Problems with G72 canned cycle

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Zim
Posts: 6
Joined: Fri 18 Jul , 2008 14:44 pm

Problems with G72 canned cycle

Post by Zim » Thu 10 Dec , 2009 12:32 pm

Hi,

I wonder if anyone could help me with a quick query.
I'm currently learning to use G code programming on my Novaturn but am struggling a little with the G71 and G72 canned cycle commands.

The program below carries out a G71 command to profile the outer surface of a round bar and seems to work ok.
I'm then changing tool to Tool 4 which is an end profiling tool which I am describing as boring bar with a left tip orientation.

The last seven lines of the program call the G72 command. What I'm trying to do is initially machine a straight sided pocket in the end but then to leave a pip of material standing up in the centre.

When I run this on a 2D simulation the pip is clearly visible until the last cycle of the program when it is removed. Can anyone explain why this is happening? Has it got anything to do with type I and II cycles?

I know that the pocket won't be straight sided as the shape of the tool tip will machine out extra material, but if I can get this working I make be able to modify the shape of the pocket later to offset this.

Please excuse my program if it is not very well written as I have a lot to learn!

G21
[BILLET X25.4 Z60
G28 U0 Z80
G98 G97 S3500
M06 T0101
G00 X25 Z2 M03
G71 U0.1 R-0.2
G71 P1 Q2 U0.01 W0.1 F50
N1 G00 X10
G01 Z0 F500
G03 X25 W-35 R80
N2 X25 Z-20
G28 U0 W0
M06 T0401

G00 X10 Z0.5
G72 W0.2 R0.3
G72 P3 Q6 U0.1 W0.1 F50
N3 G01 Z-5
N4 G01 X2.5
N5 G01 X0 Z-2.5
N6 G01 Z0.5

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Re: Problems with G72 canned cycle

Post by Denford Admin » Fri 11 Dec , 2009 16:50 pm

Hi,

I Can't see anything wrong with your program...have tried it in VR Turning and it looks to simulate ok (see attached).
It seems a bit odd to finish machine the clearance backwards, but I guess that is how it's supposed to work :?
Is the pip being removed when actually machining, or at the end of the simulation or both ??
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Zim
Posts: 6
Joined: Fri 18 Jul , 2008 14:44 pm

Re: Problems with G72 canned cycle

Post by Zim » Tue 15 Dec , 2009 12:34 pm

Hi, thanks very much for taking the trouble to reply. Sorry to take a while to get back to you, I think your reply was picked up by my spam filter.

I've only run the simulation so far but I get the same effect as the image you included right up until the final pass when the 'pip' disappears. I hope to get the chance to run it this week but the machine is not in the most accessible location at the minute. I am looking to rearrange my workshop to find a good home for it soon.

Could you also explain what you mean about machining the finish clearance backwards as I've got to be honest I'm not exactly sure what I should have put down. I'm not too worried about the tolerances at this moment but am interested to learn :)

Many thanks again, Clive

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Re: Problems with G72 canned cycle

Post by Denford Admin » Tue 15 Dec , 2009 13:04 pm

Because the cycle is defined, in effect, from the inside>out it does a "backwards" finish cut - it is how the Fanuc cycle is supposed to work, but just seemed odd to me as the finish would be variable depending on the shape and type of tool tip...

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