# Thread: Need help with G68 roughing cycle.

1. ## Need help with G68 roughing cycle.

Seldom use the G68 cycle because it is such a pain to get it running right. I had one that bored one diameter that worked. Program had been sent back from lathe so I know nothing is wrong with it. I modified it to run a slightly more complicated bore. Only way I can get it to run is by making P7 = K0. If I leave stock for finishing (such as P7 = K.005), it alarms out with the 004 alarm. Makes no sense to me.

N10 G0 (G68 CYCLE)
N20 G97 S2000 M3
N30 X -.95 Z1. T08.08
N40 G92 S2000
N50 G96 S500
N60 Z.02 F.003
N70 G68 P0 = K -2.75 P1 = K0 P5 = K.02 P7 = K0 P8 = K.001 P9 = K.003 P10 = K1 P13 = K110 P14 = K170
N80 G0 G97 Z.5 M5
N90 X0 Z0 T0.0
N100 M30
N110 X -2.75 Z -.21
N120 X -2.17 Z -.21
N130 X -2.164 Z -.212
N140 X -2.162 Z -.212
N150 G3 X -1.88 Z -.353 I0 K -.141
N160 G1 X -1.88 Z -.66
N170 X -.95 Z -.66

Don't worry about the shallow DOC and slow feedrate. I think this lathe is the one with a 1/2 HP motor. .03 DOC at F.004 stopped the spindle around 2.3 diameter.

Thanks.

2. I've been asked to "Post the definition and parameters of the Fagor G68 cycle for lathe and the meaning of the 004 alarm to your thread"

P0 = Absolute X coordinate value of the starting point
P1 = Absolute Z coordinate value of the starting point
P5 = Max. DOC per pass (radius). It must be greater than zero.
P7 = Finishing stock allowance along X axis (radius). Must be equal to or greater than zero
P8 = Finishing stock allowance along Z axis (radius). Must be equal to or greater than zero
P9 = Feedrate of the finishing pass. If P9=0, there will be no finishing pass: but there will be a final roughing pass maintaining the excess material indicated by P7 and P8. If it has a negative value, neither a final roughing pass nor a finishing pass will be carried out.
P10: This parameter must be assigned a value other than "0" in order for the CNC to carry out a final roughing pass prior to the finishing pass.
P13 = Number of the first block to define the pattern
P14 = Number of the last block to define the pattern. It must be greater than P13.

A couple notes (there are others) that follow the definition/parameters in the manual are:

The machining conditions (feedrate, spindle rotation, etc.) must be programmed before calling the cycle.

If arcs are included in the definition, they must be programmed with the center's I,K coordinates, referred to the arc's starting point and with the relevant sign.

You may have noticed I include I0 in the program. This is necessary or it will give you an error message for the arc. It is also necessary to include an X and Z value in each block even if they are the same as in previous block(s).

004 alarm states: A canned cycle has been defined while function G02, G03 or G33 was active.

This alarm is very confusing as you don't need any of those commands anywhere in the operation to get it. As you can see, there are none in my program until near the middle of the contour.

I just went out and deleted the G3I0K-.141 and made P7=K.005. Received 004 alarm. Changed back to "0", and it ran. With the G3 removed, there is nothing in the program except G0 and G1 so where is the 004 alarm coming from?

3. The G68 cycle is commonly used and works well. If you are still having issues, call our 800-423-2467 number and talk with Service Department.... send them the information from your 1st post and they can quickly and easily help you. They will probably simulate the problem and report back to you what they experienced.

hope this helps.