you are somehow in exact stop mode? If so, the machine will pause briefly between execution of each block, and it may leave a dwell mark. I don't know how to change that offhand on a FANUC machine, I know on my FADAL I turn it off with a G08.

And, lastly, if you don't want to overlap your start and end points, as suggested, you can start and end on a corner, where a bump will not show up.

[SIG]

Hi SIG

Reducing feed rate? Overlapping the start and finish points?
Richard

Yes.
Yes that works but I was thinking shouldn't a machine with the latest control follow its intented path. I have an 85 tiger 3 that would not do this.

Sig:
what I do to avoid this issue is, include an overlap, .025" should be enough, the other approach is to take a zero pass around your boss w/out retracting,...
Hope I was able to help.
Regards:
V1T1CO

Do you have this problem too?

Your machine could be over (or under) compensating for backlash - put an indicator on your part, and manually move it with your handwheel a tenth (.0001), then move it back. If it is overcompensating, there will be a jump on the indicator. Under compensating would result in no movement. Fixing that is just a simple parameter change (although I don't know which one).

Also, it may be possible that you are somehow in exact stop mode? If so, the machine will pause briefly between execution of each block, and it may leave a dwell mark. I don't know how to change that offhand on a FANUC machine, I know on my FADAL I turn it off with a G08.

And, lastly, if you don't want to overlap your start and end points, as suggested, you can start and end on a corner, where a bump will not show up.

I'll try moving hand wheel .0001 back and forth.
I don't think its dwell because this is leaving stock on.
On a square part starting in corner does work but its still a problem on parts I'am trying to make round.
This is a new machine for me and I did check backlashes and they seem fine.
Our old machine has and 85 tiger 3 on it and would all ways follow its path. It just ran slow, so we upgraded.

When I cut a round cavity it takes .0002/.0003 off at each quadrant.
It seems like a backlash problem but I've checked them and they seem OK.
I will check them again.

Thank you everyone for your repleys

[Phyrexii]

One other thing I just thought of -

Turning cutter comp on/off - make sure you are not turning it on or off during your entry arc move. I always include an extra move there to insure that the tool is in the correct position prior to entering the cut. Cutter comp can do some strange things as the control is positioning the cutter, and may be moving the cutter off the cut early to compensate (or something ;-).

[antoon]

hi... i would suggest comping on/off to an imaginary point of the componant (away from the componant)if possible as u will allways get a slight digin where the tool has on/off in the same spot.
hope this helps
antoon

[ChattaMan]

You could also try a larger roll on/roll off arc.

[Mitsui Seiki]

I don't know what the program looks like but try to pur two "blind blocks" before G40.

[hacksaw6150]

just travel past the point where you turned comp on-then roll off

[SIG]

One other thing I just thought of -

Turning cutter comp on/off - make sure you are not turning it on or off during your entry arc move. I always include an extra move there to insure that the tool is in the correct position prior to entering the cut. Cutter comp can do some strange things as the control is positioning the cutter, and may be moving the cutter off the cut early to compensate (or something ;-).

I'am not using cutter comp just G1,2 & 3 w/ I & J's.
I also just learned about exact stop and thats not it. It leaving stock on not stock off like a dwell might do. Good idea though and I did learn something I did not know about before.
Thanks

[sinha_nsit]

I think, the bump is the result of the next command starting before the end of the previous command. This does happen. Because of this reason, if you give two pependicular moves, you will observe some rounding-off of the corner. If you want a sharp corner, use "exact stop" feature (G09) instead of just G01. Another way is to insert a dwell command between the two moves.

In your case, instead of reducing the feed (which will waste time), introduce a dwell (G04) of, say one second, between all moves where you are getting a bump. If it still does not work, try a higher dwell time. This will, of course, leave a "water mark" on the surface, but the surface will be smooth.