[machrychar]

Hi everybody,

New on the forum as well as on machining stuff, I'm having trouble with G71 cycle on Fanuc 21T.
I want to profile an arc (120 degrees, radius 25 mm) with a R style insert. I'm using G42 to correct the tool nose radius (4 mm) but when it passes the 90 degrees point, that's the back of the tool that cuts the profile.
Shall I change G42 into G41 at that point and so it might correct the back of the tool?
I'm a bit lost!

Hope all this is understandable enough in English.

Regards

JL

[Hulkster]

Hi! I have just been thru such a thing as yourself. Apparently Fanuc does not like G42 to be active in the G71 cycle. It should only be used in the G70 finish cycle. For the type of radius that you are doing, you need to set up your tool as a type 8, and set it up as so. The whole profile will be G42, because you will always be to the right of the programmed tool path. G42 with a type 8 setup will calculate compensation even when it is cutting on the back. The roughing out will have to be manually programmed, it would only work with the G70 finish cut cycle. Hope this is helps.

[machrychar]

Hi Hulkster

Thanks for your reply.
In fact, as I couldn't get the parts good enough, I programed them on another lathe with NUM command.
As for Fanuc, I've also noticed that G71 cycle doesn't like G42 and I use it only for the finish cycle G70. I didn't think to set up the tool on T8, I should try this the next time I have those parts to do.

Thanks again and sorry for having been long to get back to you.

Regards

JL